5.1 Classification organises our world

Learning intentions

By the end of this topic, you will be able to: • explain the purpose of classification systems and how they are used by scientists.

a

b

Figure 1 a The American magpie Pica hudsonia and b the Australian magpie Cracticus tibicen

Key ideas

• Classification systems help scientists to communicate. • Scientists identify all living things through scientific names. • Carolus Linnaeus developed the modern Linnaean classification system.

Early classification methods Early humans rst classi ed plants by learning which plants were edible and which were poisonous. A new plant or animal discovered by humans was (and still is) studied and put into a group. Some plants were found to help sick people and others were poisonous. Some animals could produce food, such as milk and eggs. Each generation of scientists worked to improve how these groups were classi ed. Common names or scientific names Scientists try to communicate with each other regularly to help with their research. Before the existence of photographs or computers, scientists would have to draw creatures, such as birds, by hand and describe them in as much detail as they could. This was dif cult, and it was easy to make mistakes as the photographs of the American magpie and the Australian magpie show in Figure 1. Both birds looked so

similar that they were given the same common The Linnaean classification system Greek philosopher Aristotle (384–322 BCE) was the rst scientist to start using systems to describe plants and animals. By the 17th century the early classi cation systems used a hierarchy list of names, starting with large general groups (such as plants and animals) and then dividing name, ‘magpie’. However, their scienti c names are different. The name Cracticus tibicen for the Australian magpie means the same to scientists in every country around the world.DRAFT Figure 3 Part of Linnaeus’s classification system

Aristotle (384–322 BCE) sent his students out to gather local samples and stories. He ordered the samples and stories from least important (rocks) to the most important (wild animals, men, kings, fallen angels, angels and God). John Ray (1627–1705) suggested that organisms needed to be observed over the whole of their lifespans.

Figure 2 A timeline of classification Andrea Cesalpino (1519–1603) suggested classifying plants into groups according to their trunks and fruits. Augustus Quirinus Rivinus (1652–1723) and Joseph Pitton de Tournefort (1656–1708) suggested using a hierarchy of names. Each organism had a long Latin name that described the characteristics of each level of the hierarchy.

each group into smaller and smaller groups based on their characteristics. Each organism ended up with a long Latin name that described the characteristics of each level of the hierarchy. Swedish botanist Carolus Linnaeus (1707–1778) tried these classi cation systems but found their descriptions to be too long. He decided that a simpler system was needed. He changed the descriptions to single words and reduced the number of classi cation groups to seven.

Finding new species

There are many living things that are still to be discovered or named. In 2020, seven new species of peacock spiders were identi ed in Australia. These spiders are the same size as a grain of rice. During their courtship dance, they wave their brightly coloured abdomens. Figure 5 Peacock spiders are unique to Australia.

Small groups of scientists are trying to nd undiscovered plants in Brazilian rainforests before they are destroyed by logging and farming. Often the scientists are supported by large pharmaceutical companies from other countries in the hope that it may lead to the discovery of new medications. The antibiotic penicillin was discovered from a type of mould; aspirin comes from a substance in the bark of willow trees. The next painkiller could come from a small fungus in the rainforest or an insect that relies on the fungus for food. Without a name, the new discoveries would be lost and forgotten. Figure 6 The rainforests of Brazil contain many undiscovered plant species. Comprehend 1 Explain why Linnaeus simpli ed the classi cation system used by previous scientists. 2 Explain why it would be dif cult to classify frogs and 5.1 Check your learning DRAFT Figure 4 Carolus Linnaeus tadpoles using the early methods of classi cation.

Apply

3 Propose two reasons why scientists still classify organisms today. 4 The earliest scientists did not have pens or paper.

Describe how they would have passed on the

information they discovered. Discuss the accuracy of this approach (by describing the advantages and disadvantages of using this method). 5 Aristotle was one of the rst scientists to gather information from wide regions. Propose the method he might have used to tell the differences between a horse and a y.

Quiz me Complete the Quiz me to check how well you’ve mastered the learning intentions and to be assigned a worksheet at your level.

Carolus Linnaeus (1707–1778) introduced the Linnaean classi cation system. Thomas Cavalier-Smith (1942–2021) suggested the kingdom Plantae be split into two kingdoms because of differences in their cells.

Carl Woese (1928–2012) suggested that the bacterial kingdom Monera be split into two domains, and the third domain contain all other organisms.