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SCIENCE FOR SOUTH AFRICA

ISSN 1729-830X

VOLUME 1 • NUMBER 4 • 2005 R20 incl. VAT

ACADEMY OF SCIENCE OF SOUTH AFRICA


Cover stories

24

Wonderful spiders

Ansie Dippenaar-Schoeman Spiders for silk threads and smart hunting 3

Genomics ■ Genomics fights TB Eileen Hoal and Paul van Helden Stopping the spread of TB

7

11

Contents

■ Understanding the TB bacterium Bavesh Kana and Valerie Mizrahi How TB works its devastation

■ Why it’s so hard to combat AIDS Darren Martin Fighting the ever-mutating virus

VOLUME 1 • NUMBER 4 • 2005

Regulars 13

14

Science news

Elephantine dilemmas

Water (and life?) on Mars (p. 22) • Red’s a winner; A drink a day (but no more) (p. 32) • Bringing science to the people: object lesson for SA? (p. 34) • The Sombrero galaxy through different eyes (p. 39) • SA support for world’s first Ka-band TT&C satellite (p. 45)

David Cumming The elephant population debate

33 20

Features 23

Eat right & live longer

35

Careers Engineers in a big industry

37

Your QUESTions answered DNA and taxonomy

37

Measuring up

38

QUEST interview Painting Einstein – Harold Voigt

40

Books Cotyledon and Tylecodon, by Ernst van Jaarsveld and Daryl Koutnik • and other titles

42

The S&T tourist Nature amid the glitz

Alex Walker Why not change to a healthy lifestyle?

30

The Namib’s amazing fossil spider webs

Martin Pickford Spider secrets in the sand

Viewpoint Backing the GMO horse: what are the odds? Melodie McGeoch

Bringing queues into line

Sarma Yadavalli, Kris Adendorff, Gert Erasmus, and Yegna Narayanan Mathematics to control queues

Fact file TB and HIV: deadly alliance

Visit the Pilanesberg’s animals and Sun City’s botanical gardens 45

Crossword puzzle

46

Letters to QUEST

47

ASSAf news

47

Diary of events

48

Subscription form • Back page science

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Survival of living things A Green flower crab spider (Thomisidae, Synema). Photograph: Norman Larsen (Reproduced courtesy of the ARC-Plant Protection Research Institute)

SCIENCE FOR SOUTH AFRICA

ISSN 1729-830X

Editor Elisabeth Lickindorf Editorial Board Wieland Gevers (University of Cape Town) (Chair) Graham Baker (South African Journal of Science) Anusuya Chinsamy-Turan (University of Cape Town) George Ellis (University of Cape Town) Jonathan Jansen (University of Pretoria) Colin Johnson (Rhodes University) Correspondence and The Editor enquiries PO Box 1011, Melville 2109 South Africa Tel./fax: (011) 673 3683 e-mail: editor.quest@iafrica.com (For more information visit www.assaf.co.za) Business Manager Neville Pritchard Advertising and Neville Pritchard Subscription enquiries PO Box 130614 Bryanston 2074 South Africa Tel.: (011) 781 8388 Fax: (011) 673 3683 Cell: 083 408 3286 e-mail: pritchardn@mweb.co.za Copyright © 2005 Academy of Science of South Africa Published by the Academy of Science of South Africa (ASSAf) PO Box 72135, Lynnwood Ridge 0040, South Africa (011) 673 3683 Permissions Fax: e-mail: editor.quest@iafrica.com (011) 781 8388 Back issues Tel.: Fax: (011) 673 3683 e-mail: pritchardn@mweb.co.za Subscription rates (4 issues and postage) (For subscription form, other countries, see p.48.)

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Production Pritchard Productions cc Design and layout Creating Ripples Printing Paradigm All material is strictly copyright and all rights are reserved. Reproduction without permission is forbidden. Every care is taken in compiling the contents of this publication, but we assume no responsibility in effects arising therefrom. The views expressed in this magazine are not necessarily those of the publisher.

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t the heart of much scientific curiosity is the remarkable variety of living things. Researchers examine the effects of organisms on one another and tell story after story of life-and-death struggles for survival. They keep verifying Charles Darwin’s memorable observation (On the Origin of Species, ch. 3) that “In looking at Nature, it is most necessary ... never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals.” This issue of QUEST shows some of the ways in which living things large and small interact in a “web of complex relations” as each tries to escape destruction. In the front line of the struggle against the devastating coepidemic of TB and HIV/AIDS, for instance, researchers work with dangerous bacteria and viruses, too small to be seen by the naked eye, to clarify the extent of the threat to humans (p. 3), TB’s strategies to kill its victims (p. 7), and how the deadly virus HIV survives by dodging and destroying the human immune system (p. 11). Only by understanding the minutiae can scientists hope to find ways to beat the pandemic. In other contexts there’s hot debate. Genetically modified organisms might solve the problem of providing enough food to end starvation, but are they safe enough to grow freely (p. 33)? Another dilemma has to do with the way humans coexist with others. As elephant numbers grow, so also does the debate about containing the damage they can cause. To cull or not to cull is the question (p. 14). These are issues for the general public as well as for people who make policy, but scientists have to provide the facts on which responsible answers hang. Sometimes the facts are surprising. Animals that are traditionally feared and maligned – such as spiders – can turn out to be allies, fighting the pests that destroy our crops, for instance (p. 24), and they reveal secrets about ancient climate changes when their webs reappear in the fossil record (p. 30). It’s up to scientists to find and tell the facts of life – what kind of diet offers long-term health (p. 23)? what to do about queues (p. 20)? Then it’s up to us to decide how to act on the evidence.

Elisabeth Lickindorf Editor – QUEST: Science for South Africa Join QUEST’s knowledge sharing activities ■

Write letters for our regular Letters column – e-mail or fax your letter to The Editor and win a prize. (Write QUEST LETTER in the subject line.) ■ Ask science and technology (S&T) questions for specialist members of the Academy of Science to answer in our regular S&T Questions and Answers column – e-mail or fax your questions to The Editor and win a prize. (Write S&T QUESTION in the subject line.) ■ Inform readers in our regular Diary of Events column about S&T events that you may be organizing. (Write QUEST DIARY clearly on your e-mail or fax and provide full and accurate details.) ■ Contribute if you are a specialist with research to report. Ask the Editor for a copy of QUEST’s Call for Contributions (or find it at www.assaf.co.za), and make arrangements to tell us your story. To contact the Editor, send an e-mail to: editor.quest@iafrica.com or fax your communication to (011) 673 3683. Please give your full name and contact details.


fights TB

Genomics is revolutionizing the science of epidemiology and helping to custom-design public health policies that target TB in different places and circumstances. Eileen Hoal and Paul van Helden explain how the new technologies work for South Africa. uberculosis (TB) is a threat everywhere, even in rich first-world countries with superior public health services. A close correlation exists between wealth and TB incidence, and we know that public health provision – including delivery of food, clean water, housing, and good health care – is crucial for combating the disease. But we cannot at present raise wealth and living standards for everyone in all parts of the world, so we need new ways to fight TB. This is specially true in poorer countries, where conditions are different and solutions appropriate in the industrialized world may not work. Modern genomics technologies enable scientists to find out more about the details of the disease and its spread so that public health professionals can custom-design their policies to suit the situation on the ground. In South Africa, genomics is providing the kind of information that can help to control the epidemic better.

T

Above: A setting that’s a breeding ground for TB. Photograph: Erik Föster, www.peach.co.za

Lessons from history Around 1780 – During the early industrial revolution, TB is thought to have peaked in Western Europe: about 1.25% of the entire population died each year from TB (or ‘consumption’). Early 1800s – TB was so pervasive that 98% of the children in a typical English workhouse were infected. 1830 – Food production for the first time exceeded population growth and wages could now buy adequate food. This is important, as a person who is 10% underweight carries a threefold enhanced risk for developing TB. 1830+ – TB declined in Western Europe and the UK. The rapidity of the decline was most likely due to improvements in housing and working conditions once the miseries of the industrial revolution had been recognized. The decline of TB continued at a similar rate, despite the introduction of X-rays, sanatoria, sputum diagnostics, and even antibiotics, with only small, temporary increases noted in Europe during the two world wars. As microbiologist René Dubos remarked: “...magic bullets are not the most effective way to deal with pathogens...” and, commenting further on the decline in disease incidence, science writer Bernard Dixon observed that: “The real keys came from ecology, human behaviour and a recognition that microbial and human populations are part of the same evolving biosphere”.

▲ ▲

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TB in developing countries Country

Zimbabwe South Africa Kenya Mozambique Ethiopia Uganda Democratic Republic of Congo India Russian Federation Brazil

Total population (millions)

Genome variability No. of TB cases per 100 000 of the population

Global ranking by estimated total no. of TB cases

Estimated TB cases of adults (age 15–49 years) who are HIV+ (as % of total TB cases)

12.627 43.309 30.669 18.292 62.908 23.300

584 526 481 433 397 351

21 9 12 19 6 17

67 60 49 48 42 35

50.948 1 008.937

320 184

11 1

24 4

145.491 170.406

132 68

10 15

1 3

South Africa has one of the highest TB disease rates in the world, exacerbated by the high incidence of HIV. By virtue of its large population, India has the greatest number of cases of the disease. (These data are drawn from the World Health Organization and other sources and they quote statistics as available during the period from 1997 to 2002.)

Epidemiology – the branch of medical science that aims to prevent disease by understanding better the concepts and mechanisms underlying the occurrence, transmission, and control of epidemic diseases. Genomics – the study of the total DNA of a cell Genotype – the nature and arrangement of genes in an individual organism Isolate – a pure culture of a microbiological specimen, representing a single strain Prophylactic – a medicine or procedure that helps to prevent disease (e.g. a vaccine)

Right: The rod-like M. tuberculosis seen after staining in routine diagnosis. Picture: Courtesy of Carmen Pheiffer

Some definitions

Questioning the dogmas Epidemiology* is a starting point for public health. Applying genomics* and molecular biology to epidemiology has created the new field of ‘molecular epidemiology’. Its novel and dramatic insights into TB are changing the way we think about the transmission of the disease. In the past, without tools to analyse the details of infection, it was assumed that if person A with TB came into contact with person B, and person B subsequently contracted TB, then person A had transmitted the disease to person B. In most TB cases, however, contact tracing fails because people engage with too many friends and strangers every day to know who could have infected them. So traditional epidemiology can’t identify where exactly TB transmission occurs. In addition, when so many TB patients either deny having any known contact with other TB cases or admit to having had contact with a TB case only many years before, the notion of latent (or ‘dormant’) disease arose. This gave rise to dogmas: for example, that multiple cases in one household confirm household transmission, or that isolated cases illustrate latent disease. Results from new technologies reveal, however, that some of these dogmas may not always be correct.

Before the birth of genomics there was already evidence of some variability in Mycobacterium tuberculosis (known colloquially as ‘Mtb’ ), the bacterium that causes tuberculosis. New tools that can genotype accurately any isolate* of Mtb mean that we can investigate, more thoroughly than before, issues such as: ‘how variable is the genome of Mtb ?’ and ‘how stable is it?’ Genotyping tools show that the genome is conservative in some ways and surprisingly variable in others, such that thousands of individual strains of Mtb exist. These genomes are relatively stable, fortunately, so DNA typing (or ‘fingerprinting’) can help to trace individual strains as they move through a population of TB patients. Clearly, then, if two TB patients known to each other have the same strain of Mtb, one must have infected the other, or they must have been infected by a common source (or ‘contact’). This knowledge can be used to answer further important questions.

What is the TB source? The TB epidemic has two major components: first, those individuals who are infected and rapidly progress to active disease (within two years of infection) and, second, those who were infected some time earlier (perhaps even decades earlier) in whom the latent disease is at some stage reactivated. Public health measures to deal with the epidemic must consider both components, and be designed in the right way where the epidemic is heavily biased towards one or other. So it is important to estimate the relative proportion of these two components, particularly because, traditionally, much of the epidemic was thought to be from the reactivation of latent disease. Using molecular tools, researchers compare genotypes* of Mtb isolates* and summate those with identical fingerprints. They then calculate their estimate of transmission as the proportion of matched isolates compared to the total number. It was found that most TB cases in first-world cities such as San Francisco and London are isolated and from reactivation TB (as the dogma suggests). Therefore, prophylactic* treatment of those in contact with TB cases as well as those identified with latent TB is probably costeffective and can reduce the burden of disease substantially. In cities in the developing world, however, such as Cape Town, we find that probably about 80% of TB cases result from recent transmission, so the public health policies and measures needed here are very different.

* An asterisk following a term indicates that it is defined in the definitions box on this page.

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Where does transmission occur?

What drives drug-resistant TB?

800 700 600 Pulmonary

500 400 300 200 100 0 <1

10–14

25–29 40–44 Age group (years)

55–59

70+

The incidence of TB among people in the Western Cape in terms of age group. Note in particular the high incidence among children up to the age of about 6 years and, after a decline, the steep rise in incidence from the age of 15 years.

DST–NRF Centre of Excellence for Biomedical TB Research Tuberculosis (TB) has been declared a national health emergency. The only hope for eradicating this devastating disease is a quantum leap in the quality of tools for diagnosing, preventing, and treating it. Advances in genomics and the molecular biosciences create unprecedented opportunities to investigate the biology of Mycobacterium tuberculosis and its interaction with its human and animal hosts. The two laboratories making up South Africa’s Centre of Excellence (CoE) for Biomedical TB Research contribute significantly to global research efforts for controlling TB. The Wits/National Health Laboratory Service component, under the directorship of Professor Valerie Mizrahi, conducts fundamental research in mycobacterial metabolism that aims at identifying, validating, and characterizing new drug targets and vaccine candidates for TB. The Stellenbosch University component, whose director is Professor Paul van Helden, bridges the gap between basic research and its application in clinical TB research and management. The CoE follows a multidisciplinary approach to the problem of TB. Its extensive, collaborative clinical research network – essential for success in applying post-genomic research findings to infected people and animals – also provides a powerful platform for training young scientists in state-of-the-art health research. For more visit www.nrf.ac.za/centres (DST–NRF Centres of Excellence).

been designed on the basis of this information, the extremely dangerous outbreak could be controlled. Now that we know the mechanisms of drug resistance and the genes involved, faster diagnostics can and have been developed, which should help us to combat the emergence of drug-resistant TB. ▲ ▲

Resistance to antibiotics is a major problem in TB, as in all infectious diseases. Researchers can identify drug-resistant strains by DNA typing, and also by DNA sequence analysis of genes that are known to be involved in drug resistance. It was traditionally assumed that, if a person presents with TB that is resistant to antibiotics from the outset, then a drug-resistant strain was transmitted to that person (this is called ‘primary resistance’). If, however, the person has had a previous episode of TB, it was assumed that drug resistance was acquired (that is, that the strain of Mtb had developed resistance from the patient’s exposure to the drugs). Surveys of drug resistance are regularly conducted and reported under the auspices of the World Health Organization (WHO). Often we’re told that, in all settings, ‘primary resistance is much lower than acquired resistance’, so we might conclude that acquisition of resistance is the major driver of drugresistant cases of TB. In the South African setting, however, this is not true. Although the results of traditional surveys follow the WHO interpretation, results coming from molecular tools suggest that, in South Africa (certainly in the Western Cape), most drug-resistant TB results from transmission. In some ways this is good news, as it suggests that most new cases are not due to poor treatment. But it also shows that we are not stopping transmission of drug-resistant strains to new patients. We need new policies and practices to address this problem. In New York in the 1990s, for example, the use of molecular techniques revealed a major outbreak of a particular multidrug-resistant strain of TB. Once extensive public health efforts had

Western Cape Incidence rate per 100 000

It makes sense to assume that, since people spend a lot of time at home, it is easy to acquire TB from an infected person in that household. This often happens and it’s a clear risk factor in first-world countries, where prophylactic treatment is often advised for family members. But the situation is quite different in South Africa. Even though we do detect transmission in households, some 80% of cases are in fact transmitted away from home. Thus, the costeffectiveness of prophylactics for family members needs to be considered more carefully in our setting, and this method will certainly have far less impact on the disease in South Africa than in the developed world.

Left: Mtb growing in an experimental medium, in a procedure used for research or to confirm diagnosis. Picture: Courtesy of E. Engelke

Other Mycobacteria Knowing the genomes of Mycobacteria has allowed us to develop species-specific genomebased identification procedures that could influence treatment for HIV-infected individuals as well as veterinary practice. ■ Infants born HIV-positive and vaccinated with the attenuated Mycobacteria bovis strain BCG, for example, can develop disease mediated by BCG. It’s important to identify the species type quickly, as treatment of Mtb is different from that of M. bovis BCG infection. ■ M. africanum is common in parts of Africa, but we don’t know if so-called bovine TB (M. bovis), which can infect animal species such as sheep, goats, and cattle all over the world, commonly infects individuals in Africa or South Africa. The new methods make it possible to investigate species-specific TB disease.

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What causes repeat episodes? Despite antibiotic therapy, many TB patients – especially those who default on treatment – experience a further episode of TB. Not surprisingly, in the absence of suitable investigative tools, it was assumed that these were relapses caused by failure to cure. DNA typing, however, shows that – particularly in high incidence settings – this assumption is false and that most cases are due to infection with a new strain of TB. It has also shown that the risk of progressing to active disease is much greater for someone infected for a second or subsequent time than it was the first time around. This increased risk has major implications for interpreting drug or vaccine trials and for designing vaccines and vaccination procedures. ■ The authors are in the MRC Centre for Molecular and Cellular Biology and the DST–NRF Centre of Excellence for Biomedical TB Research, and based in the Division of Medical Biochemistry, Faculty of Health Sciences, University of Stellenbosch, PO Box 19063,

Tygerberg 7505. Senior researcher Professor Hoal has studied aspects of TB for the past 12 years. Paul van Helden has worked in TB research for over 15 years. He is professor and head of Medical Biochemistry at the University of Stellenbosch, the director of the MRC Centre, and a co-director of the DST–NRF Centre. For more, visit http://academic.sun.ac.za/med_biochem/index.html as well as the World Health Organization at www.who.int/tb/en; the International Union Against TB and Lung Disease at www.tbrieder.org; and the Global Alliance at www.tballiance.org For articles in the scientific literature, visit the National Library of Medicine web site www.nlm.nih.gov Of particular interest are the following: A Van Rie et al., “Exogenous reinfection is a common cause of tuberculosis recurrence after cure”, New England Journal of Medicine, vol. 341 (1999), pp.1174–1179; S. Verver et al., “Transmission of tuberculosis in a high incidence urban community in South Africa”, Journal of Epidemiology, vol. 33 (2003), pp.351–357; S. Verver et al., “Proportion of tuberculosis transmission that takes place in households in a high incidence area”, Lancet, vol. 363 (2004), pp.212–214; and E.M. Streicher et al., “Genotypic and phenotypic characterization of drug-resistant Mycobacterium tuberculosis isolates from rural districts of the Western Cape Province of South Africa”, Journal of Clinical Microbiology, vol. 42 (2004), pp.891–894. For a recent suite of articles on pathogen genomics, see the South African Journal of Science, vol. 100 (2004), pp.451–482. For a one-page “Understanding DNA” Fact File, see QUEST 1(3), p.25 (available with other QUEST information on www.assaf.co.za).

Understanding the TB bacterium Defeating TB means knowing how the disease works and how the bacterium survives and grows in the body of infected persons and animals. Bavesh Kana and Valerie Mizrahi describe intricate laboratory work that’s needed for developing better treatments. Tackling the TB problem

human population. The HIV pandemic increases the disease burden greatly, owing to the increased risk of developing primary and post-primary TB. Furthermore, the public health threat of TB has become worse through the emergence of multidrug-resistant (MDR) TB, caused by strains of Mtb that have developed resistance to more than one of the first-line drugs used to treat it. MDR TB is difficult and costly to treat, so it has a high mortality rate. We need most urgently to develop better tools for diagnosing, preventing, and treating this ravaging disease. To design new ways of defeating it, we have to understand very thoroughly the mechanisms Mtb uses to infect its human host – how the bacterium replicates and causes disease and how it can persist for prolonged periods of ▲ ▲

Mycobacterium tuberculosis (colloquially known as Mtb), the bacterium that causes tuberculosis (TB), is the deadliest of all bacterial pathogens. Every year it kills more than two million people and is responsible for more than eight million new cases. Its power to survive in humans is extraordinary. About one third of the world’s population – some two billion people – is infected with Mtb asymptomatically (that is, they are infected but display no symptoms – the infection is ‘latent’). Latently infected individuals with healthy immune systems carry a 5–10% lifetime risk that the bacteria will reawaken, leading to full-blown (‘post-primary’) TB. So society clearly faces a massive burden of future disease from infections that already exist in the

Pictures: Courtesy of the MMRU

Left: In a petri dish, blue TB colonies after the insertion of the plasmid with the blue marker gene (see diagram on p. 8).

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Right: The GenePix scanner that produces high-resolution microarray scans. Below: Targeted gene knockout. A small circular DNA molecule (plasmid) carries two genes: the first, a nonfunctional mutated copy of the gene of interest (‘mutated gene’); the second, a ‘marker gene’ (here, a gene that turns the bacterium blue if a particular chemical indicator is present). When this plasmid enters the wild type bacterium the bacterium turns blue, indicating that the plasmid has been successfully inserted. Once inside the bacterium, the mutated gene aligns itself with the functional gene in the bacterial chromosome. Enzyme systems in the bacteria then switch the functional copy of the gene in the chromosome with the non-functional mutated gene in the plasmid. Not having the signals necessary to remain in the organism, the plasmid is ejected after the geneswitching event and, in this way, a knockout mutant strain of the bacterium is produced.

ed at ut M ne ge

Marker gene

This method was developed in the UK and refined and applied further by Bhavna Gordhan, Stephanie Dawes, Edith Machowski, and others in the MMRU.

Plasmid

time in an asymptomatically infected individual. A new era of TB research began when, in 1998, the groups of Stewart Cole (of the Pasteur Institute in Paris) and Bart Barell (of the Sanger Centre near Cambridge) completed the genome sequence of a laboratory strain of Mtb and, in 2002, the sequence of a clinical isolate was completed by another group in the USA. These developments moved Mtb from the backwaters of microbiology – where it had languished for decades under the misguided notion that TB could be eradicated with the available drugs – to its forefront. The explosion of genome sequence information on other bacteria – including close relatives of the TB bacillus, such as Mycobacterium leprae (the agent that causes leprosy) – meant that similarities and differences between Mtb and other bacteria could be revealed. Genomic comparisons have helped to expose some of the workings of Mtb and its evolution. The functional classification of the 4 000-odd genes comprising the genome of Mtb yielded invaluable information and intriguing clues about the metabolic repertoire of this organism, but the full power of this new knowledge began to be realized when it was applied with other tools, such as gene knockouts and DNA microarrays. The advent of genomics and its coupling with powerful new technologies changed the face of TB research. It created optimism in the ability of science to deliver new and improved TB bacterium ways to control this devastating disease.

Gene knockout

Wild type bacterium Functional gene Bacterial chromosome Gene switching

Plasmid ejection Knockout mutant strain Non-functional gene Bacterial chromosome

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To understand the metabolism of the tubercle bacillus we need to conduct genetic experiments. Historically, it’s been difficult to manipulate members of the genus Mycobacteria (to which Mtb belongs): scientists lacked the right vehicles (or ‘vectors’) for delivering DNA into these organisms for experimental purposes. The past decade, however, has brought dramatic advances in techniques that can be used for identifying and understanding the genes responsible for the TB

bacterium’s growth. As a boxer might knock an opponent out in a ring, so scientists use ‘gene knockout’ as a powerful technique for, literally, ‘knocking out’ a gene in order to disrupt its functioning. This leads to the loss of the protein encoded by that gene. In a gene knockout, manipulated DNA is inserted into the normal (or ‘wild type’) bacterium so as to disrupt the functional DNA encoding for a specific gene in some way. The result is a new ‘knockout mutant’ strain of the bacterium created in the laboratory: the researcher can learn about the function of the gene that was disrupted by assessing this mutant and comparing it with the wild type. For example, if researchers disrupt a gene that encodes a function that’s essential for growth, the mutant form of the bacterium in which that particular gene is disrupted cannot survive (that is, it is not ‘viable’). This type of information is immensely valuable, since genes that encode proteins essential for growth or survival may become good targets for attack by new drugs. This type of approach for understanding better the physiology of Mtb will ultimately help scientists to identify new drug targets and to develop new vaccines. Random gene knockouts Gene knockout strains can be created in a targeted or an untargeted way. One untargeted (or ‘random’) method relies on the use of mobile genetic elements, called transposons, which are able to insert themselves, at random, into the genome of an organism. When a transposon inserts itself into a gene, it disrupts the function of that gene. The ability to insert randomly means that a transposon can randomly knock out any gene (unlike a targeted approach, which requires one to have a selected target gene to knock out). Random insertion, therefore, means that the transposon can, in theory, knock out any gene, or it can create a mixture of bacteria where each bacterium has a different gene knocked out. In this way, researchers are able to create an entire library (or ‘pool’) of mutants. In the past, to study gene function, scientists had to examine each gene individually – using a ‘one gene at a time’ approach. Studying the 4 000-odd genes in the TB bacterium in this way would take an impossibly long time. Now, in the era of the genome, the ability to create pools of mutants means that researchers can use a new ‘parallel processing’ approach, allowing many genes to be studied at the same time. To decipher the information captured by the use of transposons, Eric Rubin and his team at the Harvard School of Public Health in Boston


developed an ingenious method known as ‘TraSH’ (‘transcription site hybridization’). This is an excellent example of functional genomics, as it allows researchers to identify simultaneously all the genes of Mtb that are essential for its growth under the particular conditions being tested (for instance, in a laboratory culture or in the organs of an infected animal). Targeted gene knockouts We use a targeted approach to investigate the function of any one particular gene of interest. Our laboratory has actively been applying methods for targeted gene knockout in Mtb. Using this technology, we have created dozens of knockout mutants of Mtb, which are being used to study particular aspects of the biology of this pathogen. This type of laboratory-based TB research needs special care and poses technical challenges. First, the researchers need special facilities to protect them from risk of infection. Second, the TB bacterium is extremely slow-growing – under optimal growth conditions it divides only about once a day, so it takes as long as about 3–4 weeks for colonies of Mtb to become visible on an agar plate. (Contrast this with the workhorse of bacteriology, Escherichia coli, which divides every 20 minutes or so and forms colonies overnight!) As a result, it typically takes 3–4 months to make and confirm a knockout mutant of Mtb. Once made, the mutant must be characterized so that researchers can assess the effect of the gene knockout on the behaviour of the bacterium – including its ability to grow in culture or in an animal model of TB, its ability to survive under stress, and its ability to start growing or ‘replicating’ after months or years in a latent state.

genome structure between different strains or isolates of an organism. In this gridded format, total DNA from the strain being analysed is compared to the set of genes from the reference strain imprinted on the chip. (For instance, this technology allows a mutant bacterium to be compared to a wild type.) Using this approach, US researchers have identified genes present in reference strains of Mtb (those whose genomes were sequenced), but which have been lost in certain clinical isolates that were cultured from TB patients. This information could be useful to identify those genes that are important for the transmissibility and virulence of the TB bacterium in humans. In another important application, DNA microarrays can be used to capture the ‘expression status’ of all genes in the organism simultaneously, that is, to record all at once which genes are ‘switched on’ (and to what level) and which are ‘switched off’. (A gene that is switched on enables the protein that it encodes to be made – remember, genes encode proteins – whilst a gene that is switched off does not allow the corresponding protein to be made.) This type of analysis provides a very useful snapshot of the physiological state of the organism, such as a TB bacterium, in the experimental condition being investigated. Through this method, researchers have uncovered some of the stressresponse mechanisms that this pathogen has at its disposal to help it survive so effectively. In an impressive application, Helena Boshoff (a South African scientist working abroad), Clifton E. Barry III, and others at the National Institutes of Health in the USA used gene expression profiling to deduce the metabolic Mtb responses to stresses caused by drugs. These researchers assigned expression signatures to specific drugs and by doing so were able to discern the workings of possible new anti-TB compounds. ■

DNA microarrays

Professor Mizrahi, who has been involved in TB research for the past 12 years, is the director of the MRC/NHLS/Wits Molecular Mycobacteriology Research Unit (MMRU) and co-director of the DST–NRF Centre of Excellence for Biomedical TB Research. Dr Kana is a researcher in the MMRU and a member of the Centre of Excellence. He has worked in the field of mycobacterial genetics and physiology for 7 years. Both authors are in the School of Pathology, University of the Witwatersrand and National Health Laboratory Service, PO Box 1038, Johannesburg 2000.

In a DNA microarray, a copy of each gene in a particular organism (in our case, each gene in the TB bacterium) is arrayed in a gridded format onto a small glass slide to produce a ‘gene chip’. (The scale is minute: a large dust particle, for instance, would obscure as much as onefifth of the picture.) Gene chips can be used, for example, in genome-wide comparisons to detect differences in

Left (above): M. tuberculosis (Mtb) is an aerosol-borne Class III pathogen – that is, it is transmitted through the air and can be inhaled. To eliminate the danger of working with this organism, researchers need specialized clothing and Biosafety Level III laboratory facilities. Such facilities are expensive to construct and maintain, and specially trained personnel are needed to operate them. Left (below): Part of a DNA microarray. This gene expression snapshot of Mtb was obtained under conditions of nutrient starvation, modelled on those that the bacterium may encounter when infecting a human host. A culture of Mtb was nutrient-starved and messenger RNA was processed for DNA microarray analysis. Red spots denote genes of Mtb that are switched on under nutrient-starved conditions; green spots denote those genes that are switched off; yellow spots denote genes that are unaffected by starvation. This whole-genome microarray of Mtb was printed by Sally Walford and Digby Carter (Microarray Facility, UCT); the slide was produced by Bhavna Gordhan (using the microarray scanner in the School of Pathology, National Health Laboratory Service and University of the Witwatersrand). For details consult H.I.M. Boshoff, Michael B. Reed, Clifton E. Barry III, and Valerie Mizrahi, “DnaE2 polymerase contributes to in vivo survival and the emergence of drug resistance in Mycobacterium tuberculosis” in Cell, vol.113 (2003), pp.183–193; S.T. Cole et al., “Deciphering the biology of Mycobacterium tuberculosis from the complete genome sequence” in Nature, vol. 393 (1998), pp.537–544; B.D. Kana and V. Mizrahi, “Molecular genetics of Mycobacterium tuberculosis in relation to the discovery of novel drugs and vaccines” in Tuberculosis, vol. 84 (2004), pp.63–75; and for reports on the method used to create a knockout, see T. Parish and N.G. Stoker, “Use of a flexible cassette method to generate a double unmarked Mycobacterium tuberculosis tlyA plcABC mutant by gene replacement” in Microbiology, vol. 146 (2000), pp.1969–1975. Visit these web sites for more on TB: www.tballiance.org (The Global Alliance for TB Drug Development); http://genolist. pasteur.fr (The Tuberculist Worldwide Web Web Server); www.tigr.org/tigr0scripts/ CMR2/CMRHomePage.spl (The TIGR Comprehensive Microbial Resource); www.niaid.nih.gov/dmid/genomes/pfgrc

and http://pfgrc. togr.org (NIAID Pathogen Functional Genomics Resource Centre); www.sanger.ac.uk/Projects/Pathogens (The Wellcome Trust Sanger Institute, Pathogen Sequencing Unit); www.wits.ac.za/ myco (The MRC/NHLS /WITS Molecular Mycobacteriology Research Unit); www.aca demic.sun.ac.za/med_biochem/index.html (The MRC/SU Centre for Molecular and Cell Biology).

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Darren Martin explains how genomics helps scientists to understand HIV and why the rapid evolution of this virus makes vaccine development so difficult.

Why it’s so hard to combat AIDS ‘

G

transmissions of different HIV types (called HIV2A, HIV-2B, HIV-2G, HIV-1N, and HIV-1O). These have all resulted in small distinct epidemics, mostly confined to West Africa. Although only HIV-1M seems responsible for the global AIDS pandemic, researchers realized soon after the first few partial HIV-1M genome sequences were determined that they were ▲ ▲

enomics’ became a household word when the first human genome sequence was announced. The mainstream press popularized it in response to sensationalized debates on the potential benefits and hazards of such knowledge. All the word really means, however, is ‘the study of complete genomes’. Studying the genomes of organisms like the human immunodeficiency virus (HIV) is something that scientists have been quietly doing since the early 1980s. HIV genomics has enabled the development of HIV drugs and will, we hope, help us design an effective vaccine against HIV.

What genomics says about HIV Until relatively recently, all the genomes analysed have been those of small viruses. For example, the genome of HIV is nearly 300 000 times smaller than that of humans. Whilst only a single complete human genome has been sequenced, the HIV genome is so small that scientists have been able to determine the sequences of more than 400 full-length genomes. HIV and other virus genomes have contributed greatly to the understanding and control of viral diseases. Analysing HIV genome sequences has revealed much about the origins of the global AIDS epidemic and how similar epidemics might occur. It has been determined, for instance, that HIV-1M, the group of viruses primarily responsible for more than 99% of worldwide HIV infections, most likely originated from a single ancestral virus that was transmitted from a chimpanzee to a human sometime around 1930, somewhere in equatorial West Africa. We now also know that there have been other cross-species transmissions of HIV and HIV-like viruses, both among different primate species and among primate species and humans. Besides the 1930 transmission event that triggered the global AIDS epidemic, there have been at least five other independent primate-to-human

Subtype C ancestor

Group M ancestor

Subtype C isolates from India Subtype C isolates from South Africa Movement of HIV into India Movement of HIV into/out of South Africa

Subtype C

Other group M subtypes

HIV’s strategy is to be a super-mutator, able to survive for long periods within humans. Frequent mutation ensures that the virus remains constantly one step ahead of our immune systems and establishes itself in different forms in different populations. Changing its physical characteristics whenever they are detected by the immune system is key to the virus’s success.

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Pictures reproduced courtesy of the South African Journal of Science. Above: N. Prabdial-Sing (National Institute for Virology). Below: G. Lecatsas (University of Limpopo, formerly Medunsa)

Right: Thin-section electron micrographs of lymphocyte cultures showing HIV-1 particles. The mature virus, with a dense central core, accumulates at the plasma membrane of infected cells. Cell lines were infected with HIV for two days before harvesting. The sections were stained with lead citrate and uranyl acetate and viewed in a transmission electron microscope. The virus particles are approximately 100 nanometres in diameter.

dealing with something extraordinary. They found great variability in the sequences of viruses obtained from different patients. Unlike other known virus epidemics, it seemed that AIDS was being caused by a large group of distinct strains. We now know that the actual number of HIV-1M strains is huge, and is only slightly less than the number of HIV-infected people. This means that virtually every HIVinfected person has a unique strain of the virus. To understand how so many different HIV strains have arisen in the short time since the virus first infected humans, we first need to understand a bit about HIV’s survival mechanisms.

Viral survival

HIV vaccine targets Three promising approaches being used to protect people against large groups of HIV strains are targeting vaccines ■ against the most important working parts of the virus ■ against many small pieces of the virus that are known to stimulate strong anti-HIV immune responses ■ at artificial theoretical ancestral or ‘consensus’ virus strains that are more closely related to real circulating virus strains than the real strains are to one another.

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HIV has become adapted to long-term survival in an extremely harsh environment. Our immune systems are a brutally efficient defence against the viruses that try to invade our bodies. Most cold or flu viruses. for example, only manage to gain a momentary foothold in our bodies before our immune systems destroy them completely. To live, these viruses must be transmitted to another person within days of infection. Their survival depends on being able to move between people within the microscopic droplets of saliva that infected people sneeze and cough into the air and onto surfaces. HIV’s mode of transmission is a lot less sophisticated than that of so-called airborne viruses. It passes from one person to another by direct contact of body fluids. The key to HIV’s success is, therefore, to survive the massive onslaught of an immune system for long enough to be transmitted to an uninfected person, normally during sexual intercourse. HIV’s existence is dominated by the constant threat of destruction by our immune systems. The virus produces proteins that confuse and mislead our immune systems and it actively kills the cells that we normally rely on to defend us against viruses. Most important, HIV adapts very rapidly to whatever effective immune defences we are capable of mounting. This adaptive

ability is what causes the great HIV-1M variability found worldwide. Since it first entered humans 70 years ago, the virus has undergone a vastly accelerated form of evolution – similar in extent to that which yielded humans, chimpanzees, gorillas, and orangutans from an ancestral great ape. Unlike the evolution of humans from apes, however, there has been no real long-term progression in the evolution of HIV. Within an infected human, virtually all the short-term evolutionary advances the virus makes provide it with absolutely no benefits once it is transmitted to another person. While this lack of evolutionary progression does not benefit the virus directly, the huge number of HIV strains that this type of evolution has generated presents us with a formidable problem.

Vaccine development Our best chance of containing the AIDS epidemic is the widespread use of an effective HIV vaccine. In the past it has been relatively easy to produce vaccines to protect people against one or several strains of a virus. It will be incredibly difficult to produce a vaccine that will protect people from infection with the countless number of different HIV strains that currently exist. In most parts of the world, most HIV infections are caused by groups of related strains known as ‘subtypes’. Virtually all infections in North America come from a group of strains referred to as HIV-1M subtype B, for example, while more than 95% of infections in South Africa come from a strain grouping referred to as HIV-1 subtype C. Most HIV vaccines currently being developed or tested are intended to protect recipients from infections with strains that belong only to specific subtype groupings. Analyses of HIV genome sequences and the ways that human immune systems interact with different HIV strains show how vaccines might be constructed to minimize the chances of failure in the face of overwhelming virus variability.


Q Fact file

TB & HIV: Deadly alliance While the designs of the many HIV vaccines are much more sophisticated than those of other vaccines in widespread use, there is only the slimmest chance that any of them will prove anything like as effective as, for example, smallpox or polio vaccines.

Reason for hope Sophisticated analyses of HIV genome sequences aimed at studying the evolution of the virus within infected patients indicate that the virus is literally surviving on the brink of extinction. The extraordinarily high rate at which HIV is evolving is very close to the absolute maximum limit for an organism. The lack of progression in HIV evolution is a symptom of an underlying problem that occurs when evolution rates approach this maximum. Paradoxically, once an organism exceeds this limit, it encounters ‘mutational meltdown’ – a situation where, rather than progressively building a genome, evolution progressively decays it. While there may be up to 100 times as many individual viruses in an HIV-infected person than there are humans on earth, only between one and 10 out of every million of these ever produce descendents that survive the entire duration of an infection. Approximately 99.9% of viruses produce descendants that either get killed by the immune system, or are too evolutionarily damaged to function properly. HIV is on the brink of mutational meltdown because our immune systems have given it nowhere else to go. It could even be possible that all that an effective vaccine or drug needs to do is slightly to boost the anti-HIV efficiency of our natural immune defences. Human genomics is in its early infancy, with only one full-length sequence determined and the functions of the vast majority of the 40 000+ identified genes remaining unknown. HIV genomics is in its adolescence, with over 400 full-length HIV sequences determined, all its nine genes extensively studied, and the atomic structures of all its proteins determined. Yet, despite knowing more about how this virus works than we do about any other organism, we still don’t really know how to create an effective HIV vaccine or a cure. Simply knowing the genome sequence of an organism and how all its bits and pieces fit together does not tell us the whole story. Perhaps the most significant thing we’re learning from HIV genomics is that even the simplest organisms are complex beyond our present capacity to understand them fully. ■ Dr Martin contributes to the field of HIV vaccine development by using HIV genome sequences to study how HIV is evolving. He is in the Institute for Infectious Diseases and Molecular Medicine, Division of Medical Virology, Faculty of Health Sciences, University of Cape Town.

In 1992, Frank Ryan’s excellent popular book, Tuberculosis: The Greatest Story Never Told: The human story of the search for the cure of tuberculosis and the new global threat (Bromsgrove: Swift), summarized the scientific achievements that dramatically lowered the death rate from tuberculosis (TB) in the last century and alerted readers to the new, deadly alliance of TB and HIV/AIDS.

Successful cure and new threat The development of antibiotics brought down the numbers of deaths from TB – as well as new infections – in the developed world. 1953 In the US, 84 300 people contracted TB and 19 700 died of it. 1985 New US infections dropped to 22 200; deaths numbered 1 750. Late 1970s The first cases of AIDS were diagnosed. 1989–1990 In 1989, the number of new TB cases in the USA was up by 4% on the previous year; in 1990 it jumped up 9.4%. 1988–1991 In the UK, the number of new cases dropped till 1988, remained stable for two years, then rose by 5% in 1991 – the first time Britain had seen such a rise in 40 years. A worldwide resurgence of TB was reported, with a veritable explosion in subSaharan Africa. A 1991 article in The Lancet entitled “Is Africa lost?” warned that the sinister congruence of AIDS and TB was bringing to the world “the greatest public health disaster since the bubonic plague.”

How the alliance works AIDS is caused by infection with the human immunodeficiency virus (HIV), explains Ryan, which can remain dormant for a long time. It infects a type of human white cell (a type of T lymphocyte) that is important for the immune response of the human body to infection, and it kills monocytes, another key cell in the human defence system. The immune cells destroyed by HIV are also the ones that enable the body to fight TB. In those millions of people worldwide who, often without knowing it, still harbour the TB bacterium in latent or dormant form, these cells control the TB and prevent it from becoming active. In both TB and HIV, a person can be infected but clinically healthy for years after the initial infection. Before illness begins, the only signs of infection are, respectively, a positive tuberculin test and circulating antibodies (HIV positivity). By the early 1990s, US doctors saw that HIV was triggering full-blown TB in people whose TB was hitherto believed to be cured or inactive. They also observed the reverse cooperation. Not only was infection with HIV triggering a latent TB infection but, within a few months, the TB itself activated the HIV infection, causing it to blossom into full-blown AIDS. In effect, each disease was triggering the other so that, within months of becoming HIV positive, the patient – often unaware that she or he was harbouring the TB bacterium from childhood – went into a steep decline, with overwhelming infection from both diseases simultaneously.

The situation in 2005 The deadly synergy of TB and HIV/AIDS – often called the ‘co-epidemic’ or ‘dual epidemic’ – is worst in countries where, for instance, high numbers of children are infected with the TB bacterium and where the incidence of HIV is also high (see table on p. 4). Communities experience the result when young adults (from their mid-20s to their mid-40s or so), whose TB would remain under control for many more years if their immune systems were healthy, begin to die of TB in exceptionally high numbers. In such communities, HIV is among the greatest risk factors for TB. In 1993, the World Health Organization (WHO) declared TB “a global health emergency” and, in South Africa, it is officially a national emergency. We hope that researchers (such as those whose work features in this issue) will find ways to break the deadly alliance. According to the WHO: ■ An estimated one-third of the 40 million people living with HIV/AIDS worldwide have TB. ■ People with HIV are up to 50 times more likely to develop TB in a given year than HIVnegative people. ■ TB is a leading cause of death in HIVinfected people and kills up to half of all AIDS patients worldwide (most people infected with both diseases live in subSaharan Africa). ■ TB infection is currently spreading at the rate of one person per second. According to the 2005 Global Tuberculosis Control report: ■ Global TB prevalence has declined by more than 20% since 1990. ■ Incidence rates are now fairly stable in five of the six regions of the world: the glaring exception is Africa, where incidence rates have tripled since 1990 in countries with high HIV prevalence and are rising across the continent at a rate of 3–4% annually. ■ Four out of the six regions look set to reach the UN Millennium Development Goal of reducing TB incidence by 2015. The exceptions are Africa (with its TB/HIV coepidemic) and Europe (with its high levels of multidrug-resistant TB). ■ Since 1995, over 17 million people with TB have benefited from effective treatment.

What can individuals do? ■ Have an HIV test if you are at risk or know you have TB. ■ If you are HIV positive, be screened for TB immediately: TB can be cured, even in people living with HIV. ■ Take the drugs you are prescribed, regularly and without fail (to help prevent multidrug-resistant TB). Visit www.who.int/tb/wtbd2005/en and access the full Global Tuberculosis Control report for 2005 online. Consult B.G. Williams et al., “Patterns of infection: Using age prevalence data to understand the epidemic of HIV in South Africa”, South African Journal of Science, vol. 96 (2000), pp.305–312.

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Elephants in southern Africa, south of the Zambezi river, have recovered from a population low of a few thousand in 1900 to more than 200 000 today. What problems do they cause? What's the solution? The debate rages and David Cumming presents some of the concerns. igh elephant densities in protected areas are changing environments significantly, in ways that may reduce biodiversity. The dilemma for conservation authorities and the public is whether or not to contain, or even reduce, elephant numbers in national parks.

H

Evolving populations Hominids and elephants share a long evolutionary history in the African savannas, with anatomically modern humans appearing about 200 000 years ago. In the sense that humans and elephants can have enormous impact on their habitats, both species are ‘environmental engineers’.

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Understanding those impacts in an evolutionary way helps today’s debate on managing elephants in protected areas, because present-day human–elephant–plant interactions almost certainly bear little resemblance to those that existed in the millennia before about AD 1500, when human populations were a fraction of their current levels and elephants could range freely. What do we know about early human–elephant–habitat interactions? How true is the ‘myth of wild Africa’, where the land was supposedly untouched by humans? Two things are clear – when humans learned to use fire they had the means to manage

landscapes in a way that no other animal could do and hominids were superb predators. Once they developed stone tools and poison-tipped spears and arrows, elephants would have featured as prey. But the key question “Did human predation contribute to limiting elephant numbers in African savannas?” remains unanswered. It is clear from cave paintings that the San were hunting elephants a few thousand years ago. Archaeological and historical research reveals that ivory was traded for centuries from the east African coast. Between 1546 and 1881, annual exports from Isle de Moçambique amounted to about 135 tonnes, suggesting a sustainable harvest


100 years of successful elephant conservation By 1900, few elephants were left south of the Zambezi river and it was feared that they would become extinct in southern Africa. There are now more than 200 000 in the subcontinent – by any reckoning, an outstanding conservation success. Contributing to the extraordinary recovery of elephant populations in the region was the high level of protection

Left: Elephants in a mature Faidherbia albida woodland, Mana Pools National Park, Zimbabwe. Photograph: Tim Wellington

Above: San painting of an elephant, in Chikupu cave about 50 km north of Harare. Photograph: David Cumming

The elephant ‘problem’ The recovery of elephant numbers generated problems and conflicts. As elephant populations grew rapidly during the early 20th century, so too did rural human populations, so, by the 1930s and 1940s, crop-raiding by elephants had become a problem for peasant farmers. In Zimbabwe, for example, the human population grew from about 500 000 in 1900 to more than 12 million in 2000 and, during the 1950s, there was a 15% per annum increase in the number of elephants destroyed in areas surrounding Hwange National Park. Wildlife departments were tasked with what was ▲ ▲

from southeastern Africa. Worked ivory from archaeological sites in the Limpopo basin, particularly from Mapungubwe, reveal that ivory was traded in this region a thousand years ago. We have no good information on the size or density of elephant populations in southern Africa a thousand or even five hundred years back. But we do know that elephant numbers and the centuries-old ivory trade in southern Africa collapsed about 120 years ago through over-hunting.

given them by colonial governments. In Zimbabwe during the 1920s, for example, killing a cropraiding elephant needed the governor’s permission. Further protection came from an agreed Africa-wide ban in 1908 on the export of tusks of cows and calves. The high reproductive rate of elephant and low calf mortality resulted in population growth rates of about 5% per annum, with a doubling time of approximately 15 years. Elsewhere in Africa elephants fared less well. By the mid-1980s, the weight of ivory leaving the continent had risen to some 850 tonnes a year – the same level it had reached in 1880 before the ivory trade collapsed. The dramatic decline of elephants in East and Central Africa during the 1970s and early 1980s through illegal hunting and uncontrolled export of ivory resulted in elephants being listed on Appendix I of the Convention on International Trade in Endangered Species (CITES) in 1989. The listing effectively banned all international trade in elephants and elephant products until a partial downlisting to Appendix II in 1997, and it had major implications for the management of southern Africa’s still well-protected and burgeoning elephant populations.

Changes in elephant numbers in countries south of the Kunene–Zambezi rivers (1900–2000) Country Botswana

1900

2000

< 800

c. 120 000

Mozambique

< 500

c. 3 500

Namibia

< 500

c. 14 000

South Africa

150–200

c. 15 000

Zimbabwe

< 4 000

> 100 000

Total

< 6 500

c. 250 000

Examples of elephant impact on Zimbabwe's woodlands Sengwa Wildlife Research Area in the early 1970s (1 elephant per km2) ■ The proportion of dead trees in miombo, acacia, and mopane woodlands in 1972 averaged 32% (the range was 22–48%) ■ The proportion of trees converted to shrubs averaged 30% (range: 12–45%) ■ The decline in woody biomass in miombo woodland between 1974 and 1978 was estimated at 46.4% (23 023 kg to 12 585 kg per ha). Mana Pools National Park ■ Of 124 baobab trees monitored at monthly intervals over 4 years, 29% died as a result of elephant damage.

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An aerial photograph of the southern boundary of Mana Pools National Park taken in May 1996. The miombo woodland in the park, to the right of the fence that was erected in 1968, was removed by elephants and fire. The neighbouring unoccupied communal land with intact woodland (to the left of the fence) was largely free of elephants and subjected to early burns. Photograph: David Cumming

euphemistically referred to as ‘problem animal control’ and errant crop-raiding elephants were increasingly hunted down and shot. The meat from animals killed in control operations provided some compensation to villagers for their loss while governments retained the ivory. Within protected areas, elephant populations grew at about 5% per year with a doubling time of 12 to 15 years. Outside protected areas, elephant range shrank as rural populations and agriculture expanded, with elephants being displaced into protected areas.

The result was rapidly escalating densities of elephants within protected areas and increasing human–elephant conflict on park boundaries. By the early 1960s, the impact of elephants on woodlands in several national parks in the region became a concern. Studies revealed high mortalities of mature trees combined with minimal replacement of canopy trees. By then, elephant densities had reached or exceeded 1 elephant per 2.5 km2. In some habitats, opening the canopy encouraged grass growth, which in turn resulted in higher fuel loads and hotter fires causing further woodland damage. In the early 1970s, in Zimbabwe’s Chizarira National Park, for example, Brachystegia boehmii trees were ring-barked or felled by elephants at the rate of 21% per year. The outcome was that, in six years, elephants had removed the woodland over large areas of the park. Similar

Feeding and foraging ■ The elephant is a large, generalist herbivore. ■ Adult bulls may weigh as much 7 500 kg. The average weight of an elephant in a typical population is taken to be 1 725 kg. ■ Adults eat 50–150 kg of plant material a day. ■ During the wet season, elephants feed mainly on grass and, during the dry season, increasingly on woody plants – taking leaves, twigs, and even branches. ■ An adult bull may knock over as many as 1 500 trees in a year. ■ Elephants walk, on average, about 12 km a day ■ The pressure of their feet on the ground (in kg per cm2) is similar to that of a 5-kg dik-dik but, because elephants take relatively shorter steps, they trample a greater area per unit distance walked than smaller animals do.

How elephants affect species diversity ■ There are remarkably few studies on this important topic. ■ In the succulent thicket of the Eastern Cape, a 1994 study found that elephants and goats greatly reduced the diversity of Mesembryanthemum species. ■ In miombo woodland in the Zambezi escarpment, a 1994 study found reduced diversity in trees, birds (particularly arboreal birds), and ants in woodlands affected by elephants compared with adjacent intact woodlands. ■ In the Chobe river front, a 1995 study found no marked effects on bird species diversity where woodlands had been heavily affected by elephants. ■ A longer-term study (in 2004) of elephants and ecology of the Chobe river front also found little evidence of species loss resulting from marked changes in the structure and composition of the riparian zone.

effects occurred elsewhere in the Zambezi Valley escarpment in Zimbabwe and, by 1994, 88% of miombo woodland within protected areas had been severely affected. Culling started in Hwange National Park in 1965 and in Kruger National Park during 1967, followed by regular annual culls in several national parks in Zimbabwe where elephant numbers were considered to be too high. The tusks and hides were recovered while the meat was dried and sold to nearby communities. Tusks and hides supported local ivory carving and leather manufacturing enterprises. Substantial revenue also came from the safari hunting of elephants and more than 90% of the revenue earned in Zimbabwe’s CAMPFIRE programme* came from elephant trophy hunting. Safari hunting of elephants also developed in Botswana. Countries in southern Africa responded in different ways to the ‘elephant problem’. Zimbabwe continued culling until the late 1980s. The Kruger National Park culled annually until 1994. Namibia conducted a single pre-emptive cull during a drought year in Etosha National Park, where the population has grown slowly and appears to be regulated by anthrax. Botswana did not cull at all. In Mozambique, populations were greatly reduced during the 20 years of civil war (1974–1994). In retrospect, the region’s countries provided what were in effect largescale experiments in managing elephants, from which we can draw useful conclusions. • Elephants are remarkably robust and in several parts of the region they recovered rapidly. The only protected sub-population to become extinct was the very small herd in the Tsitsikamma forest, near Knysna. Southern Africa now has at least six separate populations larger than 5 000 animals (one population exceeds 150 000). Elephants are clearly no longer an endangered species in the region. • Controlled harvesting of elephants and the legal ivory trade did not prejudice elephant conservation in southern Africa. • No elephant populations or ecosystems have collapsed, either as a result of culling or from nonintervention strategies. • Elephant populations at densities greater than 1 per 2 km2 where rainfall is low reduced some types of woodland to shrubland over large areas. Where elephant ranges were

* The CAMPFIRE programme was set up to benefit local communities who bear the costs of living with wildlife.

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not confined by fences, however, impacts on vegetation seem to have been less marked. • Trophy quality has been maintained, if not improved, in safari hunting areas.

What now? The Kruger National Park suspended culling in 1994, since when the elephant population has nearly doubled. If southern Africa does not contain elephant population growth, we can expect to have 400 000 elephants in southern Africa by 2020. This scenario would amount to carrying out a single large-scale experiment across the entire elephant range of the subcontinent. The current debate centres on three main areas of concern: the ecological impacts of elephants in ecosystems, the socio-economic effects of alternative choices about elephant management, and the moral and ethical issues related to killing elephants. Ecological impacts of high and increasing elephant densities. A central question is “What impacts will the continued growth of elephant populations have on plant and animal communities and the conservation of biodiversity in areas that have a legal mandate to conserve biodiversity?” A corollary is “What are the long-term impacts on ecosystem processes, resilience, and ultimately on biodiversity, of curtailing or reducing elephant population numbers?” The paradigms guiding ecological research and the management of parks have evolved over the last 40 years. Early on it was believed that nature naturally preserved a state of balance or equilibrium. Now we hold the more dynamic view that ecosystems are in a continual state of flux both spatially and temporally. They are complex, adaptive systems that may shift between alternative stable states – as, for example, between grassland and woodland, depending on fire, herbivory, and the influence of external drivers such as rainfall. In keeping with this paradigm shift, the Kruger National Park has taken the lead in embracing a paradigm of managing for heterogeneity. The evidence regarding effects of increasing elephant densities on ecological processes and biodiversity is interpreted in different ways. One argument claims that the present rise in elephant populations is simply a return to earlier conditions and part of longer-term spatial and temporal dynamics, but it takes no account of the extent to which humans and

livestock now dominate the region and where wildlife forms only about 10% of the total large herbivore biomass. Furthermore, the ecological impacts of containing elephant population eruptions have also not been examined critically. We urgently need experimental research in the study of elephant–habitat interactions. Economic and social consequences of unrestricted elephant population growth. The social and economic consequences of alternative elephant management strategies have been almost entirely neglected. Key questions include “What social and economic benefits are being lost by communities, land owners, countries, and the region by not harvesting elephants on a sustainable basis?” “What are the opportunity costs of allowing unrestricted growth of elephant populations?” Or, alternatively, “What are the benefits and costs of differing management strategies for elephant?” These are not trivial questions. A harvest of 5 000 elephants from a population of 200 000 elephants could generate US$40 million a year – enough to protect and manage 200 000 km2 of protected area at a rate of $200 per km2. National parks in Mozambique and Zimbabwe are currently operating on budgets as low as about $5 and $10 per km2, respectively. Moral, ethical, and humanitarian values regarding animal rights and the rights of elephants. Is the killing of sentient mammals such as elephants morally right and defensible in the 21st century? Alternatively, is it morally right to deny rural communities and land owners in Africa the right to kill and use elephants and their products to better their lives and, in so doing, maintain wild land in the face of pressures from expanding agriculture or other land uses? Or, is it wrong for national parks and protected areas to maximize economic returns from elephants so as to conserve better a full range of biodiversity within the protected areas for which they are responsible? The ecological and economic questions can be examined and analysed scientifically. But, ultimately, management decisions have to do with public choice, governed by the worldviews and the values of those who influence and take decisions. Science can, nevertheless, contribute to the moral and ethical debate through research on such matters as sentience in non-human animals, or the effects of alternative management regimes and actions (or lack of them) on stress and suffering in the animals or animal

Ground photographs, taken in November 1994, show the contrast between the vegetation on either side of the fence line on the southern boundary of Mana Pools National Park. The miombo woodland (above) was in an area largely free of elephants and the picture below was within the park. (See aerial photograph opposite.) Photographs: David Cumming

populations concerned. In considering what’s involved in conserving and managing elephant populations, we’re no longer dealing simply with managing the numbers of a single species. We are instead dealing with a complex social-ecological system at scales that range from the local habitat patch and rural household to the international platform. The science involved spans many disciplines and cultures – from normal hypotheticodeductive ‘hard’ science, to inductive and more inclusive science, and the multidisciplinary integration of science into the political arena. ■ Dr Cumming has been involved in elephant conservation and management since the mid-1960s. Formerly Deputy Director in Zimbabwe’s Department of National Parks and Wild Life Management and Programme Director for WWF’s Southern African Regional Office, he now works as an independent scientist and is a research associate at the Tropical Resource Ecology Programme at the University of Zimbabwe. For more, read J.C. du Toit, K.H. Rogers, and H.C. Biggs (eds.), The Kruger Experience: Ecology and management of savanna heterogeneity (Washington: Island Press, 2004); P.A. Jewell, S. Holt, and D. Hart (eds.), Problems in Management of Locally Abundant Wild Mammals (New York: Academic Press, 1981); D.H.M. Cumming, M.B. Fenton, et al., “Elephants, woodlands and biodiversity in southern Africa”, in South African Journal of Science, vol. 93 (1997), pp.231–236; C.Skarpe, P.A. Aarestad, et al., “The return of the giants: ecological effects for an increasing elephant population”, in Ambio, vol. 33 (2004), pp.276–282; and D. Western and D. Maitumo, “Woodland loss and restoration in a savanna park: a 20-year experiment”, in African Journal of Ecology, vol. 42 (2004), pp.111–121.

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How can we get rid of congestion that frustrates us every day? From Sarma Yadavalli, Kris Adendorff, Gert Erasmus, and Yegna Narayanan comes a mathematical solution.

e wait in traffic queues for lights to turn green and in supermarket queues to pay for purchases. We experience queues and congestion whenever the supply of a service doesn’t keep up with the

W

Queuing theory applications The Danish engineer and probabilist, Agner Erlang (1878–1929), was employed by the Copenhagen Telephone Company. Applying probability theory to telephone call traffic, he developed the foundations of queuing theory and derived a formula for loss and waiting time that was soon used by telephone companies in other countries. Since then, in service situations in which a limited number of servers provide for customer needs, queues have been intensively investigated wherever waiting line problems arise. Queuing theory applies to a great range of queuing systems in business and industry, such as ■ commercial service stations (e.g. banking services, appliance repairs) ■ transportation service systems (e.g. motor vehicles at traffic lights, trucks needing to be loaded or unloaded) ■ materials-handling, where material-handling units (servers) move loads (customers) ■ maintenance, where maintenance crews (servers) repair machines (customers) ■ inspection stations, where quality controllers (servers) inspect items (customers) ■ machines (e.g. computer facilities) that are viewed as servers whose customers are the jobs being processed ■ social services (e.g. in the judiciary and healthcare). Queuing problems can be behavioural, statistical, and operational, and systems are designed in particular to optimize service or to control it.

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demand. To tackle this problem, researchers have investigated the nature of queues and how to cope with them.

How queues form What happens to create a queue? People may arrive at a cinema ticket window, for example. If they arrive too many at a time, they either have to wait before getting their tickets or do without. If they choose to wait – and want to avoid chaos – they need to form a queue (sometimes called a ‘waiting line’) to maintain discipline and make sure that people take their turn. If too few people arrive, the situation is reversed – the person issuing tickets waits and remains idle till more people turn up. In these circumstances, the arriving people are called ‘customers’ and the person issuing the tickets is called a ‘server’. In another situation, too many documents, such as letters, may arrive all at once at a secretary’s desk for processing. Here, the letters represent ‘customers’ and the secretary represents the ‘server’. Or, where a machine breaks down, the broken machine represents a customer calling for the service of a person to repair it. These examples show the term ‘customer’ used in various ways. They also show that a service may be

performed either by moving the server to the customer or the customer to the server. Queues or ‘waiting lines’, then, are not just lines of human beings. They can also be aeroplanes trying to land at a busy airport, ships waiting to be unloaded, machine parts waiting to be assembled, cars waiting for traffic lights to change colour, calls arriving at a telephone switchboard, jobs waiting for computer processing, and anything else that requires work done on and for it. These queues are examples of costly, often critical delays. We observe that arriving units may form one line and be serviced through only one station (as in a doctor’s clinic), or they may form one line and be served through several stations (as in a hairdressing salon or a bank), or they may form a number of lines and be served through the same number of stations (as at supermarket check-out counters). Some queues form ‘in parallel’ and some ‘in series’; service times may be constant or variable. When queues form in parallel, the arriving customers create individual queues in front of each of several servers (as is common at supermarket checkouts). Customers may be served singly, as individuals, or in batches (such as groups of people travelling together who check in for a flight). When queues form in


Photograph: Erik Föster, www.peach.co.za

Solving N1 congestion A 5-year pilot project, costing about R23 million, is being initiated to ease congestion and improve road safety on the Ben Schoeman highway between Sandton and Pretoria, where some 48 accidents a year occur for every 10 km of road. About 70 closed-circuit television cameras will monitor traffic flow and help response and emergency teams to reach road accidents efficiently. Message signs along the route will update motorists on the traffic ahead. The South African National Roads Agency Limited (Sanral) is working with the Gauteng Department of Transport, and with Tshwane, Johannesburg, and Ekurhuleni local governments on this scheme. Sanral project engineer, Alex van Niekerk, expects it to increase throughput on the highway by 5% and to reduce ■ accidents by 20% ■ delays and associated costs by 30% ■ incident management response time by 55% ■ travel time by 5–10%. "Modelling results indicate that a 20-minute reduction in accident clearance on the Ben Schoeman could save 740 travel hours," says van Niekerk. Reported in Northcliff Melville Times (week ending 1 April 2005).

system can be changed and what the effects would be of various kinds of change – for example, they might calculate what would happen if an extra server were added at busy times and by how much the mean service time or waiting time would be reduced. Then, depending on the cost of change, they can decide if changes should be made at all.

Modelling the problem

Six basic characteristics describe a queuing situation reasonably well – distribution of arrivals, service time distributions, number of service channels, queuing discipline, system capacity1, and the number of service stages2. In a complex queuing network, the arrangement of channels and stages also needs to be specified. All these elements help to determine how efficiently a queue is working. But queuing problems cannot always be treated analytically and, even where they can, there’s no single decision-making procedure that applies to all situations. ‘First in, first out’ is one example of a queuing discipline. In various priority schemes, higher priority customers are served ahead of those with lower priority, and decisions need to be taken – for example, should the servicing of a current customer be interrupted or not when a higher priority customer arrives?

Dealing with queues efficiently means understanding and predicting what they might do. Queuing theory is a form of mathematical modelling that tries to do just that. It is concerned with the statistical description of the behaviour of queues. It tries, for example, to calculate the probability distribution of the number of customers in a queue for which it’s possible to find the mean and variance of queue length and the probability distribution of waiting time – either for a customer or for the distribution of a server’s busy periods. In the kind of operational research conducted to solve queuing problems, investigators measure the existing queuing system to assess its characteristics objectively and construct a model of it. Then they use that model to determine how the

Deciding what to do

In practice, dealing with waiting line problems often means making one or more decisions of the following kind (each represented here by a mathematical symbol): (1) the number of servers at a service facility (s); (2) the efficiency of servers (µ); (3) the number of service facilities (N ) . The first kind of decision is common – at checkout points in shops, for instance. An example of the second kind is the selection of the type of materials-handling equipment (servers) to transport certain types of load (customers). A decision as to the number of service facilities required occurs where toilets or storage areas need to be provided, for instance. Formulated in terms of a queuing model, the decision variables would be s, µ, N. Decisions have also to do with the appropriate level of service to be provided, and they involve two major considerations: (1) the cost of providing the service and (2) the amount of waiting for that service. The appropriate balance between service costs and delays can be decided only once the seriousness of each has been established. How much would it cost to reduce the queues in a supermarket just before a long weekend? What is the cost of traffic holdups on a motorway where hundreds of people are trying to get to work on time? ▲ ▲

series (or ‘in tandem’), the customers move through a succession of service channels to complete the operation. People catching a plane experience a series of queues, for example, when they proceed through check-in, then security checkpoints, passport control, and final boarding. Many manufacturing and industrial productionline processes also use this type of queuing system.

1 System capacity refers to the limit on the number of waiting spaces. 2 Number of service stages refers to the number of queues through which a customer must proceed.

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Calculating costs and benefits Once the cost of waiting is known, the next step is to determine what level of service improvement will most reduce the total cost of the service. This means calculating, for each option, the expected total cost (ETC ) – i.e. the expected service cost (ESC) plus the expected waiting cost (EWC). The aim is to minimize ETC = ESC + EWC. To illustrate, consider a single service system.

Case study A firm has several machines and wants to install its own service facility for repairing them. The average breakdown rate () of the machines is 3 per day. The repair time has an exponential distribution (the repair rate is constant). The loss incurred when a machine is out of action is R400 per day. The firm can choose to install one of two repair facilities. Item Cost of installation Labour cost per year Number of machines it can repair each day ( ) Lifespan

Facility A R 200 000 R 50 000 4 4 years

Facility B R 400 000 R 80 000 5 4 years

Question Which facility should be installed? Calculation Total annual cost  1/4 (cost investment expenditure)  (annual labour cost)  (annual cost of lost revenue due to inoperative machines) Facility A Annual capital cost  1/4 (R200 000)  R50 000 Annual labour cost  R50 000 Expected number of machines for repair in the system

  3  3 per day  43

The daily cost of lost time  3  R400  R1 200 Annual cost of lost machine time  365  R1 200  R438 000 Total annual cost of Facility A  R50 000  R50 000  R438 000  R538 000 Facility B Annual capital cost  1/4 (R400 000)  R100 000 Annual labour cost  R80 000 Expected number of machines for repair in the system

  3  1.5 per day  53

The daily cost of lost time  1.5  R400  R600 Annual cost of lost machine time  365  R600  R219 000 Total annual cost of Facility B  R100 000  R80 000  R219 000  R399 000

Answer Facility B is the preferred option.

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The cost of waiting time can be considered proportional to the time of waiting. Estimating this cost is not always easy and depends on the situation. When customers are external to the organization, for instance, the cost of waiting may be seen as the profit lost due to customers’ dissatisfaction – tired of queuing in one store, they might choose to shop elsewhere. It is easier to estimate waiting costs when customers are internal to the organization: when the entities in question are machines or employees, for example, the cost associated with idleness is readily calculated. Once the cost of waiting has been assessed, the next step is to calculate the cost of reducing that waiting time and, finally – taking all the circumstances into account – to decide whether or not a change is worth making. ■ Professor V.S.S. Yadavalli, Professor Kris Adendorff, and Gert Erasmus are in the Department of Industrial & Systems Engineering, University of Pretoria and Professor V. Yegna Narayanan is at the M.N.M. Jain Engineering College, Chennai, India. For more, consult J.A. Buzacott and J. George Shantikumar, Stochastic Models of Manufacturing Systems (New Jersey: Prentice Hall, 1993); D.G. Carmichael, Engineering Queues in Construction and Mining (Chichester: Ellis Horwood, 1987) and J.H. Dshalalow (ed.), Advances in Queuing Theory, Methods and Open Problems (Boca Raton, Florida: CRC Press, 1997).

Water (and life?) on Mars

For over a year, NASA’s twin rovers, Spirit and Opportunity, have explored Mars for signs of water and life. The evidence they found of past water was, according to the journal Science, the top scientific “Breakthrough of the Year”. Spirit landed on 3 January 2004, in Gusev crater, followed by Opportunity three weeks later, on the opposite side of the planet on Meridiani Planum. The landings were complicated. Each spacecraft had to enter the atmosphere the right way, deploy its parachute, turn on retrorockets, and inflate airbags just before touchdown – the loss of the European Beagle 2 probe days earlier showed how difficult this could be. Designed to last for 90 days on Mars, the rovers continue their work with no indications of stopping. Today the Martian surface is dry, but evidence that water once flowed there offers the possibility of life. Furthermore, three independent teams (one using instruments on the Mars Express orbiter and two using ground-based telescopes) have detected methane in the Martian atmosphere. Nearly all Earth’s methane comes from living things such as rotting plants, so signs of it on the red planet could mean living microbes there too. The methane (possibly exhaled by bacteria) occurs in the same spots as water vapour, so these are potential habitats for life. But we need more tests to determine the origins of the gas and

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to eliminate the possibility that it came from volcanic eruptions, for instance, or from the impact of a comet. If life created the methane, say scientists, the ratio of carbon-12 to carbon-13 isotopes should prove it. Another approach is to look for seasonal variations – non-biological sources might depend on seasonal temperature changes whereas organisms living deep below the inhospitable surface would be shielded from them. Till this mission, Martian bedrock had never been observed up close: now it is seen repeatedly at both landing sites. Having for the first six months viewed only volcanic rock and wind-blown dust, Spirit’s cameras reached an area where water seemed to have affected every rock. The layered deposits on these rocks, scientists believe, could have formed from volcanic dust that either mixed with water vapour or became thinly coated with water. Supporting the case for water were the high concentrations of sulphur and chlorine (which are soluble in water). The amounts of each mineral detected has suggested that they were leached out and repeatedly redeposited by water that may have been there only briefly and in small amounts. Spectral measurements by the orbiting Mars Global Surveyor showed an unusual concentration of haematite (a form of iron oxide) at Meridiani Planum. On Earth, haematite is normally formed in water, but another type forms at the high

temperatures found in volcanoes. The form of haematite that Opportunity encountered was in tiny spheres, like beads, littering the plains as far as the camera could see. Nicknamed ‘blueberries’, they showed clear signs of having been built up layer by layer within sediments, like the pearls in our oceans. Soon, spectroscopic and morphological results ruled out non-watery explanations. Meridiani seems to have the characteristic chemistry of lakes repeatedly appearing and then drying out, leaving a flat expanse of salty residue. This recurring cycle built up a series of crusty, crumbly layers. The minerals in the rock show that the water was also very acidic – similar to old mines on Earth that are contaminated with sulphur and acid. The flat plain of Meridiani also has characteristic patterns looking like waves in shallow water, unlike the shapes formed by wind. Perhaps much of the Martian northern hemisphere was once a vast ocean and the Planum a continental shelf, alternating between dry and wet phases? Water is needed for life as we know it and, on Earth, even the most inhospitable places can harbour both. Now that we know of long-lasting bodies of water on Mars, the search is on for life. Stay tuned. From a report in New Scientist (15 January 2005). For updates visit www.nasa.gov


The problem with a healthy diet is that nobody seems to want to follow it, says Alex Walker. We know what kind of lifestyle is good for us, so why don’t we behave accordingly? Photograph: Erik Föster, www.peach.co.za

Prevention pays There seems to be no doubt that healthy living is good for you. Remarkable results emerged in 2004, in a follow-up study after 10 years on a series of elderly white men and women aged 70–90 years. They had adhered to a Mediterranean type of diet, were nonsmokers or had stopped smoking more than 15 years earlier, were physically active, and used alcohol moderately. They had mean daily consumptions of 284 g vegetables, 214 g fruit, and 245 g cereal foods (such as oats, rye, wheat, rice, and maize). When compared with a control group, the combination of practices described was associated with a mortality rate of about one-third of those following none or only one of the protective health behaviours. Emphasizing the many health advantages of the recommended increased consumptions of fruit and vegetables, a 2000 report on the US Health Professionals Follow-up Study found that men with a “prudent” dietary pattern, characterized by high intakes of fruit and vegetables, legumes (such as beans, peas, and lentils), whole grains, fish, and poultry, had only half the risk of coronary heart disease as men with a low intake of these foods.

Bad habits die hard In general, there is great reluctance to change everyday diets and habits to improve health, particularly among people with adequate incomes. A survey report of 2000 on older men in Caerphilly, UK, found that only 4.3% of the men questioned followed a recommended target of eating five portions of fruit and vegetables a day, while 33% consumed one or fewer portions of fruit and vegetables a day (a portion is about 75 g).

Start young The South African Nutrition Expert Panel examined diet and exercise taken by children aged 8–13 years around the country. It reported that: ■ fast foods often replace cooked meals ■ children left alone eat snacks, watch TV, play computer games, and don’t exercise enough ■ breakfast is often skipped ■ school tuck shops give unhealthy choices (pies, chips, sweets, fizzy drinks, bread, fat-laden cakes, vetkoeks). According to the UCT/MRC Research Unit for Exercise Science and Sports Medicine, 20% of South African children aged 6–12 years old are overweight or obese. For more on the research, visit www.nutritionexperts.org.za or call Carla of Sabio Communications at (011) 476 8270. For body image issues, visit www.mindoverfatter.co.za (Reported in Northcliff Melville Times, week ending 22 April 2005.)

Similar bad habits were reported two years later in the results of a survey of a group of young medical students who, with their knowledge about nutrition, should have known better. The research established that “only a quarter ate at least five daily servings of fruit and vegetables, and only 2% had a diet which included at least 20 g fibre, and a mere 18 % exercised during the period for 5 or more days each week.” Despite repeated urgings for people to eat more fruit and vegetables, a major study (published in 2004) on trends in fruit and vegetable consumption among adults in the USA indicated that their habits had changed little from 1994 to 2000 – indeed, little since 1976. Public inertia notwithstanding, the US National Cancer Institute has once again strongly recommended that, for major benefit to

health, 5–9 servings of fruit and vegetables should be eaten daily.

Time to change All the facts unquestionably point to the major benefits of changing to healthier lifestyles, but there seems to be universal lack of interest in seeking seriously to lengthen years of healthy life expectancy. Referring mainly to decreases in physical activity and increasing obesity, the editor of the medical journal, The Lancet, last year deprecated “the catastrophic failures of public health.” A serious new focus of attention for individuals and nations alike is to find ways to persuade people to do what is necessary to lead long and healthy lives – and to change whatever habits they have that get in the way. ■ Dr A.R.P. Walker is with the National Health Laboratory Service in Johannesburg. He is 92 years old and has worked in the field of nutrition since 1946 For more on the surveys quoted in this article, consult K.T.S. Knoops et al., “Mediterranean diet life-style factors, and 10 years mortality in elderly European men and women: the HALE Project”, Journal of the American Medical Association, vol. 292 (2004), pp.1433–1439; J.J. Strain et al., “Frequency of fruit and vegetables consumption and blood antioxidants in the Caerphilly cohort of older men”, European Journal of Clinical Nutrition, vol. 54 (2000), pp.828–833; D. Payne, “Medical students learn to cater for health appetite”, Lancet, vol. 359 (2002), p.1220; F.B. Hu et al., “Prospective study of major dietary patterns and risk of coronary heart disease in men”, American Journal of Clinical Nutrition, vol. 72 (2000), pp.912–921; M.K. Serdula et al., “Trends in fruit and vegetable consumption among adults in the United States: behavioral risk factor surveillance system, 1990–2000”, American Journal of Public Health, vol. 94 (2004), pp.1014–1018; and A.K. Kant, “Consumption of energydense, nutrient-poor foods by adult Americans. The Third National Health and Nutrition Examination Survey, 1988–1994”, American Journal of Clinical Nutrition, vol. 72 (2000), pp.929–936. For further details, read S. Gottlieb, “Men should eat nine servings of fruit and vegetables daily”, British Medical Journal, vol. 326 (2003), p.1003 and G. Critser, “Fat Land: How Americans became the fattest people in the world”, British Medical Journal, vol. 326 (2003), p.229.

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Spiders are not only beautiful but also useful, explains Ansie Dippenaar-Schoeman, and theyâ&#x20AC;&#x2122;re fascinating in many unexpected ways.

Wonderful spiders

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See below for title-page captions (pp.24–25). Main photograph (p.25): Hammock web spiders (Linyphiidae) make permanent webs in vegetation. This one, built in a tree, is clearly visible in early morning light. Photograph: Carina Cilliers 1 Ant spiders (Corinnidae, Apochinomma) are free-living ground wanderers that mimic ants to escape predation. This one is feeding on an insect. Photograph: Les Oates 2 Flower crab spiders (Thomisidae, Thomisus daradioides) are free-living spiders that live on flowers. The males are much smaller than the females. Here, a female is sitting in ambush in a flower head with a small male on her abdomen, waiting to mate. Photograph: Les Oates

3 This female pink flower crab spider (Thomisidae, Thomisus citrinellus) is waiting in ambush on a flower to catch visiting flying insects. These spiders can change colour from white or yellow to pink. Photograph: Les Oates 4 This green hairy field spider (Araneidae, Araneus apricus) is sitting on a prickly pear. These nocturnal orbweb dwellers build their orb webs at night to catch prey and remove it early next morning. Photograph: Boeta Fourie 5 Green flower crab spider (Thomisidae, Synema) moving around on vegetation in search of food. Photograph: Norman Larsen

6 A funnel web spider (Agelenidae, Agelena) on a funnel web made close to the soil surface in a cave. The funnel-shaped retreat of this permanent web dweller is visible in the background. Photograph: Mike Buchanan 7 This ground sac spider (Miturgidae), a nocturnal wanderer, is running on a log: its silk guide line is clearly visible in the background. Photograph: Norman Larsen 8 A female spotted hairy field spider (Araneidae, Pararaneus cyrtoscapus) in her orb web. Photograph: Les Oates 9 This brightly coloured ladybird crab spider (Thomisidae, Camaricus nigrotesselatus) is free-living and found on vegetation, usually on a layer of grass or young green plants. Photograph: Jim Cambray

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piders are special

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Spiders (Araneae) are common in and around houses, in gardens, and in fields, and they are among the most abundant forms of wildlife you’ll see if you go on a walking trail. This is not surprising, as they rank seventh among terrestrial animals in global diversity. Spiders are unique mainly because of their ability to produce silk, to produce venom, and to adapt successfully to their environment. These characteristics help them to survive and make them excellent predators. They are important in terrestrial ecosystems as they feed almost exclusively on insects and mites and help to keep pest populations under control. About 37 400 species have so far been described globally, but we expect this number to rise to about 170 000 as new species are identified. South Africa has a rich fauna and there are 67 families represented by about 2 500 species in the region. But we have few taxonomists and taxonomic information on most families from South Africa is still rudimentary. One of the greatest threats posed to our conservation of arachnids overall is the fact that we still have insufficient baseline data, so much remains to be done. Although spiders are absent from most Red Data lists, they are nevertheless seriously The class Arachnida Spiders belong to the class Arachnida, which includes all eight-legged animals. They are second only to insects in abundance and diversity. South Africa has a rich Arachnida fauna and 9 of the 12 extant orders occur here, namely: ■ false-scorpions (Pseudoscorpiones) represented by about 135 spp. (species) ■ harvestmen (Opiliones) with 179 spp. ■ micro whip-scorpions (Palpigradi) with 2 spp. ■ mites and ticks (Acari) with more than 2 350 spp. ■ schizomids (Schizomida) a single sp. ■ scorpions (Scorpiones) with 95 spp. ■ sunspiders (Solifugae) with 150 spp. ■ whip-scorpions (Amblypygi) with 3 spp. ■ and spiders (Araneae) with about 2 000 spp. There are 93 500 known species of arachnids, 9 165 genera, and 570 families worldwide. South Africa has about 5 000 known species, which represents 8% of their global diversity. Currently, 75% of the arachnids found here are endemic (that is, they are found nowhere else).

Some spider facts ■ Depending on the species, spiders can lay up to 9 000 eggs during their lifetime ■ They first moult in the egg sac and when the spiderlings emerge they closely resemble adults ■ Young spiders have 6–9 moults before they become adults and after their last moult they are ready to mate ■ Most spiders live between 9 and 18 months, but baboon spiders can live up to 25 years ■ Spiders can lower their metabolism, which helps them to survive for long periods without food or water and to adapt to adverse or extreme climatic conditions ■ To survive, they use defence mechanisms, such as playing dead and putting on aggressive displays ■ Masters of camouflage, they can blend into their surroundings to escape predators using colour, shape, and behaviour as disguises ■ With the exception of one family, all spiders produce venom to kill their prey, but only a few of them produce venom that is known to have medical importance for humans.

threatened by human activities. Those of the suborder Mygalomorphae and especially the larger baboon spiders of the family Theraphosidae are in demand as pets and, because of this, they are classified as Commercially Threatened. Only three genera of South African spiders are protected.

Spin doctors par excellence The most outstanding characteristic of spiders is their ability to secrete silk for use in activities unheard of in other animals. Their silk ■ enables spiders to move around freely, and makes them one of the few animals without wings that can ‘fly’. (The spider produces a thread, which can be suspended in an air current to carry it away in the direction the wind is blowing in a process called ‘ballooning’.) ■ guides them, anchors their webs, and prevents them from falling (mooring, or support, threads anchor the web to a fixed point; pilot threads guide a spider when it moves about on the web; signal, or trip, threads betray the presence of prey or a predator in the web; and catch threads, which are often strong and sticky, help to ensnare the prey) ■ provides material for constructing shelters that range from silk retreats to silk-lined burrows with trapdoors


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10 Nursery web spiders (Pisauridae, Euphrosthenops australis) live permanently in funnel-like webs.

Spider silk The Guinness Book of Animal Records 1995 gives spider silk as the strongest of all natural and manmade fibres, stronger even than steel. The dragline of a European garden spider (Araneus diadematus), for example, can support a weight of 0.5 g without snapping, whereas a steel strand of similar thickness snaps under the strain of just 0.25 g. Spider silk is one of the great wonders of the animal kingdom. It is tough and stronger and more flexible than any substance known. It has been suggested that a pencil-thick strand of silk could stop a Boeing 747 in flight.

Photograph: Boeta Fourie

11 Green tree crab spiders (Thomisidae, Oxytate ribes) are freeliving and normally found on trees. They are common in orchards, where they prey on pests. This male is camouflaged on the tip of a leaf. 17 18

Properties of silk Strong – by weight, it is five times the strength of steel Light – lighter than cotton Elastic – it can stretch 2–4 times its length Thin – it is finer than hair and does not break, even at temperatures as low as 40ºC Resistant – it is waterproof; and resistant to bacteria and fungi. Research into silk production includes ■ cloning a specific gene and inserting it into bacteria to manufacture the desired protein ■ injecting silk genes into full-size milk-producing animals (for example, the African goat) and then extracting pure silk from the milk to form a product called Biosteel. Bio-engineered materials of this kind are environmentally friendly, as they are renewable and biodegradable and they use organic processes rather than minerals. Spider-silk fibres give high strength and elasticity and they improve the strength of textiles. They can be used in making a range of artifacts that need to be light and strong, such as: artificial tendons or ligaments, lighter bullet-proof vests, seat belts, rust-free bumpers, bridge suspension cables, and parachute chords. ■ helps to protect eggs from harsh weather and

predators ■ is used to wrap prey ■ assists in mating (when the male deposits sperm

on a sperm web before mating, for instance) ■ helps them to create intricate and ingenious

Hunters Spiders can be divided into two main groups: web-builders and free-living wandering spiders. Specialized spider predators and the adaptation of some insects to avoid being captured in webs meant that many spider species abandoned webs and became free-living wandering spiders, that is, hunters that rely on the strength of their legs and venom to catch and kill their prey. We classify them, according to their preferred habitat, as ground dwellers or plant dwellers.

Smart predators Spiders succeed as predators because of the efficient ways in which they exploit insect populations and because they are specially adapted for a predatory way of life. ■ A distensible abdomen enables them to consume large amounts of food in a relatively short time, and their predation rate can greatly increase during short periods when plenty of food is available. ▲ ▲

traps for catching prey. The use of webs for capturing prey probably developed long after spiders came into existence, and it took more than 200 million years for the first orb web to appear (during the Jurassic period). The wide range of web types – including funnel webs, gumfoot webs, orb webs, retreat webs, sheet webs, signal webs, and space webs –

suggests that this strategy is very successful. Spider webs are highly specialized structures. They are normally built over open spaces and vary in diameter from a few centimetres to several metres.

Photograph: Boeta Fourie

12 Daddy-long-legs spiders (Pholcidae, Smeringopus natalensis) live in space webs made in dark corners. This female is hanging in her web. The eggs carried in a sac in her mouth have hatched and numerous spiderlings can be seen around the remnants of the egg sac. Photograph: Les Oates 13 Baboon spiders live in burrows. This female Soutpansberg starbust baboon spider (Theraphosidae, Augacephalus junodi) is showing her fangs in an aggressive display. Photograph: I. Roesch 14 This female ladybird spider (Araneidae, Paraplectana thorntoni) is resting on bark. Photograph: Les Oates 15 A nocturnal, web-dwelling hedgehog spider (Araneidae, Pycnacantha tribulus) feeding on a moth. It makes a reduced orb web and, while hanging on a small trapezium web, uses pheromones to attract the moth and then grabs it out of the air with outstretched legs. Photograph: Les Oates 16 The agile termite-eating spider (Ammoxenidae, Ammoxenus amphalodes) lives on the ground and, as the name suggests, is a specialist feeder of harvester termites. It is active around harvester termite nests: this one is busy diving head first into the sand. These spiders live just below the soil surface. Photograph: Les Oates 17 This is a wandering ground dweller and a specialist termite-eating spider (Ammoxenidae, Ammoxenus amphalodes). Here it is preying on a harvester termite. It kills the termite and pulls it below the soil surface before starting to feed. Photograph: M. de Jager

18 This colourful, hairy flower crab spider (Thomisidae, Thomisus granulatus) is waiting for prey. Photograph: Boeta Fourie

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■ Their high resistance to starvation (because

19 This female Transvaal golden baboon spider (Theraphosidae, Idiothele nigrovulva) defends the entrance to her burrow.

they’re able to lower their metabolic rate) enables them to survive and maintain normal reproduction during periods when not much prey is available. ■ Most spiders are polyphagous (that is, they have insatiable appetites) and feed on a variety of prey, but some are specialists and prey, for example, on termites or ants only. ■ They eat their prey at all stages of development – including eggs and larvae as well as adults – so they can inhibit the initial build-up of prey populations.

Helpful pest controllers Spiders are common in agro-ecosystems (that is, on cultivated land). Little attention has been given so far to their possible use in pest control, but there is increasing interest worldwide and in South Africa in spiders as natural control agents of insects and mites where crops are grown. High numbers of spiders occur on crops. In year-long surveys, for example, 90 species have been recorded in avocado tree orchards, 80 species in macadamia, 134 in citrus, 127 in cotton, and 87 in pistachio orchards in South Africa. They are among the very first arthropods to colonize newly planted crops, and their numbers increase with plant density and prey numbers. In some crops they represent 70% or more of the predatory complex. They use different hunting strategies and foraging modes to obtain prey. Some species, like the termite eaters (Ammoxenidae, Ammoxenus), are specialist feeders preying only on termites. Spiders are also important indicator species for environmental risk analyses in determining the extent of ‘collateral damage’ that human activity can cause to the environment. Current surveys are trying to determine the extent to which Bt cotton and Bt maize (see p. 34) affects spider populations, for example, and research is also exploring the extent to which sprays and other means of controlling pests, such as quelea and tsetse fly, affect spiders too. The use of spiders as biological control agents requires their conservation and possible augmentation in agro-ecosystems. Augmentation is difficult because rearing spiders is as yet prohibitively time-consuming and expensive, but sustainable use of spiders can be

Photograph: Les Oates

20 The web of a grass orb web spider (Araneidae, Kilima decens) in the early morning, with dew on the silk threads. Photograph: Les Oates 21 A large hairy field spider (Araneidae, Neoscona hirta) in its orb web. Photograph: Boeta Fourie

accomplished where farming practices are spider-friendly.

Spider-educare programme The ARC-Plant Protection Research Institute is involved in educational activities to raise awareness of spiders as a gardener and farmer’s best friend and to persuade children not to kill but to appreciate them – and arachnids in general – for their wonderfully diverse and interesting life styles. ■ For information about our lectures, road shows, wall posters, CDs, and books, visit www.arc-ppri.agric.za For contact with people in your area who are knowledgeable about spiders, phone (012) 356 9824. Dr A.S. Dippenaar-Schoeman is a Specialist Scientist at the ARC-Plant Protection Research Institute, Private Bag X134, Queenswood 0121 and she is also attached to the Department of Zoology and Entomology, University of Pretoria. For 38 years she has been researching spiders and is involved in projects ranging

Spider research in South Africa In 1997, the South African National Survey of Arachnida (SANSA) was launched at the Plant Protection Research Institute, one of the institutes of the Agricultural Research Council (ARC), in accordance with the country’s obligations to the Convention on Biological Diversity. It aims to make an inventory of the arachnid fauna of South Africa that will provide essential information for the conservation and sustainable use of our arachnid fauna, as our knowledge of the larger arachnid orders such as the mites and spiders is still sketchy in terms of their taxonomy, ecology, and distribution. This umbrella project is conducted nationwide in collaboration with researchers and institutions around the country. As part of SANSA, projects are under way to determine the diversity of the spider fauna of South Africa. They include inventories of the spider fauna of the different floral biomes, conserved area, agro-ecosystems, provinces, and the urban environment. For more on spiderstoofbiodiversity South Africa, assesments. consult the following books. A.S. Dippenaar-Schoeman & R. Jocqué, African from taxonomy Spiders, an Identification Manual, Handbook 9 (Pretoria: ARC-Plant Protection Research Institute, Biosystematics Division, 1997); A.S. Dippenaar-Schoeman, Baboon and Trapdoor Spiders of Southern Africa, an identification manual, Handbook 13 (Pretoria: ARC-Plant Protection Research Institute, 2002); A.S. Dippenaar-Schoeman, The Spider Guide of Southern Africa (Pretoria: ARC-Plant Protection Research Institute, 2002; CD-ROM version 2001).

Quest 1(4) 2 0 0 5 29


Spider webs are normally too fragile to be fossilized and they are constructed in the wrong places. Yet there are spider webs in the fossil record, writes Martin Pickford, some of them tens of millions of years old. How can such ephemeral structures become fossils and what can such fossils tell us about the past?

Above left: A present-day male Seothyra. Photograph: Les Oates (Picture reproduced courtesy of the ARC-Plant Protection Research Institute)

Above right: Half of a fossilized roof web cemented onto a burrow-shaped nodule of indurated dune sand was found at Rooilepel, near Oranjemund. Wind-blown sand had probably destroyed the missing half of the web. Picture: Courtesy of Martin Pickford

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ver the last century, palaeontologists have found many fragments of spider webs in amber, which is fossilized tree gum. The webs (or small fragments of them) get incorporated into exuding tree gum, which flows over them and preserves them so perfectly that arachnologists (people who study spiders) can often tell what family of spiders made the web and even what part of the web is preserved â&#x20AC;&#x201C; for example, signal threads or web fibres with sticky globules of silk for trapping insects. Amber containing fossil spider web is known from Europe, the Middle East, and the Caribbean, the oldest specimens being from the Cretaceous period, some 100 million years old. Until recently, amber was the only known source of information about fossil spider webs, and it was generally thought to be the only means for preserving such fragile structures. But discoveries in the Namib Desert have radically changed our thinking and opened up a new field of research.

A mystery solved The Namibia Palaeontology Expedition started surveying the fossil sand dunes (aeolianites) of the Namib Desert in 1992 and discovered many fossil bird eggs and reptile and mammal bones and teeth, as well as a bewildering variety of trace fossils made by small animals, such as beetles and

rodents, that burrowed through the sand when it was loose. The expedition also found fossilized termite mounds, petrified beetle cocoons, and even some mineralised wood lice, preserved in calcite (CaCO3). But most extraordinary of all was finding small white dome-shaped structures with lobed margins about 2 cm across, similar in shape to clover leaves. Each of these structures is preserved as a layer of calcite about 2 mm thick cemented onto a nodule of hardened sand*. For several years we didnâ&#x20AC;&#x2122;t know what these structures were, till I observed some peculiar traces in the sand near the Tsondab River in the Namib-Naukluft Park. These looked superfically like antelope spoor but did not occur in trails; they were scattered randomly over the surface of the sand. Excavation of one of them revealed a mat of thick spider web with a vertical tubeshaped burrow beneath, and the literature soon revealed that it was made by the buck spoor spider (Seothyra). The similarity of these Seothyra roof mats and the calcite domes was immediately apparent.

How a web becomes fossilized The structure of the Seothyra tube and roof web is extremely fragile. A strong wind, for example, can easily destroy it by blowing away the sand, or a passing gemsbok or hyena could step on it and ruin it. After hatching, baby Seothyra eat

* The expedition collected several of these structures near Sossus Vlei, Namibia, and at Rooilepel, not far from Oranjemund in the Sperrgebiet. Specimens found in situ revealed that the domes were originally orientated with the convex part upwards and the nodular part downwards. A specimen from Rooilepel preserved part of a burrow-shaped nodule beneath the calcite layer.


their mother, and they consume the roof web as well because it is a rich source of protein. So physical destruction is probably the fate of more than 99.9% of the webs ever built. Now and then, one will be buried by windblown sand and protected from such damage. Even then, its chances of survival are infinitesimally small – the web can rot and fossorial insects, of which there are many in the Namib, can eat it or damage it by their burrowing activities. Very occasionally, however, the sand surrounding the web becomes moist (perhaps after rain, or due to fog precipitation or to a rise in groundwater level), which improves its chances of being preserved. The moisture can dissolve calcium carbonate from surrounding sand, which can then diffuse into the spider web. The pore spaces in the surrounding sand are too large for them to act as diffusion traps, but the pore spaces in spider webs are of suitable dimensions for such chemical processes to occur. With sufficient diffusion of molecules of calcium carbonate into the web structure, the entire web can be replaced by calcite – the web is fossilized. Millions of years later, wind may erode the surrounding sand to uncover such fossils, exposing them to physical damage. But once in a while a passing palaeontologist may notice a small white gleaming dome-shaped structure with lobed margins, may bend down to pick it up, and may even wonder what it is before throwing it away. Or he may keep it, and embark on a lengthy search to interpret how it formed, how old it is, and what it means.

What the fossils reveal

Photograph: Martin Pickford

How the Seothyra catches its prey Seothyra is a small spider that burrows into loose soil and sand, where it excavates a short vertical tube that it lines with strands of web to prevent the sides from collapsing inwards. It covers the top of the burrow with a thick ‘mat’ or ‘roof web’ about twice the width of the tube and camouflages its upper surface with sand. Wind-blown sand also covers the structure until it becomes invisible from above. The roof web is built with marginal lobes (normally four) that are flexible enough for the spider to lift up without dislodging the entire web. The spider then spins a mass of sticky web, called a cribellar tangle, almost like a miniature ball of tangled wool, which it leaves near the edge of each of the lobes. These cribellar tangles are connected to signal threads which lead to the centre of the roof web, and from there go vertically downwards into the tube, at the bottom of which waits the spider, away from the heat of the desert surface. Any unwary insect, such as an ant or a small beetle, that touches the Seothyra burrow and roof web cribellar tangle is temporarily stuck prey to it and, as it wriggles to free itself, sand mat spider it vibrates the signal thread alerting the spider at the bottom of the pit burrow that its next meal is trying to sticky silk get away. By analysing the vibrations chamber collar-door in the signal threads, the spider can tell which of the lobes to lift so as to capture its prey. Each time it lifts a lobe, it disturbs the sand that covers it, and when it lowers the lobe back silk-lined burrow signal thread into position it leaves a small crescentic depression in the surface of the sand. With repeated lifting and lowering of each lobe, it produces the characteristic ‘buck prey remains spoor’ pattern in the sand.

the region for the past 17 million years. They also provide the only known evidence of the existence of these spiders in the fossil record: no body fossils of Seothyra have ever been found. Other trace fossils that occur in dizzying quantities and innumerable varieties in the Namib aeolianites will yield precious information about the evolution of the Namib fauna and flora and the climatic conditions at various stages in the desert’s history. Fossilized

▲ ▲

Seothyra currently occurs widely in southern Africa in areas where there is loose sand or gravelly soil that is dry most of the year. In the Namib Desert, the spiders survive at the thermal limit. Exposed to the heat of the desert day for a few minutes they die, but waiting safely in the bottom of their burrows, where the temperature is much lower than at the surface, they are safe. If a passing ant gets caught in the trap on the surface, the spider dashes up its tunnel, lifts the appropriate marginal lobe, captures its prey, carries it down to the bottom of its tunnel, and eats it at leisure. The discovery at Rooilepel of 16million-year-old fossil webs that look extremely similar to those of extant Seothyra reveals that buck spoor spiders quickly adapted to the sandy desert conditions that became established in the Namib at that time. Many plants and animals were affected by the climatic changes from savanna to desert. Savanna species went extinct locally or they adapted, evolving into new forms. The burrowing spiders, because of their subterranean behaviour, were partially buffered from the full harshness of the desert environment and had a head start on many inhabitants of the region. The fossilized Seothyra roof webs preserved in the fossil dunes of the Namib elegantly attest to the rapid adaptation of this family of spiders to the extreme conditions in

Surface view of two buck spoor spider burrow complexes. The crescent-shaped depressions in the sand, which give the structure its name, occur at the edges of the flexible lobes in the roof mat. They are lifted by the spider to catch a passing insect and lowered when it carries the prey down into its burrow, located beneath the roof web.

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Climate change in the Namib Before the Middle Miocene period (some 16–17 million years ago): the Namib was a savanna area, with grassland, trees, and various vertebrates (e.g. primitive antelopes, ostriches, crocodiles, and dassies). At the end of the Early Miocene: the Antarctic Ice Cap expanded to continental scale, causing global climatic changes. The cold climatic belts increased in area, and the subtropical and tropical ones were squeezed northwards towards the equator. The Southern Namib changed from savanna to steppe, and winter rainfall replaced the summer rainfall of the Early Miocene. From steppe to hyper-arid desert: The new configuration of the world’s climatic belts led to the formation of the South Atlantic anticyclone as we know it today; the dune bedding in the indurated sands of the Namib show consistent southerly wind directions from 17 million years ago to today and, in that time, vast volumes of glacial melt water have been shed into the oceans surrounding the Antarctic continent. Being fresh and cold (therefore denser than seawater), melt water sinks to the ocean depths and flows away from the continent. The rotation of the globe ensures that the cold bottom water drifts northeastwards, where it eventually encounters the continental shelves on the west side of continents (South America, southwest Africa, and western Australia). Here the water is forced upwards by a combination of two factors: the upward slope of the continental shelf and the offshore winds related to the South Atlantic anticyclone that blow surface waters away from the shore towards the open ocean. Water wells upwards from the depths to fill the place left by the departing surface water: these upwelling cells of cold water intensify the arid conditions along the southwestern coast of Africa, turning the Namib from semi-arid steppe into hyper-arid desert.

Picture: Courtesy of Martin Pickford

Two views of a Late Miocene Seothyra fossilized roof web. The dome-shaped structure and its lobed margin are typical of this kind of fossil, which is generally about 2 cm in diameter.

termite nests and hives abound in the fossil dunes and reveal that the climate of the southern Namib has fluctuated between summer and winter rainfall several times in the last 17 million years. Some trace fossils (called ichnofossils by palaeontologists) are so well preserved that we can identify the organisms that made them. This is particularly so for fossilized ‘bioconstructions’, a class of ichnofossils manufactured from body contents of the makers rather than from sediment. Most trace fossils, such as footprints and back-filled burrows, result from the passage of organisms over or through sediment and their makers are therefore difficult to identify. Being constructed of organic matter, bioconstructions are more readily attributed to their makers. Fossilized bioconstructions, such as the petrified hives of harvester termites (Hodotermes), are large and spectacular.

Till now, however, because of their fragility, the most surprising ichnofossils to come out of the Namib Desert are the roof webs of Seothyra. Their preservation gives scientists intriguing glimpses into the Miocene palaeoecology of burrowing spiders in desert environments and provides a precious piece of the puzzle which is the history of the Namib Desert. ■ Dr Martin Pickford is Maître de Conférences in the Chaire de Paléoanthropologie et de Préhistoire, Collège de France, and is a member of the Département Histoire de la Terre, UMR 5143 du CNRS, Case postale 38, 57 rue Cuvier, 75005, Paris. He has conducted palaeontological research in many African countries. His main interests concern the evolution of hominids, especially the stages before the human lineage was established some six million years ago. He carries out these studies in the context of the palaeoenvironments and palaeoclimates in which the evolutionary processes occurred. Hence the interest in Seothyra and other sources of information that can indicate past climatic conditions in the continent.

News Q Red’s a winner

A drink a day (but no more)

The colour red in certain animal, fish, and bird species is a sexually selected sign of male quality, and attaching artificial red stimuli experimentally can increase the male’s dominance. Now scientists show that the colour red can improve human performance across a range of competitive sports. In the 2004 Olympic Games, contestants in four combat sports (boxing, tae kwon do, Greco-Roman wrestling, and freestyle wrestling) were randomly assigned red or blue outfits (or body protectors). For all four competitions, contestants wearing red consistently won more fights. Across rounds in each competition, 16 of 21 rounds had more red than blue winners, with only four rounds having more blue winners; across weight classes in each sport, 19 of 29 classes had more red winners, with only six having more blue winners. The statistically significant advantage apparently extends to team sports. In the Euro 2004 international soccer tournament, teams wore shirts of different colours in different matches. The results of five teams were analysed, and each did better when they wore predominantly red shirts and played against opponents in colours other than blue (four played their other matches in white, one in blue). Given differences of skill and strength among contestants, the advantage of wearing the colour red is greatest where the contestants are evenly matched. But maybe it’s worth regulating the colour of sportswear, to ensure level playing fields in sport? Reported in Nature (19 May 2005).

A single drink a day can protect older women against mental decline, say two new studies. US researchers followed alcohol consumption among more than 11 000 women enrolled in one of the largest investigations into the risk factors for major chronic illnesses in women. Over six years, starting in 1995, they assessed the mental status of women 70 and older, using tests of memory, verbal fluency, and general mental skills. Women who consumed one drink a day (up to 15 grams of alcohol) had significantly better test results, scoring about a year and a half younger than the nondrinkers or than those who drank 15–30 grams a day. Another study, using different tests of mental ability, reported similar results in a group of 4 460 women. Such benefits could be connected to the significantly lower rates of cardiovascular disease among moderate drinkers. Also, alcohol appears to raise levels of HDL (so-called ‘good’) cholesterol and to reduce levels of certain blood clotting agents, perhaps helping to prevent heart attacks and the small, subclinical strokes that cause vascular damage in the brain and lead to mental deterioration. More studies are needed, however, before nondrinkers should be encouraged to start drinking alcohol, say doctors, and everyone without fail needs to guard against alcohol abuse. Reported in The New York Times (1 February 2005).

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Q Viewpoint

Backing the GMO horse: what are the odds The race is on to provide risk-free food for growing human populations, particularly in Africa. Are genetically modified organisms the way to go? We should research the issues carefully and take decisions based on good science, argues Melodie McGeoch. et’s admit it: many of us have preconceived notions of the acceptability or otherwise of genetically modified organisms (GMOs) and our opinions are often independent of the facts. They may be born out of an ecocentric worldview, images of Frankenstein and vegetables that glow in the dark, or, alternatively, out of a technocratic faith in successful human dominion over nature. But where do science and South Africa currently stand on the subject of GMOs?

L

A view of the stable

GMOs and the environment Environmental risks of GM crops include the development of resistance or weediness (that is, insect pests become resistant to GM crops, or the GM crop may become a weed because it is resistant to insects and herbicides) and the escape of transgenes into wild or non-GM populations. For example, in experimental trials involving a crop modified with Bt (see Fact File), caterpillar mortality was significantly higher several rows into adjacent non-Bt plants because of gene flow between the GM and non-GM varieties. Clearly, any transgene manipulation that results in increased fitness or tolerance in the recipient organism poses a potential ecological risk.

We don't yet understand the potential environmental risks of GMOs sufficiently well to release these organisms freely Other risks include viral and bacterial recombination (where bacteria and viruses may adopt transgenic DNA) and the creation of new toxins, as well as the impact on biodiversity if farming practices change. In the UK, in the only large-scale field trial that has been conducted to examine the ecological effects of GMOs, the change in farming practices associated with planting GM oilseed rape reduced local biodiversity (equivalent trials with GM maize showed no

reduction in local biodiversity). A key argument touted against anti-GM lobbyists is that GMOs are more environmentally sound than conventional pest management. This may well be true in the short term and in the immediate vicinity of the crop. The form of ecological damage that GMOs could potentially cause, however, is far more persistent than any conventional pesticide impact. There is no turning back if a GMO becomes invasive or if genetic contamination of wild populations occurs.

How much do we know? To date, there is very limited evidence that the impact of GMOs poses a significant threat to the environment. This is not necessarily because there’s no impact, but rather because in many cases insufficient research has been completed (virtually none in South Africa). It may be too early in the adoption of the technology for potential ecological problems to be apparent. Currently, for example, individual GMOs are tested and assessed for specific risks – such as the effect of Bt maize on a non-target butterfly. What has largely not been considered is how these risks and new ones, if they materialize, scale up across entire landscapes and regions planted with one or more GM crops. This kind of information is particularly pertinent for us, because South Africa is climatically and socio-economically unique, and because we are one of the most biodiverse countries in the world. We have a lot to lose if we get it wrong. There is a shortage of research in South Africa (particularly research independent of corporate funding, with its potential vested interests) and we do not yet have an adequate framework for systematically assessing local ecological risks posed by GMOs. South Africa’s legislation on GMOs ranks among the most comprehensive and effective in the world. However, one of its weaknesses to date has been that there’s been no requirement for post-release ▲ ▲

Not all GMOs are the same, so it is not appropriate to label all or any GMO with a blanket ‘good’ or ‘bad’. Each GMO involves a different group of organisms and different genes and has a unique set of potential benefits and risks. The benefits of GM crops, for example, include reduced use of pesticides and herbicides and increased yields (although none of these is guaranteed), which are good for both human and environmental health. Also, insect-resistant GM crops are often more specific in the pests that they target than conventional insecticides, so they cause less harm to beneficial and non-target species. Herbicide-tolerant GM crops can reduce soil tillage levels and this conserves soil and reduces energy use. GMOs also pose a range of potential environmental and health risks. It is important to know that these are only potential risks, of unknown magnitude, and may not be realized in practice. This means that (if the risks are sufficiently low), in the same way that aircraft accidents do not stop us from flying, we do consider using and further developing the technology. The health risks largely include potential allergic responses. Not all GM food products contain GM DNA and obviously only those that do are a potential risk. For example, GM potatoes would contain GM DNA, whereas refined sugar does not. Current legislation ensures that substantial food

safety testing is conducted before products are released for commercial use. Evaluating environmental risk presents more of a challenge because of the broad range and contingency of potential impacts. There are several different types of risk, most of which are relevant to some GMOs only, and, also, in some environments but not in others.

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Viewpoint Q

News Q Bringing science to the people: object lesson for SA?

Fact File

Falling student numbers in the sciences are a worldwide concern and scientists need to engage more in public outreach, say correspondents to the journal Nature. Not only is there insufficient outreach in the USA but in France too, reports Pablo Jensen, who leads the French research agency CNRS’s working group on the popularization of science. Preliminary data on the 10 400 CNRS scientists from mid-2003 to mid-2004 showed that three-quarters of them did no popularization or public outreach activity (such as writing a book or presenting a popular science lecture or poster) during the period. Public outreach efforts, moreover, were unequally distributed: the most active 10% of scientists accounted for 70% of all outreach activity and the top 5% accounted for half. There seemed to be three different sub-populations: the ‘silent majority’ (76% of scientists, who do hardly anything); the ‘open minority’ (21% who carry out some activity once or twice a year); and the ‘semiprofessional popularizers’ (3% of scientists who carry out activities on average six times a year). Age made little difference, but there was variation among fields. The proportion of scientists involved in public outreach varied from 17% for general physics, chemistry, and biology, to 30% for astrophysics, and 41% for social sciences. Across the board, the productivity among the active scientists was constant at close to 2.5 outreach activities a year. The most common of these was speaking at conferences on popular science (25%), followed by writing newspaper articles (23%), and giving radio or television presentations (17%). What’s the solution? Scientists need to understand the importance of doing public outreach, says Jensen – declining student numbers seem to have persuaded more physicists to get involved in the International Year of Physics, for instance. The ‘open minority’ might be encouraged by better access to simple tools for efficient public outreach, while the ‘semiprofessional popularizers’ may need better institutional rewards for this work. Imagine the increase in public interest in science in South Africa if just half of our researchers each contributed just one public outreach activity a year – say, by offering an article to QUEST?

GMOs are also sometimes called transgenics, genetically engineered, or living modified organisms (LMOs). The most common GMOs to have been commercially released include crops that are either insect-resistant or herbicide-tolerant. Insect-resistant (or Bt ) GMOs contain toxin genes derived from a bacterium called Bacillus thuringiensis (or Bt ). Bt insecticidal toxin is expressed by all the cells of a plant and different strains affect moths, butterflies, flies, and beetles. The most widely planted GMO crops, globally and in South Africa, are soybean, maize, cotton, and canola (oilseed rape). South Africa is among the top 10 countries worldwide in total hectares planted with GM crops. South Africa's legislation relevant to GMOs includes the Genetically Modified Organisms Act (No. 15 of 1997 and GMO Amendment Bill of 8 October 2004) and the National Environmental Management: Biodiversity Act (No. 10 of 2004). The Cartagena Protocol on Biosafety aims to ensure the safe and responsible development, handling, use, transfer, and release of GMOs. It is a legally binding international agreement to which South Africa acceded in 2003 (see www.biodiv.org/biosafety). ▲

Reported in Nature (21 April 2005).

Genetic modification, involved in the production of genetically modified organisms (GMOs), is the transfer of DNA from one type of organism to another so that the recipient expresses characteristics normally associated with the donor.

environmental monitoring. Without careful, ongoing observations of GMOs that have been released into the environment, we will have no early warning should problems arise. It is hoped that the Biodiversity Act of 2004 will soon bring about the development and implementation of a South African framework for ecological risk assessment. This framework will continually need updating as new GMOs are developed, as older GM technology is modified, discarded, or replaced (to address risks, for example), and as new research findings appear. It is not worth risking long-term damage with a technology that is not sustainable (because insect resistance or weed tolerance could develop, for instance), or with one that may soon be replaced by more acceptable alternatives. This is the rationale for promoting scrupulous environmental risk assessment before the release and commercialization of a GMO.

Placing your bets We don’t yet understand the potential environmental risks of GMOs sufficiently well to release these organisms freely, particularly in the South African context. We know, however, that GMOs are not a panacea for a poisoned environment and starving world: they are a new technology with benefits and with risks. And, most important, they are a technology whose benefits are better understood and appreciated than the risks. This is because the benefits are local, virtually immediate, and therefore clear, whereas the ecological risks are diffuse, longer-term, and consequently more difficult to appreciate. In short, GMOs represent a risk-taking use of

the commons*, and our history of exploiting the commons has not been bright. So, like wise punters, before laying our bets and watching the horses dash from the stalls, we should establish just what the odds are, both for this race and future ones. Unlike horseracing, we’re exploring virgin territory and can’t select our winners based on past performance. But we needn’t remain ignorant of the odds, because science is able to provide accurate and reliable guidance. It must be given the time and opportunity to do so adequately. ■ Professor McGeoch is a member of the Centre for Invasion Biology, and in the Department of Entomology, University of Stellenbosch. Her research background is in plant–insect interactions and insect conservation. For details, consult J. Pretty, “The rapid emergence of genetic modification in world agriculture: contested risks and benefits” in Environmental Conservation, vol. 28 (2001), pp.248–262 and D. Pilson & H.R. Prendeville, “Ecological effects of transgenic crops and the escape of transgenes into wild populations” in Annual Review of Ecology, Evolution and Systematics, vol. 35 (2004), pp.149–174. There's more on the Internet. Visit www.gmsciencedebate.org.uk (GM Science Review Panel [UK]); www.icgeb.trieste.it/biosafety (International Centre for Genetic Engineering and Biotechnology); www.unep.ch/biosafety (United Nations Environment Programme); www.biodiv.org/biosafety Cartagena Protocol on Biosafety); http://biotech.jrc.it (European Commission Directorate General Joint Research Centre); www.epa.gov/eerd/BioTech.htm (US Environmental Protection Agency); www.bma.org.uk/ap.nsf/Content/LIBGenetically ModifiedFood (British Medical Association); www.defra.gov.uk/environment/gm/eu (UK Department for Environment Food and Rural Affairs).

* The 'commons' are resources used by everyone, such as air, water, and services provided by biodiversity (e.g. crop pollination). Humans have a history of inequitable sharing and abuse of these commons.

34 Quest 1(4) 2 0 0 5


Q Viewpoint

Backing the GMO horse: what are the odds The race is on to provide risk-free food for growing human populations, particularly in Africa. Are genetically modified organisms the way to go? We should research the issues carefully and take decisions based on good science, argues Melodie McGeoch. et’s admit it: many of us have preconceived notions of the acceptability or otherwise of genetically modified organisms (GMOs) and our opinions are often independent of the facts. They may be born out of an ecocentric worldview, images of Frankenstein and vegetables that glow in the dark, or, alternatively, out of a technocratic faith in successful human dominion over nature. But where do science and South Africa currently stand on the subject of GMOs?

L

A view of the stable

GMOs and the environment Environmental risks of GM crops include the development of resistance or weediness (that is, insect pests become resistant to GM crops, or the GM crop may become a weed because it is resistant to insects and herbicides) and the escape of transgenes into wild or non-GM populations. For example, in experimental trials involving a crop modified with Bt (see Fact File), caterpillar mortality was significantly higher several rows into adjacent non-Bt plants because of gene flow between the GM and non-GM varieties. Clearly, any transgene manipulation that results in increased fitness or tolerance in the recipient organism poses a potential ecological risk.

We don't yet understand the potential environmental risks of GMOs sufficiently well to release these organisms freely Other risks include viral and bacterial recombination (where bacteria and viruses may adopt transgenic DNA) and the creation of new toxins, as well as the impact on biodiversity if farming practices change. In the UK, in the only large-scale field trial that has been conducted to examine the ecological effects of GMOs, the change in farming practices associated with planting GM oilseed rape reduced local biodiversity (equivalent trials with GM maize showed no

reduction in local biodiversity). A key argument touted against anti-GM lobbyists is that GMOs are more environmentally sound than conventional pest management. This may well be true in the short term and in the immediate vicinity of the crop. The form of ecological damage that GMOs could potentially cause, however, is far more persistent than any conventional pesticide impact. There is no turning back if a GMO becomes invasive or if genetic contamination of wild populations occurs.

How much do we know? To date, there is very limited evidence that the impact of GMOs poses a significant threat to the environment. This is not necessarily because there’s no impact, but rather because in many cases insufficient research has been completed (virtually none in South Africa). It may be too early in the adoption of the technology for potential ecological problems to be apparent. Currently, for example, individual GMOs are tested and assessed for specific risks – such as the effect of Bt maize on a non-target butterfly. What has largely not been considered is how these risks and new ones, if they materialize, scale up across entire landscapes and regions planted with one or more GM crops. This kind of information is particularly pertinent for us, because South Africa is climatically and socio-economically unique, and because we are one of the most biodiverse countries in the world. We have a lot to lose if we get it wrong. There is a shortage of research in South Africa (particularly research independent of corporate funding, with its potential vested interests) and we do not yet have an adequate framework for systematically assessing local ecological risks posed by GMOs. South Africa’s legislation on GMOs ranks among the most comprehensive and effective in the world. However, one of its weaknesses to date has been that there’s been no requirement for post-release ▲ ▲

Not all GMOs are the same, so it is not appropriate to label all or any GMO with a blanket ‘good’ or ‘bad’. Each GMO involves a different group of organisms and different genes and has a unique set of potential benefits and risks. The benefits of GM crops, for example, include reduced use of pesticides and herbicides and increased yields (although none of these is guaranteed), which are good for both human and environmental health. Also, insect-resistant GM crops are often more specific in the pests that they target than conventional insecticides, so they cause less harm to beneficial and non-target species. Herbicide-tolerant GM crops can reduce soil tillage levels and this conserves soil and reduces energy use. GMOs also pose a range of potential environmental and health risks. It is important to know that these are only potential risks, of unknown magnitude, and may not be realized in practice. This means that (if the risks are sufficiently low), in the same way that aircraft accidents do not stop us from flying, we do consider using and further developing the technology. The health risks largely include potential allergic responses. Not all GM food products contain GM DNA and obviously only those that do are a potential risk. For example, GM potatoes would contain GM DNA, whereas refined sugar does not. Current legislation ensures that substantial food

safety testing is conducted before products are released for commercial use. Evaluating environmental risk presents more of a challenge because of the broad range and contingency of potential impacts. There are several different types of risk, most of which are relevant to some GMOs only, and, also, in some environments but not in others.

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Viewpoint Q

News Q Bringing science to the people: object lesson for SA?

Fact File

Falling student numbers in the sciences are a worldwide concern and scientists need to engage more in public outreach, say correspondents to the journal Nature. Not only is there insufficient outreach in the USA but in France too, reports Pablo Jensen, who leads the French research agency CNRS’s working group on the popularization of science. Preliminary data on the 10 400 CNRS scientists from mid-2003 to mid-2004 showed that three-quarters of them did no popularization or public outreach activity (such as writing a book or presenting a popular science lecture or poster) during the period. Public outreach efforts, moreover, were unequally distributed: the most active 10% of scientists accounted for 70% of all outreach activity and the top 5% accounted for half. There seemed to be three different sub-populations: the ‘silent majority’ (76% of scientists, who do hardly anything); the ‘open minority’ (21% who carry out some activity once or twice a year); and the ‘semiprofessional popularizers’ (3% of scientists who carry out activities on average six times a year). Age made little difference, but there was variation among fields. The proportion of scientists involved in public outreach varied from 17% for general physics, chemistry, and biology, to 30% for astrophysics, and 41% for social sciences. Across the board, the productivity among the active scientists was constant at close to 2.5 outreach activities a year. The most common of these was speaking at conferences on popular science (25%), followed by writing newspaper articles (23%), and giving radio or television presentations (17%). What’s the solution? Scientists need to understand the importance of doing public outreach, says Jensen – declining student numbers seem to have persuaded more physicists to get involved in the International Year of Physics, for instance. The ‘open minority’ might be encouraged by better access to simple tools for efficient public outreach, while the ‘semiprofessional popularizers’ may need better institutional rewards for this work. Imagine the increase in public interest in science in South Africa if just half of our researchers each contributed just one public outreach activity a year – say, by offering an article to QUEST?

GMOs are also sometimes called transgenics, genetically engineered, or living modified organisms (LMOs). The most common GMOs to have been commercially released include crops that are either insect-resistant or herbicide-tolerant. Insect-resistant (or Bt ) GMOs contain toxin genes derived from a bacterium called Bacillus thuringiensis (or Bt ). Bt insecticidal toxin is expressed by all the cells of a plant and different strains affect moths, butterflies, flies, and beetles. The most widely planted GMO crops, globally and in South Africa, are soybean, maize, cotton, and canola (oilseed rape). South Africa is among the top 10 countries worldwide in total hectares planted with GM crops. South Africa's legislation relevant to GMOs includes the Genetically Modified Organisms Act (No. 15 of 1997 and GMO Amendment Bill of 8 October 2004) and the National Environmental Management: Biodiversity Act (No. 10 of 2004). The Cartagena Protocol on Biosafety aims to ensure the safe and responsible development, handling, use, transfer, and release of GMOs. It is a legally binding international agreement to which South Africa acceded in 2003 (see www.biodiv.org/biosafety). ▲

Reported in Nature (21 April 2005).

Genetic modification, involved in the production of genetically modified organisms (GMOs), is the transfer of DNA from one type of organism to another so that the recipient expresses characteristics normally associated with the donor.

environmental monitoring. Without careful, ongoing observations of GMOs that have been released into the environment, we will have no early warning should problems arise. It is hoped that the Biodiversity Act of 2004 will soon bring about the development and implementation of a South African framework for ecological risk assessment. This framework will continually need updating as new GMOs are developed, as older GM technology is modified, discarded, or replaced (to address risks, for example), and as new research findings appear. It is not worth risking long-term damage with a technology that is not sustainable (because insect resistance or weed tolerance could develop, for instance), or with one that may soon be replaced by more acceptable alternatives. This is the rationale for promoting scrupulous environmental risk assessment before the release and commercialization of a GMO.

Placing your bets We don’t yet understand the potential environmental risks of GMOs sufficiently well to release these organisms freely, particularly in the South African context. We know, however, that GMOs are not a panacea for a poisoned environment and starving world: they are a new technology with benefits and with risks. And, most important, they are a technology whose benefits are better understood and appreciated than the risks. This is because the benefits are local, virtually immediate, and therefore clear, whereas the ecological risks are diffuse, longer-term, and consequently more difficult to appreciate. In short, GMOs represent a risk-taking use of

the commons*, and our history of exploiting the commons has not been bright. So, like wise punters, before laying our bets and watching the horses dash from the stalls, we should establish just what the odds are, both for this race and future ones. Unlike horseracing, we’re exploring virgin territory and can’t select our winners based on past performance. But we needn’t remain ignorant of the odds, because science is able to provide accurate and reliable guidance. It must be given the time and opportunity to do so adequately. ■ Professor McGeoch is a member of the Centre for Invasion Biology, and in the Department of Entomology, University of Stellenbosch. Her research background is in plant–insect interactions and insect conservation. For details, consult J. Pretty, “The rapid emergence of genetic modification in world agriculture: contested risks and benefits” in Environmental Conservation, vol. 28 (2001), pp.248–262 and D. Pilson & H.R. Prendeville, “Ecological effects of transgenic crops and the escape of transgenes into wild populations” in Annual Review of Ecology, Evolution and Systematics, vol. 35 (2004), pp.149–174. There's more on the Internet. Visit www.gmsciencedebate.org.uk (GM Science Review Panel [UK]); www.icgeb.trieste.it/biosafety (International Centre for Genetic Engineering and Biotechnology); www.unep.ch/biosafety (United Nations Environment Programme); www.biodiv.org/biosafety Cartagena Protocol on Biosafety); http://biotech.jrc.it (European Commission Directorate General Joint Research Centre); www.epa.gov/eerd/BioTech.htm (US Environmental Protection Agency); www.bma.org.uk/ap.nsf/Content/LIBGenetically ModifiedFood (British Medical Association); www.defra.gov.uk/environment/gm/eu (UK Department for Environment Food and Rural Affairs).

* The 'commons' are resources used by everyone, such as air, water, and services provided by biodiversity (e.g. crop pollination). Humans have a history of inequitable sharing and abuse of these commons.

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Q Careers in S&T

Engineers

in a big industry

Here are some openings if you want to work for a multinational organization involved in resources and beneficiation. To start – consider what skills the country needs ■ the 2010 soccer World Cup in South Africa means construction work and a need for civil engineers ■ economic growth needs mineral resources – such as platinum, chrome, copper – so there are openings for mining engineers, particularly in Africa ■ large global industrial organizations need people who are good at exploration, research, and keeping businesses going. Big companies dealing in resources – such as mining houses or industrial operations – need many different types of people and skills. In the fields of engineering, you could take a degree and register, in due course, as a professional engineer. Or you could qualify as a technician (acting as a link between engineers and those who operate processing plants and solving technical problems) or as a technologist (working directly with production and operating production processes).

Chemical engineering Chemical engineers design and operate the processes that turn raw materials, such as coal, into useful chemical products that we all use every day – for instance, paints, solvents, wax, acrylic, and countless others. Working on plants and in advanced chemical engineering technologies, a chemical engineer evaluates different processes in the search for ways to manufacture new chemical products and improve efficiency. The work can also involve designing and commissioning plants – to produce fuels and chemicals, for example. This career path is for people who are interested in the way in which equipment and machinery work. It takes place in design offices, laboratories, and processing plants. Matric subjects include chemistry, mathematics, physical science.

Electrical engineering Electrical engineers work with electrical equipment. An electrical engineer working in heavy current electrical engineering, for example, typically focuses on voltages between 110 V and 123 kV and equipment such as generators, motors, transmission lines, cables, transformers, switchgear, substations, and lighting. As an electrical engineer you ■ design, manufacture, install, maintain, operate, and manage electrical equipment and installations that generate, distribute, and utilize electrical power ■ design, engineer, construct, and commission new electrical facilities ■ optimize and modify existing electrical facilities as required (e.g. to improve reliability) ■ manage electrical projects from feasibility phase to commissioning. Matric subjects include mathematics, physical science, technical drawing.

Mining engineering Mining engineers work all over the world, so it’s a profession for people looking for travel opportunities. The job involves planning, designing, constructing, and operating mine facilities, as well as managing mining activities so that they work efficiently and safely. Mining engineers start with an interest in geology and how the earth was formed. They must know how to reach the riches below the ground and extract them, and they need to understand the risks. They are responsible for the entire process – selecting the right place to blast, extracting the right kind of ore, loading it, and getting it to the surface. Mines are huge financial investments, so they need people who are practical and have an eye for detail. Mining engineers need to be able to get on well with the variety of people who work on a mine and be able to accept different points of view. Work can be rough at the rock face but, says one mining engineer, “It’s very rewarding, because you’re doing a job that’s ‘real’ and that produces something valuable and tangible. There’s dust and sweat – but nothing feels better than that hot shower at the end of a shift!” Matric subjects include mathematics, physical science, as well as chemistry and geography.

Young engineers studying an engineering drawing. Photograph: Courtesy of Sasol

Other openings Mechanical engineers work with and maintain equipment (e.g. pressure vessels, piping systems, pumps, compressors, turbines, fans, and boilers). Industrial engineers are vital for expanding business and improving operations. They evaluate and improve industrial systems, for instance, and are involved in researching, developing, and managing the supply chain, making sure that systems work as efficiently as possible. Geologists and geophysicists in mining gather and interpret exploration data and information from contract areas. Metallurgists optimize and control the efficiency of mineral beneficiation and metal extraction in metallurgical plants. Logistics management involves buying, manufacturing, distributing, and selling feedstock and products. It includes planning and managing purchases, distribution, warehouse/operations, materials handling, and packaging, as well as customer service and orders. Information management/informatics focuses on managing the IT environment to ensure access to information. ■

QUEST thanks Sasol Corporate Graduate Services for advice and information, as well as Dr Olla van der Walt (of TWP Consulting) and the late Dr Andrew Patterson.

A case study Sasol is an oil and gas company with chemical interests. This kind of large industrial organization gives you an idea of the variety of products – and skills – that are involved in the energy, fuels, chemicals, and related sectors. Starting with coal, Sasol produces solvents, plastics, fibres, explosives, fertilisers, waxes, and a wide range of fuels. Applying innovative and competitive technologies to excel in selected markets, the company has some 31 000 employees worldwide – predominantly in Africa – and says: “We are constantly searching for top achievers who share our entrepreneurial spirit and vision of further developing our company into a highly respected global enterprise.”

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Q Your Q UEST ions answered QUESTION Does new DNA research affect taxonomy and the identification of species and will it mean changes in our current classifications?

?

DNA and taxonomy ANSWER It already has. For example, research conducted by students, colleagues, and myself has demonstrated that many southern African bird species currently recognized as a single species are in fact two or more species. Based on a combination of anatomical, behavioural, and DNA-based evidence, for instance, the black korhaan (Eupodotis afra) has now been split into two species, the northern black korhaan (afraoides) and southern black korhaan (afra); and the olive thrush (Turdus olivaceus) also into two, the olive thrush (olivaceus) and Karoo thrush (smithi). Indeed, the list of species of birds for southern Africa might increase by as much as 25% once further research of this kind has been conducted. The opposite has also been the case since recent DNA-based research has shown decisively that the imperial pheasant (Lophura imperialis) from Vietnam is not in fact a separate species but a hybrid between the silver pheasant (L. nycthemera) and Edward’s pheasant (L. edwardsi). Perhaps the most exciting discovery, however, is that the nearest evolutionary relative of the rock jumpers (Chaetops frenatus) one sees jumping from rock to rock in Sir Lowry’s Pass in the Western Cape is the white-necked rockfowl (Picathartes oreas), a cave dweller from west-central Africa, and that these two species split off from the bird tree of life perhaps as long as 50 million years ago. Professor Timothy Crowe, Percy FitzPatrick Institute, University of Cape Town

ANSWER In short, the answer to this question is a resounding ‘yes’. DNA research has already influenced much of our thinking about species limits and biological classification. At a relatively basic level, DNA sequence data have helped us to disentangle problematic complexes of cryptic species in which there has been very little evolutionary change in physical appearance, while changes at the gene level have been so significant as to result in the origin of new species. This doesn’t necessarily help us with the identification of

the living organisms in the field – the cryptic species don’t wear DNA bar codes that we can scan at a glance! – so bird watchers may still have problems telling one lark or pipit from another. At a deeper level, DNA can provide valuable data regarding the grouping and relationships of living organisms, which, in turn, helps us to construct more meaningful classification. In the same way as forensic scientists use DNA to help to solve murder mysteries, we can also use it to unravel problems related to classification. As an example, one genus of South African snails, Prestonella, had represented a taxonomic enigma for many decades. Only empty shells were available, and we had no clue to which family it belonged nor, therefore, how it should correctly be classified. Taxonomists had shuffled it from one family to another, but largely using guesswork. At last we managed to find living examples and were able to study the animal itself, including its DNA. Very quickly, the DNA sequences gave us new data indicating that these snails are unique on the African continent and are more closely related to species living in Australasia and South America than to other African snails. They originated in the ancient supercontinent of Gondwana and have been separated from their closest relatives for more than 100 million years. We have now confirmed this conclusion by the much more laborious process of comparing the internal anatomy, but it was the DNA that gave us the initial insight and enabled us to solve this molluscan mystery. Dr Dai Herbert, Head of the Department of Mollusca, Natal Museum, Pietermaritzburg Send your questions to The Editor (write S&T QUESTION in the subject line) by e-mail to editor.quest@iafrica.com OR by fax to (011) 673 3683. Please keep them as short as possible, and include your name and contact details. (We reserve the right to shorten or edit for clarity.) We will send you R50 for every question that we publish with answers from our experts.

Q Measuring up Odd measurements

very thick chocolate to form into balls and hand dip, it would probably need a viscosity of about 190°McM.

How do you measure...

... the age of your dog? A dog’s age is measured in dog years, an informal unit of time equal to 1/7 of a ‘human’ year.

... your ‘fatness’? Your body mass index (BMI) measures your ‘fatness’. It is equal to your weight (W ) in kilograms divided by the square of your height (h) in metres (W/h2 ). Generally, an adult with a BMI less than 20 kg/m2 is considered to be ‘underweight’, 25–29 kg/m2 ‘overweight’, and 30 kg/m2 or more ‘obese’. ... the thickness of chocolate? To measure the thickness, or viscosity, of chocolate, you would use a MacMichael viscometer. The measurement is in degrees MacMichael (°McM). Chocolate with a viscosity of 60°McM would be very thin and suitable for pouring into moulds. If you wanted

... a patient’s smoking history? Smoking is measured in pack years. One pack year is equivalent to smoking 7 300 cigarettes a year, or one pack of 20 a day. ... a unit of human blood? A unit of human whole blood is 450 millilitres in volume. For components of blood or blood products, one unit is the amount of that substance that would normally be found in one unit of whole blood. The adult human body contains roughly 12 units of whole blood.

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“Albert Einstein explains his theory of general relativity in Paris in 1922” (according to the description on the back of the canvas). 123  182 cm. Oil. Reproduced from the original painting by Harold Voigt (c. 2005) by kind permission of the artist.

Fifty years ago, on 18 April 1955, Albert Einstein died in Princeton, New Jersey. To commemorate this extraordinary life, we asked South African artist Harold Voigt about his painting of Einstein.

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hat gave you the idea for this painting?

W

The idea for a painting had been in the back of my mind for some time but it was only when I saw again a photograph I’d first seen years ago of Einstein addressing a group of physicists in Paris in 1922, the year after he’d been awarded the Nobel Prize in Physics1, that the idea began to take form.

The photograph (I think it might have been published in Time magazine) showed Einstein before a large blackboard, chalk in hand, explaining some theory to an enraptured audience. The blackboard was covered in symbols, diagrams, equations, erasures, smudges. Einstein’s universe, in all its cryptographic splendour, was alone subject enough for a painting. The background darkness of the


Q News

Q Interview The Sombrero galaxy through different eyes

blackboard symbolized time/space/ eternity, the chalk marks scrawled across the surface evoked thoughts of revelation – ‘The Moving Finger writes; and, having writ, Moves on....’ (Rubaiyat of Omar Khayyam) And before the blackboard, the great explorer/voyager himself, confident that he’d grasped the truth – keen to share his discovery – not without a little showmanship. (Einstein, the conjurer, the wizard, the Seer.) Like Moses, he’d been to the mountain and brought down the tablets. I decided to translate/transmogrify this image into a painting, not really knowing where the process would take me.

How did you approach the task? My main concern was with the integrity of the picture plane2. The various elements would have to live together harmoniously, yet within a state of tension – but still allow for the expression of the painter’s own style or signature. In my case this has to do with a certain colour and tonal sensibility, a need to explore the plastic possibilities of the mixed media being employed3 ... and then [there was] the problem of how to treat the figure of Einstein. I wanted him to be immediately recognizable but not a caricature. His position on the canvas, and the area he occupied relative to the other elements and to the overall picture were important4. Using various photographic references sourced mainly from books, magazines, and the Internet, I constructed the figure, paying considerable attention to posture, clothing, facial expression, and hand gesture5. As work progressed, it became clear that the face was not going to be readily identifiable. Problem was that, in 1922, Einstein was 43 years old and his hair was still dark – almost black. When I changed the colour of the hair to silvery grey and made it unkempt, he was immediately transformed into the Einstein so familiar to the world. Call it artistic licence.

The picture was never intended to be a documentary record of an important event that took place in Paris in 1922. It should rather be seen as an imagined interpretation of what happened at that time. I would hope that the picture evokes in the viewer’s mind a sense of marvel, enigma, and magnificent revelation, and indeed that is what Albert Einstein has always meant to me. The work took place over a period of about three months between October 2004 and January 2005, with changes constantly being made. The palate was pared down to a range of warm and cool greys to enhance the sense of period. A strong cobalt blue was introduced fairly late to intensify the feeling of receding space behind the chalk marks on the blackboard. ■ Born and educated in Johannesburg, Harold Voigt studied architecture, embarked on a brief career in advertising and film making, and then, in 1971, made painting his fulltime profession. He designed and built a home on a mountain in the eastern lowveld of Mpumalanga, where he works and lives with his wife, Leigh, also an artist. He exhibits nationally and internationally. He is represented by the Everard Read Gallery in Johannesburg and Cape Town.

Astronomers use different telescopes, sensitive to different wavelengths (parts of the electromagnetic spectrum), to obtain different information about luminous objects. Two different telescopes – NASA’s Spitzer and Hubble Space Telescopes – using a variety of filters, observed the Sombrero galaxy and showed it up in different ways. Then, joining forces, they created a striking composite image. Messier 104, one of the most popular sights in the Universe, is nicknamed the Sombrero galaxy because, in visible light, it looks like the broad-rimmed Mexican hat. In Hubble’s visible light image, only the near rim of dust can be clearly seen in silhouette, but recent observations using Spitzer’s infrared array camera uncovered the bright, smooth ring of dust circling the galaxy (shown in red). Spitzer’s infrared view of the starlight, piercing through the obscuring dust, is easily visible, along with the bulge of stars and an otherwise hidden disk of stars within the dust ring. Spitzer’s full view shows that the disk is warped, which is often the result of a gravitational encounter with another galaxy, and clumpy areas spotted in the far edges of the ring indicate young star-forming regions. The Sombrero galaxy is about 28 million light-years away. Viewed from Earth, it is just six degrees south of its equatorial plane. Spitzer detected infrared emission not only from the ring, but from the centre of the galaxy as well, where there is a huge black hole, believed to be a billion times more massive than our Sun. This magnificent galaxy has a diameter that is nearly one-fifth the diameter of the full Moon. Pictures: Infrared: Courtesy of NASA/JPL-Caltech/R. Kennicutt (University of Arizona), and the SINGS Team. Visible: Courtesy of Hubble Space Telescope/Hubble Heritage Team

For more, visit www.everard-read.co.za 1 In 1922 Einstein received the 1921 Nobel Prize in Physics “for the photoelectric law and his work in the domain of theoretical physics.” In 2005, the world celebrates the International Year of Physics and the centenary of Einstein’s annus mirabilis (1905) during which he published five key papers.

Composite image.

2 The integrity of the picture plane This has to do with making sense of the two-dimensional space on the canvas on which the artist is working. It has no actual physical depth, so the artist has to work out how to restructure the complexity of shape, form, colour, and tone onto that single plane. “It’s like a puzzle, and you have to find ways to fit all the pieces together,” says Voigt. 3 plastic possibilities of the mixed media being employed Voigt works in several media at a time (that is, acrylic, linseed oil, and wax). The artist is like an alchemist, he explains, “mixing the media together to make something new.” While the ingredients are still pliable, he “adds the medium, scrapes some of it off, pulls it around, and experiments with the materials.”

Hubble’s visible light image.

4 the area he occupied relative to the other elements and to the overall picture This refers to a kind of ‘artistic’ relativity, where it is important to strike the right balance between the central subject (the man Einstein himself) and his environment – to show the relative importance of the different elements in the picture. 5 attention to posture, clothing, facial expression, and hand gesture These show the artist’s feeling about the way in which Einstein might have explained himself. Says Voigt, “Here science and art part ways: I’m using the art route – freedom of expression – for the drama and the theatre of Einstein as the grand actor on stage.”

Spitzer’s infrared image.

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Books Q Cotyledon and Tylecodon By Ernst van Jaarsveld and Daryl Koutnik; illustrations by Elise Bodley and Lisa Strachan (Pretoria: Umdaus Press, 2004). ISBN 1 919766 32 4

outhern Africa has the world’s largest concentration of succulent plants and their strange, often stark and bold shapes are admired the world over. This book is for everyone interested in plants and botanical art, from the lay person and succulent enthusiast to the horticulturist and botanist. It is the first full-colour popular account of all 57 known members of the Cotyledon (11 species) and Tylecodon (46 species) genera, two closely related plant groups, found almost exclusively on this subcontinent. Author Ernst van Jaarsveld wanted readers to recognize the richness of our succulent plant flora “and to realize that by growing these plants anyone can become part of ex situ conservation of rare species. The rankplakkie (Cotyledon adscendens), for instance, grows in coastal thicket around Port Elizabeth and

S

Cotyledon pendens grows on cliff faces, and is ideal for planting on embankments and stone walls and in hanging baskets.

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Tylecodon reticulatus subsp. reticulatus

urban development threatens its longterm survival. It grows very easily from cuttings (as do most Cotyledons and Tylecodons) and we can conserve it just by growing it in our gardens.” Cotyledon and Tylecodon genera belong to the world’s third largest succulent plant family, the stonecrop family (Crassulaceae – ‘crassus’ means ‘fat’). The book’s introduction describes their adaptation to arid environments, their distribution in Africa, ways to cultivate them, ethnic uses, and the history of their botanical exploration. The individual and fully illustrated species accounts are arranged alphabetically. Internationally, both genera, especially Cotyledon, are horticulturally well known as garden ornamentals, especially in rockeries or as greenhouse specialities. They range from the 3-metre-high botterboom (Tylecodon paniculatus, which looks like a miniature baobab) and the common pig’s ear (Cotyledon orbiculata) to the dwarf, well-camouflaged Tylecodon occultans. Cotyledons are appreciated for their resistance to drought, large and attractive ornamental foliage (grey to green), and colourful tubular flowers, which attract birds. Tylecodons have been grown in England as greenhouse

plants since 1759. Says van Jaarsveld, “The demand for the plants and for information about them is greater elsewhere than in our own country!” Linnaeus described Cotyledon in 1753 and, in the 1970s, Helmut Toelken split the genus in two, keeping the evergreens with leaves in opposite pairs within Cotyledon and characterizing the new genus Tylecodon (an anagram of Cotyledon) as the summer deciduous species with spirally arranged leaves. Tylecodon grows in winter rainfall areas and is a genus of stem and leaf succulents; Cotyledon grows throughout South Africa and is a genus of mainly leaf succulents. This update tries to “popularize the information (without losing the science)”, explains van Jaarsveld. Both genera contain a poison that causes cotyledonosis, or ‘krimpsiekte’, which kills livestock in the Karoo if they graze on it. But there are medicinal uses too – in South Africa, the leaves of Cotyledon orbiculata are often applied to remove corns and warts and the sap is sometimes used as a gargle for sore throats or as a poultice for abscesses. The popular Afrikaans name ‘plakkie’ (meaning ‘to stick’), explains van Jaarsveld, comes from the sliced leaves used on warts or


Q Books New books The Science of Discworld III: Darwin’s Watch. By Terry Pratchett, Ian Stewart, and Jack Cohen (Ebury Press). ISBN 0 091898 23 4 This fictional story, set in Discworld (on the back of a giant turtle) is a fine excuse for exploring serious, modern science. The first book of the series saw Discworld wizards accidentally create our universe, Roundworld. Now they intervene to make sure that Charles Darwin successfully writes his On the Origin of Species rather than allow creationism to triumph. Extensive footnotes by science writers Ian Stewart and Jack Cohen explain Darwin’s theories, updating them for modern times, and the book takes the reader through subjects that include relativity, infinity, and time travel. In his New Scientist review, Stephen Baxter describes it as “an earnest and conscientious educational project, a fun book which deserves to be taken very seriously indeed.”

The Sun: A biography. By David Whitehouse (John Wiley). ISBN 0 470092 96 3

Above: Tylecodon paniculatus in Namaqualand. It is known as ‘botterboom’ (or ‘buttertree’) because of its soft, juicy stems. This plant is pollinated by sunbirds. It grows well in cultivation but must be kept dry in summer. Below: Tylecodon faucium habitat (with Aloe claviflora) in the southern Karoo. This dwarf succulent is best grown as a potplant.

abscesses. Xhosa people use the warmed leaf juices to relieve ear or toothache, and, among Zulus and Swazis, the leaf sap is used as an enema for treating syphilis. The challenges, says van Jaarsveld, included finding the plants, cultivating them, and, when they flowered, “getting them to the artist in time to prepare a plate”. Expeditions were arranged to collect specimens that were not available, with cultivation as the crucial “long-term living investment from which we ‘harvest’ information”. For this project, Van Jaarsveld recruited Daryl Koutnik from California in the USA (who was working at the University of Cape Town’s Bolus Herbarium in the mid1980s) and award-winning South African botanical artist, Elize Bodley. As the plants in the collection of the Kirstenbosch National Botanical Garden in Cape Town flowered, she illustrated them and, after she died in 1997, Lisa Strachan spent two years completing the work. The cliff dwellers had never been illustrated before and Strachan enjoyed the rarer plants, “especially those full of minute detail. Nature almost dares the artist to

try to reproduce a likely duplicate of what she has produced!” She revelled in trying to “capture the plants” and her illustrations won a Silver Gilt medal at London’s Royal Horticultural Society Winter 2004 exhibition. Van Jaarsveld’s 25-year “great adventure” was driven by his passion to find the right plants and prepare the book. Some species were camouflaged or grew in inaccessible sites. “Time, effort (climbing mountains, rubber canoes), and research become a pleasure and a way of life. Sometimes the camera becomes wet, you lose equipment on a dangerous rapid, you get lost in the field, or attacked by bees. [But] the more you understand the group and how it operates and fits into the plant kingdom, the more you love it, and you keep on till all the species are worked through. We have the world’s richest flora,” he concludes, “it’s important to conserve it for our children.” This beautiful book is a valuable contribution in helping to make this happen. ■ For details, visit the Umdaus Press at www.succulents.net or e-mail afick@iafrica.com or phone (011) 880 0273.

Offering encyclopaedic coverage, this history presents the science, hypotheses, myths, and anecdotes associated with the Sun. Its author has gathered together into one volume such nuggets as the speculations of the Greek philosopher Anaxagoras (who thought the Sun was a huge ball of red-hot iron) and William Herschel (who thought that living creatures resided in it). He also covers facts, theories, and complexities of our own time such as those dealing with the sunspot cycle, auroras, solar neutrinos, and coronal heating, as well as the Sun’s birth and the way astronomers think it will die some time in the future. What Einstein said and wrote The International Year of Physics has already yielded important publications about Einstein and his work. Two that bring readers close to his personality and thinking are a set of recordings that he made and a new volume of his letters. Albert Einstein: Historic recordings (London: British Library Publishing. ISBN 0 712305 21 1) is an audio CD in which Einstein engages with George Bernard Shaw; supports the Refugee Assistance Fund in London’s Royal Albert Hall; discusses the “common language of science” on radio; and answers the question “Why does E = mc2?” in a 1947 film recording. The Collected Papers of Albert Einstein, Volume 9. The Berlin Years: Correspondence, January 1919–April 1920. By Albert Einstein and translated by Ann Hentschel. (Princeton University Press. ISBN 0 691121 24 9) This most recent volume of Einstein’s letters covers the time that the 40-year-old physicist became an instant celebrity after the apparent verification of his theory of general relativity and also experienced serious personal upheavals to do with his marriages and his mother’s death.

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Pictures: Courtesy of Sun City

Sun City’s golf courses are irrigated with recycled water. Above: The Gary Player golf course. Below: The Lost City golf course with its deliberately economical desert-style design. Only 30 ha of the 55-ha course are watered by sprinklers, yet the trees, fairways, and greens are lush.

Sun City isn’t just glamour, golf, and gaming – it’s also worth a visit for the plants and birds in an ancient volcanic environment and for the Pilanesberg next door.

Nature amid the glitz Volcanic origins The Bojanala region of the North West Province boasts one of South Africa’s outstanding geological attractions: the Pilanesberg Complex. The world’s most clearly defined example of a volcanic alkaline ring complex, it measures 530 km2 and is the second largest of only three. (The largest is on the Kola Peninsula in Russia and the other is in Greenland.) The geology of the mineral-rich Pilanesberg Complex developed out of an ancient volcano that erupted some 1 500 million years ago. The three almost perfectly circular and dissected concentric rings of hills of the complex rise out of flat country. Contrary to popular belief, they are not what is left of the old volcanic crater, but erosion remnants of intrusive ring dykes formed by upwelling magma during and after the volcano’s collapse. They can be observed from the resort of Sun City and the Pilanesberg National Park.

One garden, four climates In the Sun City resort are the 25-hectare Palace gardens, which received botanical garden status in 1998. They boast some 3 200 species of plants and 1.6 million specimens (of which 260 000 are trees), laid out in different ecosystems. Three-quarters of

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the flora is indigenous and there are large specialist species collections of acacias, ficusses, palms, and bauhinias. Each of the four main habitats or regions – representing wet and dry climates (wetlands, dry, coastal, and rainforest) – has its own customdesigned irrigation system. The wetlands region (located above the Palace underground carpark) has an irrigation system maintained by a single ball valve, which operates in a way that is similar to the valve in a lavatory cistern. Once the water level drops below a certain point, the valve opens and more water is added. The dry region’s irrigation, in contrast, is maintained through a timer-sprinkler system. In the dry region is the remarkable baobab forest. It is the most southern point to which baobabs have been removed and successfully transplanted. A sand mountain was constructed to accommodate the trees, and, after the first three began to flourish, it was decided to import 24 more – including 4 large, established baobabs – from a plot of open land in Mpumalanga that had been earmarked for a mango plantation. The trees had unusually deep tap root systems, and roots and branches were severely cut back to

allow the trucks transporting them to Sun City to drive through towns and under power lines. Massive cranes moved them into their final position. The largest baobab in this forest is currently listed in the Guinness Book of Records as the Largest Relocated (in the most southern position) Baobab. It weighs 40 tons and is more than 300 years old. In the coastal vegetation region (at the Valley of Waves) is a specialist collection of about 400 different types of palms, and in the rainfall region (north of the Palace towards the Valley of Waves) there are ebony trees originally from Taiwan, fluted milkwood, and red beech. On the fringes of the botanical gardens and merging with the natural bush are euphorbias from Saudi Arabia and camel thorn from the Kalahari desert.

Birds, fishes, and crocs The plants and climates of the botanical gardens and golf courses attract many birds, and, besides those in the two aviaries, some 190 species have settled here, including hadeda ibis (Bostrychia hagedash), Egyptian geese (Alopochen aegytiaous), grey loeries (Corythaixoides concolor) and redwing starlings (Onychognathus morio). The baobab forest has


Q The S&T tourist indigenous finches, waxbills, bronze mannikins (Spermestes cucullatus), and paradise flycatchers (Terpsiphone viridis). Predators, such as Wahlberg’s eagle (Aquila wahlbergi) and the grey heron (Ardea cinerea), keep rodent and reptile populations under control. The waterways and pools at the Cascades and in the botanical gardens have many kinds of fish including barbell, tilapia, and leatherback carp. More dramatic are the crocodiles bred in the Kwena Gardens crocodile sanctuary. Home to more than 7 000 crocodiles, it includes the three largest captive Nile crocodiles in the world, of which the longest measures 4.7 metres. At the 13th hole of the Lost City golf course are 36 crocodiles that were bred at Kwena – some are nearly two metres long.

Walk the walks Walking the botanical gardens means wandering through all kinds of scenery. The history and origin of all the plants have been meticulously catalogued and the trees display national tree numbers. Designated walks through the forest area (marked on the footpaths) include the Baobab trail, which passes through dry areas of indigenous planting to the baobab forest. The Beach and Crocodile Valley route takes in tropical and coastal plants, and the Spider Web trail takes in exotic and indigenous cycad plantations, tropical rainforest, and jacarandas, with birdlife that includes flamingoes and waterfowl. In contrast, there are the desert plants of the Lost City golf course, such as euphorbias and aloes. Three trees at Sun City have been grown from cuttings from three of South Africa’s most famous trees. One is from Pretoria’s Wonderboom (Ficus salicifolia) or ‘miracle tree’, which is over 1 000 years old, and whose drooping branches took root to produce smaller trunks that now cover an area of 1.5 hectares and branches that can give shade for more than 1 000 people. A second is from the Ultimatum tree, a cluster fig (Ficus sycomorus) near the Tugela river mouth, in whose shade, on 11 December 1878, a British ultimatum to a Zulu delegation in effect demanded the nation’s dissolution; the Zulu refusal to reply sparked the Anglo-Zulu wars. The third is from Mossel Bay’s white milkwood (Sideroxylon inerme) Old Post Office tree from which, in 1500, a Portuguese sailor hung an account of a shipwreck in its branches; for centuries thereafter, sailors left letters in the tree for delivery by others sailing to the required destination.

Waterwise Maintaining forests and golf courses uses water – Sun City as a whole uses some 9 000 m3 of water a day – enough to supply the needs of a small town, but still less than its 12 000 m3 allocation from the Hartbeespoort dam system. The resort is designed to save water, and 2 million litres of water recycled at the Sun City treatment plant are used each day to irrigate the gardens and golf courses. “We don’t have a drop to waste,” said Gary Player when he and his team designed the Lost City golf course, “so the course had to be economical”. Rain sensors in the gardens of the whole resort constantly monitor the level of moisture in the soil. The central sprinkler systems to water the plants are activated only when the Below (from top): Pilanesberg lookout; elephant-back safari; encounter with a lion on a game-viewing drive; walkway in the Palace botanical gardens.

water content in the soil drops below a predetermined benchmark.

The Pilanesberg National Park Next to Sun City is the malaria-free Pilanesberg National Park. Proclaimed a reserve in 1979, it benefited from Operation Genesis, the world’s largest game translocation programme ever undertaken. A big game fence 110 km long and 188 km of roads were constructed and the park now has more than 7 000 animals, including 24 of the larger species, and more than 360 bird species. It is South Africa’s fourth largest national park and covers an area of 55 000 hectares. Located in the transition zone between the dry Kalahari and wetter lowveld vegetation known as ‘bushveld’, the park has unique overlaps of mammals, birds, and vegetation. Springbok, brown hyena, the red-eyed bulbul, and camel thorn trees – normally found in arid areas – cohabit with moist-area-limited impala, black-eyed bulbul, and Cape chestnut trees. The varied topography includes syenite koppies, thickly forested ravines, and bushveld as well as rolling grasslands and lightly wooded areas. Because of its variety of habitats, it has a wider variety of game species than any other similar-sized game reserve in southern Africa, with a high potential for supporting rare and endangered species such as black rhino, roan, sable, tsessebe, foot-and-mouth free buffalo, and wild dogs. Visitors can see the ‘big five’ (lion, leopard, rhino, elephant, and buffalo) as well as cheetah, sable, giraffe, zebra, hippo, crocodiles, sable, tsessebe, springbok, gemsbok, red hartebeest, and many other animals. Throughout the park there are Stone and Iron Age sites. ■ QUEST thanks Professor Faan Coetzee (Tshwane University of Technology) for geological information. For details of Sun City walks contact the Welcome Centre; for the Pilanesberg National Park visit the North West Parks & Tourism Board at www.tourismnorthwest.co.za and www.parksnorthwest.co.za. Contact Gametrackers Outdoor Adventures in the Welcome Centre (or phone [014] 552 5020 or e-mail: suncity@gametrac.co.za) for balloon safaris, elephantback safaris, game drives, and guided hikes in the Pilanesberg National Park. You can drive through the park in your own car and take a self-guided walking trail in the Educational Zone at Manyane. Consult Jacana Media’s Pilanesberg Guide (2004). Plan your game drive by accessing ParkView© for animal sightings in the game office at Bakubung. To check out the night skies at the time of a visit, phone the Johannesburg Planetarium (011) 717 1392. For accommodation try Sun International (www.sun-international.com); Bakubung Bush Lodge and KwaMaritane (www.legacyhotels.co.za). The two Golden Leopard Resorts at Manyane and Bakgatla Camps (www.goldenleopard.co.za) in the park also offer caravan and campsite facilities and, among many other accommodation options in the area, there are fenced camps (some with chalets, some tented only) in the park at Manyane, Bosele, Mankwe, Metswedi, and Kololo.

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Q News

Q Q UEST crossword You’ll find many of the answers in our pages, so it helps to read the magazine before doing the puzzle. 1

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4 Fossilized tree gum (5) 6 Another word for 'information' (3) 8 A skeletal muscle whose contraction bends a joint (6) 9 A virus produces this class of large molecules to mislead our immune systems (7) 11 This type of engineer designs or maintains works of public utility, such as roads and bridges (5) 14 Large spotted feline; one of the Big Five (7) 16 Computer operating system (3) 18 To shed feathers, hair, or skin before a new growth (5) 19 Minute arachnids, which often infest animals or plants (5) 22 The study of the total DNA of a cell (8) 23 Slow-moving gastropod mollusc, usually with a spiral shell (5) 25 Basic microscopic structures of all organisms (5) 27 A type of spider that can live up to 25 years (6) 28 The most common crocodile, widely distributed in Africa (4) 29 Prize in physics won by 17 Down (5) 30 Descriptive of a disease which is present, but not yet developed or manifest (6)

1 Dubious, uncertain (4) 2 A type of starling seen in the Palace botanical gardens (7) 3 The ancient remains or impression of a plant or animal hardened in rock (6) 5 The fourth planet from the sun, red in colour due to the iron-rich minerals covering its surface (4) 6 Machines that separate the seeds from raw cotton fibres (4) 7 Colourless odourless gaseous element, mainly used in fluorescent lamps and advertising signs (4) 10 A widespread outbreak of an infectious disease (8) 12 Type of plant with edible seeds in pods, such as peas, beans, lentils (6) 13 A shape that some churches and spider structures have in common (4) 15 An agent that causes disease (8) 17 Famous German-born physicist; founder of the theory of relativity (8) 20 A group of animals or plants within a genus (7) 21 Sun City has a forest of such trees; Latin name Adansonia digitata (6) 22 A word with the same meaning as worldwide, or pandemic (6) 24 The hadeda ----, a large brown bird with a loud, raucous cry (4) 25 Spiral wire for the passage of an electric current (4) 26 The lower soft pendulous part of the outer ear (4)

Do you like crossword puzzles? Was this one too difficult? Too easy? Just right? Would you also, in addition, like a QUEST competition crossword (with a prize) that is more difficult? Fax The Editor at (011) 673 3683 or e-mail your comments to editor.quest@iafrica.com and let us know. (Mark your message CROSSWORD COMMENT.)

SA support for world’s first Ka-band TT&C satellite When Boeing’s Spaceway F1 satellite took off in April 2005 from Long Beach, California, South Africa’s CSIR provided the launch support for the first-ever Ka-band* telemetry, tracking, and command (TT&C) satellite. The CSIR’s Satellite Applications Centre (SAC) is contracted to support the launches of all three Spaceway satellites – Spaceway F1, F2, and F3 – offering services ranging from telemetry (receiving the satellite’s health status and data) and tracking (following the satellites and sending Boeing the antenna pointing data and ranging information details) to commanding (relaying commands from the Boeing control centre to the satellites). Radio-frequency engineers, system engineers, and technicians from CSIR SAC were involved in the preliminary design review and technical discussions. Among other projects undertaken by the CSIR’s team was the construction of a new 13-metre full motion Ka-band antenna. The US-designed Spaceway satellite network will provide high-speed, two-way communications for Internet, data, voice, video, and multimedia applications. The spacecraft has approximately five to eight times the capacity of current satellites and features innovative, on-board digital processors, packet switching, and spot beam technology. Spot beam technology will enable the satellite to provide services to small terminals, while on-board routers will enable mesh connectivity. Users of the system will thus be able to communicate directly with any other user of the facility without requiring connection through a central hub. CSIR SAC has provided TT&C support to international satellite operators and launchers for over 40 years. Its location at Hartebeesthoek, north of Johannesburg, makes it an ideal site for the support of satellites launched from Kourou, Vandenberg Air Force Base, Cape Canaveral, and Sea Launch as well as for total lifetime support of geo-stationary satellites over Africa, Europe, and the Middle East. ■ Why is the Ka-band so crucial for the Spaceway programmes? The Spaceway satellite will provide a wideband (10 Mbps) Direct to Home, two-way Internet service. To provide enough bandwidth to service all their customers, the on-board transmitters must operate at the highest possible frequency. ■ Why such frequencies? Considering that South Africa is in the Tropic of Capricorn there’s the possibility of lots of rain. The region’s rainfall patterns were taken into account at the design stage. Rain attenuation is the major technical challenge to this project: it’s why the Americans are using the powerful Boeing 702-type satellite to provide the Safeway service and it’s also the main reason for having a 13-m antenna. If we could have guaranteed clear weather, we would have been able to support the satellite with an antenna as small as 2 m in diameter. ■ Will South African operators (such as Telkom, Sentech, or Transtel) use any of the Spaceway transponders? No. The final position of the two satellites will be over the American continent with their antenna patterns matched to the North American landmass to service the American public. ■ Are there any direct benefits to South Africa of being a TT&C station? Apart from the obvious financial benefit (R28 million facility investment plus support income) from providing this service, CSIR SAC becomes a world expert in TT&C work in the Ka-band. Also, having the facility on our site gives us an advantage when competing for future Ka-band work with other satellite manufacturers out there. For more visit www.csir.co.za * The Ka-band is the name for a higher radio frequency range, which can pack more data using less transmitter power, than is currently used.

Aerial photograph of the CSIR SAC site with all the antennas that earned it the nickname of ‘antenna farm’. Photograph: Courtesy of the CSIR SAC

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Letters Q

Letters to C rossword s note with interest that QUEST carries a regular crossword. Who invented this kind of puzzle, I asked myself, and I looked it up. Your readers might be interested in what I discovered. The first-ever crossword puzzle appeared in the New York World on 21 December 1913 and started a craze. By 1925, crosswords had reached Britain with similar success and, after lively debate in the letters column, even The Times of London began to carry one. The shape came from the word-square, with its repetition in both directions, and the idea of the differentiated verticals and horizontals probably grew out of the ancient Greek acrostic (‘akros’ meaning ‘at the end’; ‘stichos’ meaning ‘line of verse’), a form of riddle used by the sybils or prophetesses for fortune-telling and recorded by Cicero in De Divinatione. In 1913, Arthur Wynne of Liverpool in England, then working for the New York Sunday World, created a diamond-shaped ‘word-hanger’ and called it ‘word-cross’. The subtitle ‘find the missing cross words’ gave rise to the change of

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name to ‘crossword’. The public soon became familiar with the short words in English – animals from Ai to Yak, the river Po, and the language Erse – and the fashion for crosswords brought back many dying technical words, such as the Apse and Nave in a cathedral, and general words such as Aver, Ire, Emit, and Err. The crossword was the new vehicle for wordpower. By 1925, Wynne had sold six puzzles to the UK’s Sunday Express and earned himself the title of Crossword Originator and Constructor on both sides of the Atlantic. There were now about 10 million fans in the USA; schools were using crosswords for their educational value; and psychologists were finding parallel results when they compared crossword ability with IQ test results. Today, virtually all the world’s newspapers carry a crossword and there are millions of regular solvers. Michael Laing, Durban For more, read Michelle Arnot, A History of the Crossword Puzzle (the first edition of which appeared in the 1920s) and try out its samples of famous crossword puzzles. – Editor

We l l d o n e ! t was wonderful to receive another copy of QUEST, and one of such great quality. Congratulations to you on another triumph. Every high school should receive this.

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Mike Wingfield, University of Pretoria At present, the Academy of Science of South Africa sends two copies to each high school in the country that has a science department. We hope that schoolgoers and teachers find it interesting and helpful and we’re encouraged by the support we’re receiving. – Editor

aiting to collect my daughter, I picked up the third issue of QUEST: Science for South Africa, which I’d found in the school library where she was working on a project. Assuming it was a teenage publication filled with trivia, I absent-mindedly paged through it. In no time I was absorbed by

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your well-researched and clearly written articles on current and interesting issues. In particular, I enjoyed the article on tsunamis. It answered so many questions I’d had, but never felt confident enough to ask for fear of appearing ignorant. The sequence of images you included really brought home the devastation caused by such an event. Further on, there was an article entitled “Why bother with physics?” Now I have all the answers I need when my children pose this question to me in future. Thank you, QUEST, for educating not only our children but us mums as well. I’ve completed a copy of the subscription form at the back of the magazine and will mail it off with my payment to make sure I receive future issues. T. Baird, Bryanston

The best letter from a reader published in the next issue will win a Shaeffer pen. Address your letters to The Editor and fax them to (011) 673 3683 or e-mail them to editor.quest@iafrica.com (Please keep letters as short as possible. We reserve the right to edit for length and clarity.)


Q ASSAf News

Expanded programme for ASSAf

(info@twas.org) or download them directly from the web site: www.twas.org

ASSAf has been selected as one of three partners to the US National Academies African Science Academy Development Initiative (see ASSAf News in QUEST 1[2]). We shall be funded to the extent of R1.5 million per annum for some six years to develop science-based advice on health-related issues. The other two African academies selected as partners in this capacity building exercise are the academies of science of Nigeria and Uganda. The initiative will strive to strengthen the capacities of the African academies to provide evidence-based advice to policy makers and the respective nations in the area of health. It will also enhance regional cooperation among African academies. ASSAf will be able to appoint additional staff to undertake the necessary studies.

Post-doctoral fellowship The South African born Nobel laureate, Professor Sydney Brenner (see QUEST 1[3]), has offered US$100 000 of his Nobel prize for a Sydney Brenner fellowship to South African students to be administered by ASSAf. An award of US$20 000 is to be granted once a year, for an initial period of five years, for work in Brenner’s field of specialization. The period may later be extended. The rules for the fellowship are currently being drafted.

Prizes and fellowships Trieste Science Prize TWAS (Third World Academy of Sciences) and Illycaffé have instituted high level prizes to honour distinguished scientists from developing countries. Two prizes, each worth US$50 000, will be awarded annually for two different fields of science. The fields will be rotated annually. For nomination forms, contact the TWAS Secretariat

Lectures Joint lectures with other academies ASSAf has made an agreement with the Royal Society of South Africa (RSSA) to arrange joint lectures in various centres. Professor Robin Crewe (ASSAf President) has discussed this cooperation with Professor Theuns Erasmus (Chairperson of the Suid-Afrikaanse Akademie vir Wetenskap en Kuns [SAAWK]) and SAAWK members will also be invited to the joint ASSAf/RSSA lectures. Lectures on global warming Last March, the Academy invited former South African, Professor George Philander (Princeton University), to present a lecture series around the country on future global warming from a geological perspective.

He highlighted the fact that humanity’s impressive achievements have enabled us to influence and interfere with the processes that make our planet habitable. This has made us custodians of the Earth. To make sensible decisions on behalf of future generations, it helps us to know of the Earth’s past. Human activity, he said, was bringing with it a rise in the atmospheric concentration of carbon dioxide (one of the ‘greenhouse gases’) so rapidly as to pose a threat over the next few decades of conditions that also occurred about three million years ago – including unstable interactions between the ocean and atmosphere (of the type involved in El Niños) and increased climate sensitivity. The question that arises is “Could we eliminate the conditions that favoured our evolution?” Detailed answers are vital for our efforts to anticipate future climate changes, and, to provide them, we need an integration of the different branches of the earth sciences and close collaboration among those who describe past conditions (palaeontologists, anthropologists) and those who use computer models to predict weather and climate. To cope with global warming, as responsible stewards of our remarkable planet, we need some familiarity with the history of the Earth, a rudimentary understanding of how it functions, and an awareness of how our daily activities affect it.

Q Diary of events Natal Museum 237 Loop Street, Pietermaritzburg The museum has officially opened its Portuguese Gallery. Constructed in the form of a wrecked 16th-century vessel, the display is inspired by important South African wrecks on the east coast (such as the São João and the São Bento). With funds from the National Lottery, it has developed the Towns and Trade exhibit, which features the impact of early trade on communities in the African interior, the excitement of wrecks and underwater treasure, and – especially for science and technology education – an audiovisual presentation of difficulties and challenges that Portuguese sailors faced in navigating the oceans in the 1500s and 1600s. The new display, Stories of Human Origins, confronts the questions “Where do we come from? What are our roots?” In other galleries, there are casts of famous dinosaurs and an exhibition of every species of antelope (including rarities such as the bongo, the addax, and the okapi). The acclaimed marine gallery shows the profusion of animals and lifestyles in the seas round South Africa and a dramatic view of an undersea reef with

its inhabitants. The bird galleries are an identification guide for birdwatchers; visitors can also see rare exotics such as the kiwi, kakapo, and the quetzal, and reconstructions of the giant moa and the extinct dodo. Open: Mon–Fri 09:00–16:30; Sat 10:00–16:00; Sun 11:00–15:00 (closed 1 Jan, Good Friday, and 25–26 Dec). Tel. (033) 345 1404.

Maties Science Winter Week in June University of Stellenbosch Specially for Grade 11 and 12 scholars, the Maties Science Winter Week takes place 26–30 June at the University of Stellenbosch. It provides ideal guidance to learners who are interested in a career in the natural sciences. For further details, contact Marietta van den Worm, tel. (021) 808 2684 or e-mail science@sun.ac.za by 10 June.

SAASTA course in science communication From August–December 2005, the South African Agency for Science and Technology Advancement (SAASTA) is piloting a part-time

programme in science communication. Aiming to develop expertise in this important field, it is for people already employed in a science or science policy environment. Apply by 24 June 2005. For details visit www.saasta.ac.za/apsc

Natural Science Museum City Hall, Smith Street, Durban Visit this museum to find out about the Earth, history, and life on Earth past and present. It has the best collection of small mammals and butterflies of KwaZulu-Natal and a superb collection of British moths and Malawian butterflies. Altogether, there are 296 invertebrates, 36 000 birds, and 8 000 mammals, as well as a quarter of a million species of insects. In the KwaZuzulwazi Science Centre, younger visitors can touch, feel, and assemble a variety of exhibits, try out computers, discover the human body, and much more. Open: Mon–Sat 08:30–16:00; Sun and public holidays 11:00–16:00 (closed Good Friday and Christmas Day). For more, phone the Museum Information Desk at (031) 311 2256, or fax (031) 311 2242, or e-mail nsminfo@prcsu.durban.gov.za

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Back page science Q Humble beginnings You wouldn’t recognize some of today’s best known science journals from their baby pictures. Scientific American, for example, which was started in 1848 and run by two former schoolmates aged 22 and 19, published an odd selection of news at first. The launch issue contained an anecdote about “A Sensible Horse”. When unhitched from the cart it had been pulling one day, it wandered off on its own to the blacksmith’s workshop, where it was found to have a shoe missing. Mind you, a pantechnicon that checked its own tyres would probably make the pages of a science journal today too.

This DVD’s the pits What did make it into Scientific American recently (7 February 2005) was the news that researchers are working on ways to put 40 times more data on DVDs. “A conventional DVD encodes 0s and 1s in the form of pits, which are read by a red laser. The pit sizes and red wavelengths limit the capacity of the disks to at most 4.7 gigabytes per layer.” The next step is to use the blue wavelength, which is shorter and so allows more, smaller pits to be etched on the disk. Beyond that advance is the idea of putting more bits into each pit. Peter Török’s team at Imperial College London has produced asymmetric pits “that look different depending on their orientation, like a lopsided crater. Shining laser light onto the pit from different angles produces different reflections and therefore can register additional bits.”

Straight talk ■ “Reality is nothing but a collective hunch.” Comedienne Lily Tomlin. ■ “It has just been discovered that research causes cancer in rats.” Unknown.

Sweet taste of chocolate Wouldn’t you like to be forced to eat only sweets and puddings? Actually, the charm wears off quite

quickly, two astronauts found. Their predecessors at the International Space Station had dipped rather too deep into the food rations, leaving mostly sweet treats for the next shift. Five weeks of this diet were “kind of a challenge”, said US astronaut Leroy Chiao. (From a report in the Sydney Morning Herald, 31 December 2004.)

Baffled scientists ■ “Research is what I’m doing when I don’t know what I’m doing.” Rocket scientist Werner von Braun (1912–1977). ■ “Truth comes out of error more easily than out of confusion.” Philosopher and author Sir Francis Bacon (1561–1626). ■ “Every sentence that I utter must be understood not as an affirmation, but as a question.” Physicist and Nobel laureate Niels Bohr (1885–1962). ■ “An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.” Educator and Nobel laureate Nicholas Murray Butler (1862–1947). ■ “As far as the laws of mathematics refer to reality, they are not certain, and as far as they are certain, they do not refer to reality.” Physicist and Nobel laureate Albert Einstein (1879–1955).

Elephant-speak Researchers need never forget what elephants said about them during field observations: Elephant Voices is a web site that records and decodes the species’ many forms of communication. Knowing what their body language means could be useful in the Kruger National Park when you find the road blocked by tons and tons of unbudging pachyderm. For more, visit www.elephantvoices.org

On-the-ball maths The cover of maths professor Marcus du Sautoy’s book on prime numbers, The Music of the Primes (Fourth Estate, 2003), was illustrated with photos of these numbers in everyday use –

including the number 23 on a football shirt. And that’s what caught the eye of news editors who happened to see the book the day that footballer David Beckham announced he would wear that number for Real Madrid. Du Sautoy was suddenly in demand. “It must have been the first time that advanced mathematics had been discussed on TalkSport radio,” he wrote in the Guardian (October 4 2004). “When I started to look at Real Madrid’s team it was clear they knew about primes being building blocks, because all the key players at Real Madrid play in prime number shirts.” Would that be Fermat in goal?

The naming game Nature does chaos, taxonomists do order. But that doesn’t mean they don’t have fun when they name organisms. A scarab beetle that comes from a particularly large genus was called Cyclocephala nodanotherwon Ratcliffe. There’s also a sea snail named after tennis player Boris Becker by a fan. For a collection of curiosities put together by biologist Mark Isaak, visit http://home.earthlink.net/~misaak/taxonomy.html

Web sites ■ National Public Radio in the US has a weekly show called Science Friday at www.sciencefriday.com ■ Take an online tour of London’s Science Museum at www.sciencemuseum.org.uk

Answers to Crossword (page 45) ACROSS: 4 Amber, 6 Gen, 8 Flexor, 9 Protein, 11 Civil, 14 Leopard, 16 DOS, 18 Moult, 19 Mites, 22 Genomics, 23 Snail, 25 Cells, 27 Baboon, 28 Nile, 29 Nobel, 30 Latent. DOWN: 1 Iffy, 2 Redwing, 3 Fossil, 5 Mars, 6 Gins, 7 Neon, 10 Epidemic, 12 Legume, 13 Dome, 15 Pathogen, 17 Einstein, 20 Species, 21 Baobab, 22 Global, 24 Ibis, 25 Coil, 26 Lobe.

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