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Animal Behavior


About the Author LIFE WORLD LIBRARY

Niko Tinbergen’s interest in animals began to manifest itself when, as a boy

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in the Netherlands, he kept sticklebacks in an aquarium. As he watched hour

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after hour the activities of these fascinating little fish, he was forming, without

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knowing it, a lifelong habit of close observation of animals in their natural

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surroundings, which would eventually lead him to international eminence in the field of ethology, or animal behavior. Educated in the Netherlands, he received his doctorate at the University of Leyden in 1932 and five years later became associated with the leading behavioral pioneer, Konrad Lorenz. In 1949 he was called to England to organize a department of research in animal behavior at Oxford University. Based there ever since, and now pro-

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fessor of animal behavior, he has not only continued his behavioral studies

THIS FABULOUS CENTURY

but has also trained numerous young research workers and has still found time to travel widely, coordinating the efforts of behavioral scientists in other countries. He is perhaps best known for research into the behavior of sea birds, and he has spent many years studying the habits of gulls in Europe, America, Africa and the Arctic. Some of the insights gained in these studies appeared in The Herring Gull’s World, published in the U.S. in 1960. His other books include The Study of Instinct, BirdLife, Social Behaviour in Animals and Curious Naturalists. Two books for children, Kleewand The Tale of John Stickle, were originally written in letters to his children during two years of internment as a hostage in a German prison camp during World War II. Dr. Tinbergen was elected a Fellow of the Royal Society in 1962.


Animal Behavior LIFE NATURE LIBRARY

By Niko Tinbergen and the Editors of TIME-LIFE BOOKS TIME-LIFE BOOKS NEW YORK


Contents Introduction 1. The Sense Organs: Windows to the World

8

2. Instinct vs. Learning

38

3. An Infant Science

62

4. Stimuli and What They Do

96

5. The Machinery of Behavior

114

6. Finding One’s Way About

136

7. Living Together

148

8. The Evolution of Behavior

156

Bibliography

157

Credits

158

Index

159


TIME-LIFE BOOKS LIFE NATURE LIBRARY EDITOR Maitland A. Edey

EXECUTIVE EDITOR Jerry Korn TEXT DIRECTOR ART DIRECTOR Joani Spadaro CHIEF OF RESEARCH Beatrice T. Dobie PICTURE EDITOR Robert G. Mason Assistant Text Directors: Harold C. Field, Ogden Tanner Assistant Art Director: Arnold C. Holeywell Assistant Chief of Research: Martha T. Goolrick PUBLISHER Rhett Austell Associate Publisher: Walter C. Rohrer Assistant Publisher: Carter Smith General Manager: Joseph C. Hazenut. Business Manager: John D. McSweeney Production Manager: Louis Bronzo Sales Director: Joan D. Manley Promotion Director: Beatrice K. Tolleris Managing Director, International: John A. Millington

EDITOR: Maitland A. Edey Associate Editor: Percy Knauth Assistant to the Editor: John Paul Porter Designer: Aaron Branch Staff Writers: Dale Brown, Timothy Carr, Peter Wood Chief Researcher: Martha T. Goolrick Researchers: Jane Alexander, David Bridge, Doris Bry, Peggy Bushong, Yvonne Chan, Nancy Jacobsen, Nancy C. Newman, Paula Norworth, Carol Phillippe, Maljorie Pickens, Susan Rayfield, Carol lee Rosenblatt, Roxanna Sayre, Nancy Shuker, Iris Unger, John von Hartz. EDITORIAL PRODUCTION Color Director: Robert L. Young CO/JY Staff: Rosa lind Stubenberg, Joan Chambers, Florence Keith. Picture Department: Dolores A. Littles, Susan Boyle Traffic: Arthur A. Goldberger Art Assistants: James D. Smith, Mark A. Binn, John Newcomb The text for this book was written by Niko Tinbergen, the picture essays by the editorial staff. The following individuals and departments of Time Int. were helpful in producing the book: LIFE staff photographers John Domills, Fritzoro, Robert W. Kelley, Nina Leen, Ralph Morse and George Silk ; Editorial Production, Robert W. Boyd Jr. ; Editorial Reference, Peter Draz; Picture Collection, Doris O’Neil ; Photographic Laboratory, George Karas; TIME-LIFE News Service, Richard M. Clurman. ON THE COVER: A honeybee presents a load of pollen to the hive for inspection. Next it will perform its celebrated pollen ancean intricate series of movements that will explain to the other bees where to find pollen themselves. © 1965 Time Inc. All rights reserved. Reprinted 1969. Published simultaneously in Canada. Library of Congress catalogue card number 65-1 3829. School and library distribution by Silver Burdett Company, Morristown, New Jersey.


Rationale When redesigning the Time Life book, Animal Behavior, I was faced with the difficult challenge of how to visually depict an intangible subject: that of behavior. Behavior covers a broad range of topics from physiology, anatomy, and sociology therefore finding the correct balance between imagery and typography was a struggle. After researching a number of books on animals and behavior in general, I found that most follow a typical textbook style which can bore a reader quite quickly. For the redesign of this book I chose to focus on using a graphic treatment of images as a way of expressing the spontaneous nature of animals. This technique allowed me to break free from the norm of book design. My choice of type being Trade Gothic and Kepler was simple so as to not create a conflict between image and type. I felt the imagery needed to lead the path for expression and should not be contained by boxes and boundaries. The images should reflect the freedom that animals experience in the wild. I used splatters and scratches based roughly on the Rorschach test to link behavioral studies and exotic animal together into one unified element.


8


1

The Sense Organs

To b e e ffi c ie nt , th e b e h av io r o f a n im a ls m u st in c lu d e th e abilit y to d o th e rig ht th in g s in the rig ht c irc u m sta nc e s. In other w ord s, u n le ss a n im a ls c a rry ou t the c om p lic ate d m o v em ents w e c a ll b eh av ior at the rig ht m om ent a nd in the rig ht p lac e , the se w ill b e ineffe c tiv e . In ord er to d o th is, ho w e v er, the y m u st h av e in form ation ab out c ond ition s in the outsid e w orld . T h is in form ation re ac he s them th rou g h their sen se orga n s. S en sor y stim u lation is often the st a rtin g p oint of b e h av ior: a d o g se e s its m a ster p u t on h is h at a nd im m e d iate ly b a rk s in a ntic ip ation of a w a lk , a nd onc e ou tsid e st a rts ru n n in g in p u rsu it o f a sc e nt . T hu s h e re ac t s t o h is e n v iro n m e nt a n d o u r st u d y o f the w ay b eh av ior is c ontro lle d in a n im a ls c a n therefore lo g ic a lly sta rt w ith a st u d y of the ou tsid e stim u li to w h ic h the y c a n re sp ond . W h at sort of stim u li d o a n im a ls re c eiv e ? F irst of a ll, the y a re not ne c e ssa rily th e sa m e a s th o se to w h ic h a hu m a n m ig ht re ac t . Fa ilu re to ap p re c iate th is c a n le ad to fa lse c onc lu sion s. I onc e he a rd of a go v ern m ent offic ia l w ho sp ent $ 5 ,0 0 0 on m oth b a lls to k e e p bird s off the ru nw ay s of a n a irp ort w here th e y c o llid e d w ith je t p la n e s . W h at h e d id n ot k n o w w a s th at bird s h av e a very p o orly d e velop e d sen se of sm ell- the m othba lls b othere d them not at a ll.

9


The Sense Organs

T h e fac t o f t h e m at t e r is t h at d iffe re nt a n im a ls , in c lu d in g m a n , h av e d ifferent “w ind o w s to the w orld .” S om e h av e sen sor y e q u ip m ent th at in som e re sp e c ts is m uch p o orer th a n ou rs ; in others, the sen se s a re fa r su p erior. T here a re e ven a n im a ls th at reac t to stim u li w h ic h w e c a n not d e te c t at a ll-sig hts or sou nd s or sm e lls w h ic h w e c ou ld not d isc o v er w ithou t a rtific ia l e x ten sion s to ou r o w n sen se orga n s. B e e s, a s w e k now, se e a nd reac t to u ltrav iolet lig ht , w herea s w e hu m a n bein gs h ave to tra n sform the u ltrav iolet ray s w ith sp ec ia l ap p a rat u s into the k ind of lig ht th at w e c a n se e . O nc e it w a s re a liz e d th at a n im a ls m ig ht h ave sen se orga n s q u ite d ifferent from ou r o w n , it b e c a m e im p erativ e to e x p lore their sen sitiv it y to o u tsid e , stim u li sy stem atic a lly a nd thorou g h ly. T h is is a lab oriou s ta sk , but , lik e a ll e x p loration , it is e x trem e ly fa sc in atin g a nd re w a rd in g . A nd the fi rst ste p in su c h a st u d y is to fi nd ou t e x ac tly ju st w h at it is in a g iv en sit u ation th at a n a n im a l is re sp ond in g to . K a rl Vo n F risc h , th e fa m o u s A u st ria n z o o lo g ist , gav e . T h is fi e ld of re se a rc h its in itia l im p e t u s. H is n a m e is rig htly c on ne c te d w ith h is w ork on b e e s , bu t he a nd h is nu m erou s p u p ils h av e a lso d one ou tsta nd in g re se a rc h on the sen se s of other a n im a ls, p a rtic u la rly on h e a rin g in fi sh e s . O n e o f v on F risc h ’s e a rly p ap e rs w a s sim p ly c a lle d “A F ish T h at C om e s W hen O ne W h istle s”a nd ind e e d he h ad tra ine d a fi sh to d o ju st th at . H ow e v er, th is w a s on ly the b eg in n in g ; von Frisch a lso w anted to k now w hy the fi sh c am e w hen he w h istled , a nd h is line of re a son in g illu strate s b e autifu lly the re se a rc h w h ic h st u d ie s of a n im a ls’ sen se s m u st p u rsu e .

10


W h at stim u late d the fi sh to c om e to the su rfac e w hen the w h istle w a s blo w n ? B e c au se w e c a n h e a r, w e m ig ht a ssu m e th at th e fi sh c ou ld hea r to o, a nd th at it w as re sp ond in g to the sou nd . But the fi sh m ig ht not b e able to he a r-it m ig ht h av e ju st se en the m o v e m ents o f th e m a n w ith th e w h ist le a n d re sp o n d e d to th e se . H o w is o n e to k n o w ? O n e w ay is to m a k e th e sa m e m o v e m ents , bu t w ith o u t w h istlin g. If the fi sh do e s not c om e , c lea rly it is not m ovem ent a lone th at stim u late s it . C onversely, one c a n w h istle w ithout m ov in g a nd se e w he ther the fi sh re sp ond s. O r one c a n blo c k off or rem o v e the sen se orga n th at is thou g ht to b e re sp on sible for the fi sh ’s b eh av ior, in th is c a se the in ner e a r: if it fa ils to c om e no w it m ay b e a ssu m e d th at it c o u ld h e a r p re v io u sly. O n c e it is e st ab lish e d th at th e fi sh c a n he a r, one c a n p ro c e e d to e x p lore sy stem atic a lly w h at e x ac tly it s h e a rin g o rga n c a n ac h ie v e -h o w ac c u rat e ly it c a n d ist in g u ish b e t w e e n d iffe re nt le v e ls o f p it c h o r h o w w e a k t h e so u n d c a n b e m ad e b efore the a n im a l fa ils to re ac t . A ny re sp on se w h ic h a n a n im a l m a k e s n at u ra lly-su c h a s c o m in g for fo o d–c a n b e u se d a s a n ind ic ator of b e h av ior. H o w e v er, th e se n at u ra l re sp on se s a re not a lw ay s c onv en ient to w ork w ith a nd not a lw ay s a s c lea r-c ut a s a n inv e stigator w ou ld lik e . T herefore he m ay d e c id e t o c o n d it io n o r t ra in a n a n im a l t o a sp e c ifi c st im u lu s b y p re sentin g th at stim u lu s re p e ate d ly to ge th er w ith a n at u ra l one . T h at is w h at von F risch w as doin g w hen he w h istled every tim e th at he offere d fo o d to the fi sh . A nother w ay of c ond ition in g is to fl a sh a lig ht e v e r y tim e on e fe e d s a n a n im a l, so th at it a sso c iate s lig ht a n d fo o d . If it c a n se e at a ll, so on e r or late r it w ill re sp on d to th e lig ht a lone in e x p e c tation th at fo o d w ill b e p re sent . T h is tra in in g m e tho d , a s w e sh a ll se e , is w id e ly u se d . Phy siolo g ists lik e to ap p ly still a nother m e tho d of inv e stigation in h ig her a n im a ls : re g isterin g the re sp on se to a stim u lu s d ire c tly b y ele c tric a l m ea n s. T he c ore of each sen se orga n is form e d by sen sory c e lls , w h ic h a re th e re a l re c e iv e rs o f th e st im u lu s . S u c h c e lls a re c on n e c te d b y th in n e r v e fi b e rs w ith th e c e nt ra l n e r v o u s sy ste m . T he se nerv e fi b ers a re the c om m u n ic ation line s w h ic h tra n sm it , in rap id se q u enc e to the bra in , v o lle y s of c hem o -e le c tric a l im p u lse s. T he se im p u lse s, e ac h la stin g a thou sa ndth of a se c ond , reg ister on d e lic at e in st ru m e nt s a s “ac t io n p o t e nt ia ls .” A n y c o rre sp o n d in g v a riation in th e ir fi rin g p at te rn in d ic ate s th at th e se n se orga n is re sp ond in g to the stim u lu s. T hu s, a lig ht fl a she d into the e y e p ro duc e s ch a n ge s in the ac tion p otentia ls in the op tic nerve , a nd the se 11

No Reaction to Sound Von Frisch whistled every time that he offered food to the fish and yet no response. So another way of conditioning a fish is to flash a light every time he feeds the animal, so that it associates light and food.


The Sense Organs

w ill reg ister on a sen sitiv e m eter. H ow e v er, th is m e tho d of re se a rc h a lso h a s its lim it ation s, a s has the tra in in g m etho d . For va riou s reason s the ac tion p otentia ls a nd beh av ior do not inva riably te ll the sa m e story of sen sory c ap abilit y, so the fu nc tion s of sen se orga n s a re b e st stu d ie d w ith b oth m e tho d s. A short re v ie w w ill show the a m a z in g v a riet y of sen sory abilitie s w e fi nd a m on g a n im a ls. L et u s b e g in b y c on sid erin g the abilit y to se e . V ision , or resp on siveness to lig ht, is one of the five basic se n se s o f t h e a n im a l k in gd o m . H o w e v e r, n o t a ll a n im a ls se e th e sa m e th in g s. For in st a nc e , th e y a re n ot a ll sen sitiv e to th e sa m e ra n ge of the sp e c tru m . W e h av e a lread y note d th at b e e s a n d m a ny o th e r in se c t s m ay b e se n sit iv e to a w id e ra n ge of u ltrav io le t lig ht , bu t the y a re fa r le ss sen sitiv e to re d-in fac t , m o st lig ht th at w e se e a s re d is inv isible to them . B u t w h at a b o u t re d fl o w e rs t h at a re so o b v io u s ly at t rac t iv e t o in s e c t s ? A c t u a lly, a s v o n F risc h h a s p ointe d ou t , fe w flo w ers p o llin ate d b y-a nd there fore ad ap te d to -in se c ts a re re a lly re d ; tho se th at ap p ea r re d or pu rple to u s refle c t a g reat dea l of blue as w ell, a nd it is the blue th at th e in se c ts se e . O r c on sid er th at p o p u la r w ild flow er, the E u rop e a n p op p y. W e se e it a s brig ht sc a rle t , bu t w e a lso o b ser v e th at it is v isite d b y b e e s a nd other in se c ts. A sim p le te st w ill sho w th at the p o p p y re fle c ts u ltrav io le t lig ht w h ic h the se in se c ts se e . W e w ill pic k t w o p op pie s a nd flatten them out on a boa rd in a field w here p op p ie s g ro w . O n e is c o v e re d w it h a fi lt e r w h ic h absorbs a ll v isible lig ht but tra n sm its u ltrav iolet. T he other flow er is c overe d w ith t w o fi lters-one w h ic h ab sorb s a ll u lt rav io le t lig ht p lu s a fi lter w h ich absorbs a ll v isible lig ht. B oth flow ers now ap p e a r id entic a lly blac k-th at is, inv isible to ou r e y e s-bu t the in se c ts w ill u n he sit atin g ly a lig ht 12

on the fi rst flow er, re sp ond in g to the refle c tion of the u ltrav iolet ray s.M a ny other flow ers, such a s tho se of the c om m on c inq u efoil, re fle c t u lt rav io le t to o . T h e se blo ssom s lo o k u n iform ly ye llow to u s, but the y re fle c t a lot of u ltrav iole t as w ell. H ow ever, each p eta l has a la rge p atch at its b a se w h ic h d o e s not re fle c t u ltrav iole t , a nd so m u st ap p e a r d iffe re nt-c e rt a in ly d a rk e r-t o the b e e s th a n the re st of the flo w er. A nother intere stin g q u e stion ab ou t the v ision of a n im a ls is w hether the y ac tu a lly d istin g u ish c o lors w ith in the sp e c tru m v isible to them or w hether they reac t on ly to d ifferenc es in brig htne ss. T h is c a n b e te ste d in the sa m e w ay th at hu m a n b ein g s a re te ste d for c o lor v ision-w ith the d ifferenc e th at a n im a ls h av e to b e tra ine d in som e w ay to let u s k now w hat they see. A ga in w e u se the sam e tech n ique that von F risch u sed in gettin g a fi sh to re sp ond to a w h istle , but th is tim e w e intro d u c e c o lors a s stim u li in ste ad of so u nd s. Su p p o se , for in st a nc e , w e tra in a te st a n im a l to a sso c iate fo o d w ith a re d tria n g le by sho w in g it su c h a tria n g le e v er y tim e w e offer it fo o d . O nc e it h a s lea rne d th is, w e then show it other tria n g le s th at a re id entic a l e xc e p t th at the y a re blue , g re en , pu rple - m a ny c olors, a lon g w ith se v era l sh ad e s of g ray. If th e a n im a l still re ac t s t o t h e re d t ria n g le , o r t o a c o lo r c lo se t o re d , lik e p u r p le , c a n w e t h e n a ssu m e t h at it s e e s c o lo r? Ye s , w e c a n -a lm o st . T h e re is a c h a n c e t h at t h e a n im a l is c o lo r b lin d a n d is “fa k in g � c o lor v ision b y re c o g n iz in g the c o lor as a c erta in sh ade of g ray. S o w e m a k e a te st for it s abilit y to d isc rim in ate b e t w e en g ray s . W e t ra in t h e a n im a l t o a sso c iat e fo o d w it h o n ly o n e p a r t ic u la r sh ad e o f g ray, t h e n p re se nt it w ith a w ho le ra n ge of g ray s of v a r y in g sh ad e s. If it re sp ond s to m a ny g ray s rather th a n to the p a rt ic u la r o n e it w a s t ra in e d to , th e n w e c a n


What about red flowers that are so obviously attractive to insects? Actually, as von Frisch has pointed out, few flowers pollinated by-and therefore adapted to-insects are really red; those that appear red or purple to us reflect a great deal of blue as well, and it is the blue that the insects see.

13


The Sense Organs

a ssu m e t h at it s b rig ht n e ss d isc rim in at io n is n o t v e r y ac c u rat e , a nd th at its in itia l re sp on se in the c olor te st w a s ind e e d a re ac tion Infrared is a form of heat, and certain to c o lor a lone . O f c ou rse w e m u st m a k e su re th at the a n im a l c a ncreatures, notably the rattlesnake and its not se e either u ltrav io le t or in fra re d lig ht , w h ic h som e of ou r te st relatives, have organs that detect it as ef- o bje c ts m ig ht g iv e off. fectively as though they “saw” it in our N o a n im a l h a s y e t b e e n d isc o v e re d th at c a n “se e ” in fra re d lig ht sense of the word. In front of and slightly w ith it s e y e s , bu t th ere a re oth er w ay s of “se ein g ” th a n w ith e y e s below their eyes, a lone . In fra re d is a form of he at , a nd c erta in c re at u re s, notably the rattle sn a ke a nd its relative s, h ave orga n s th at dete c t it as effe c tively a s th o u g h th e y “ saw ” it in o u r se n se o f th e w o rd . In fro nt o f a n d slig htly b e lo w their e y e s, the y h av e t w o p its w h ic h c onta in ~ th in m em bra ne , b eh ind w h ic h is a c av it y fi lle d w ith a ir. T he m em bra ne is ric h in ner v e end in g s-there a re 3 ,5 0 0 in e ac h p it , on a su rfac e of th re e to fou r sq u a re m illim e ters, w h ic h is ab ou t 10 0 ,0 0 0 tim e s a s m a ny a s hu m a n s h ave on a n e q u a l a rea of sk in . F u rtherm ore , the se n e r v e e n d in g s a re v e r y c lo se to th e su rfac e o f th e m e m bra n e , so th at a ll in a ll a pit v ip er, a s suc h sn a k e s a re c a lle d , c a n sen se from a fo ot a nd a h a lf aw ay a t u m bler of w ater on ly a fe w d eg re e s w a rm er th a n the su rrou nd in g a ir. R at tle sn a k e s w ill ac t u a lly strik e at su c h

Sight by Heat?

14


o bje c t s , w h ic h m a k e s it se e m lik e ly th at th e y u se th is sen sitiv ity to lo c ate w a rm -blo o ded prey. A nd not on ly do these organ s resp ond to rad iant he at bu t the fac t th at the y a re su n k in pits a nd h av e so m a n y n e r v e e n d in g s a lso e n ab le s th e sn a k e s to d e te c t the d ire c tion from w h ic h the he at c om e s. T he rim s of the pits ac t a s sc re en s for rad iation ; from the sid e s ; the y c a st sh ad ow s w h ic h o f c o u rse v a r y w ith th e d ire c tion fro m w h ic h the he at re ac he s the p its. T he se in form the sna kes about the d irec tion of the heat sou rce a nd en able them to strik e w ith g re at ac c u rac y. A nother p oint of intere st in v ision is the e x tent t o w h ic h a n a n im a l c a n d e t e c t d e t a ils in it s v isu a l fie ld . T h is is b y no m e a n s a u n iv ersa l ac c om p lish m ent : m a ny w orm s a nd she llfi sh , for in st a n c e , h av e w h at is c a lle d a “ d iff u se lig ht se n se � in t h e ir sk in s— t h e y se e lig ht o n ly t h e w ay w e fe e l w a rm th . A ll the y c a n rea lly d o is to notic e w he ther it is d a rk or lig ht ; the y h av e at b e st on ly v er y p o or m e a n s of d e te c tin g w here the lig ht c om e s from , le t a lone se ein g o bje c ts. H ig h e r a n im a ls , b y c o nt ra st , h av e d e v e lo p e d e y e s w h ic h c onta in a n o p tic a l ap p a rat u s. Verte brate s u se a len s w h ic h p roje c ts a n im a ge on a re t in a m ad e u p o f m illio n s o f se n so r y c e lls , e ac h o f w h ic h c o n t rib u t e s a t in y p a r t t o t h e tot a l v isu a l im a ge . In se c t s a n d th e ir re lativ e s h av e c om p ou nd e y e s-the se h av e no len se s bu t a re m ade up of a nu m ber of c on ic a l tu be s c a lled o m m at id ia , w h ic h d iv e rge o u t w a rd fro m t h e o p tic nerv e to g iv e the in se c t a w id e fie ld of v ision . E ac h om m atid iu m is in su late d o p tic a lly from its neig hbors by a m a ntle of pig m ent , each p rov id e s m ere ly one p oint of the v isu a l im a ge , a nd a ll the se p oints or d ots fit to ge ther to p ro v id e a m o sa ic lik e p ic t u re . V isu a l ac u it y, or the abilit y to d istin g u ish d e t a ils , is m u c h g re at e r in e y e s e q u ip p e d w it h le n se s t h a n it is in t h e c o m p o u n d e y e s o f in se c ts. For a b e e , t w o d ots slig htly le ss th a n one d e g re e of a rc ap a rt w ill m erge to ge th er in d is-

tin g u ish ably into one , but hu m a n s, u nder favorable c irc u m st a n c e s , c a n d istin g u ish b e t w e en d ots on ly som e 4 0 se c ond s of a rc ap a rt , or one n inetieth of one deg ree , a nd m a ny bird s seem to d o e v en b e t ter. G re at v isu a l ac u it y h a s , o f c o u rs e , m a n y ad v a n t a g e s . It a llo w s p re d at o r y a n im a ls t o se e t h e ir p re y f ro m v e r y fa r aw ay : in s e c t -e at in g fa lc o n s a re a b le t o se e in d iv id u a l d ra go n fl ie s a h a lf a m ile d ist a nt , w h e re a s for u s th e sa m e in se c t b e c om e s ind istin g u ish able at ab out 10 0 ya rd s. By the sa m e tok en , m a ny v u lnerable a n im a ls c a n se e th e ir p re d ato rs fro m a fa r. G o o d v isio n is g e n e ra lly im p o r t a n t in m a n y o t h e r w ay s a lso , of c o u rse . W e sh a ll se e later, for e xa m p le , th at m a n y bird s a re ab le t o re c o g n iz e their p a rtners, their flo c k m ate s or their y ou n g a s ind iv id u a ls, a nd in m a ny c a se s th is is c lea rly a m at t e r o f th e ir re c o g n iz in g th e se o th e rs o f their sp e c ie s b y sig ht . P ro bin g still d e e p er into the q u a litie s of v ision , w e fi nd th at m u c h m ore is inv o lv e d th a n m ere d istin c tion o f q u a lit y or q u a ntit y o f lig ht a n d d isc rim in ation b e t w e en o bje c ts. W h at , for e xa m p le , ab ou t m o v in g o bje c ts? T h is is a n intere stin g thou g ht : to the e lem ent of d isc ern m ent it ad d s t h e e le m e nt o f t im e . It m e a n s t h at a n a n im a l m u st b e able to re g ister d ifferenc e s in t h e m o m e n t o f st im u lat io n b e t w e e n c e lls o r g ro u p s o f c e lls in t h e re t in a . A m o v ie fi lm is a g o o d illu st rat io n o f t h e p ro b le m . W e k n o w th at th e p ic t u re s w e se e on th e sc re e n d o n ot re a lly m o v e bu t c on sist of a serie s of d ifferent st ill im a g e s , e ac h o f w h ic h fa lls o n a slig h t ly d iffe re nt sp o t o n o u r re t in a th a n it s im m e d iat e p re d e c e sso r. T h e illu sio n o f m o v e m e nt is p ro d u c e d b e c au se o n e e le m e n t o f t h e re t in a is able to c onv e y in form ation of the e x ac t m o m ent it w a s stim u late d to oth er c e lls th at a re then stim u late d in t u rn . T hu s a c on sta nt flo w of in form ation a nd stim u lation is se t u p w h ic h in its su m ad d s u p to a p ic t u re of m o v em ent . 15


The Sense Organs

To b e able to d o th is, it is c le a r th at there m u st be cro ss-con nec tion s bet w een the sen sory cellsa nd inde e d , such c ro ss-c on ne c tion s a re pre sent in enorm ou s profu sion . In in sec ts they a re fou nd in the ga n g lia , or ner v e c enters, th at lie im m e d iate ly b e h in d th e e y e . In h ig h er a n im a ls , n ot on ly a re the nerv e c e lls im m e d iate ly in front of the sen sory c e lls interc on ne c te d but a lso other cells that lie deep er dow n in the nervou s sy stem . B ut there is e v en m ore to m ov em ent th a n th at : w h at a b o u t sp e e d o f m o v e m e nt? C le a rly th is is im p o rt a nt-a n d in d e e d a n im a ls at t im e s d o re ac t d ifferently to o bje c ts th at m ov e at d ifferent sp e e d s. O ften th e y c a n e v en d isc rim in ate b et w e en a sm o oth m ov em ent a nd a w av y or a n irreg u la r one . H ow the nervou s sy stem ach ieves th is, ho w e v er, is a s y e t u n k no w n . A nother c om plex asp e c t of v ision is the d istinc tion a nd recog n ition of shap es. It is qu ite easy to tra in a bird or a m a m m a l to re sp ond to a c irc le a n d t o ig n o re a re c t a n g le T h e fe m a le d ig g e r w a sp , w ho sto c k s her bu rro w w ith in se c ts she h a s k ille d a s fo o d for her la rv ae , c lea rly h a s th is abilit y. T he q u e stion is , ho w d o e s she m a n a ge to fi nd her w ay bac k from som e d ista nt hu ntin g g rou nd to her o w n bu rro w in a la rge c o lony ? I soon fou nd that these w asp s rem em bered the arra n gem ent of sm a ll la nd m a rk s such a s p ebble s, pine c one s a nd t u fts of g ra ss a rou nd their bu rrow s. K now in g th is, I tra ined w asp s to recog n iz e a c irc le o f p in e c o n e s w h ic h I la id o u t a ro u n d the entra nc e . W hen such a w a sp w ent forag in g , I m o v e d th is c irc le a fo ot or so . T he re su lt w a s th at w hen she retu rne d , she sea rche d v a in ly for h e r bu rro w in th e c e nt e r o f th e rin g o f c o n e s , ig norin g th e re a l ent ra nc e w h ic h w a s in p la in v ie w. In su b se q u ent te sts, I offere d her a c hoic e b e t w e en a c irc le of d a rk stone s a nd a tria n g le or a n e llip se of pine c one s. A lthou g h she c ou ld d istin g u ish the stone s from the c one s p erfe c tly w ell, a s I k ne w from other te sts, she w ent to the stone c irc le -ju st b e c au se it w a s a c irc le . 16

T h is sa m e m at ter of form d isc rim in ation h a s b e e n st u d ie d in t e n se ly in a v e r y in t e re st in g e x p erim enta l a n im a l, the ¡o c topu s. L ik e a ll the c epha lop o d s, the o c topu s has h ig h ly develop ed e y e s, in m a ny re sp e c ts sim ila r to the len s e y e s o f v e rte brate s . It d ist in g u ish e s w e ll b e t w e e n sh ap e s a nd c a n e a sily b e tra ine d to c om e forw a rd , p re p a rin g to fe e d , w hen sp e c ific sh ap e s a re sho w n . It h a s no d iffic u lt y in te llin g a v ertic a l from a horiz ont a l re c t a n g le . H o w e v er, it gets con fu sed w hen presented w ith t w o oblique rec ta n g les, one held at rig ht a n g les to the other, or w ith a V-lik e a nd a W -lik e fi g u re . It lo ok s a s if in sh ap e re c o g n ition a p ro c e ss is inv olv e d in w h ic h the v ertic a l a nd horiz onta l p roje c tion s of th e d ifferent sh ap e s a re c om p a re d to e ac h other-a s if som e k ind of c entra l ner v ou s sc a nn in g of the re tin a ta k e s p lac e .

Touch and other Senses S en se orga n s that resp ond to touch : to pressu re or to other m ech a n ic a l ac tion a re a n im p orta nt p a rt o f th e b a sic se n so r y e q u ip m e nt o f m o st m a m m a ls. In their sim p le st form s, the y o c c u r in the sk in , w here the y a re o b v iou sly u sefu l in m a inta in in g a c lo se c ontac t w ith the su rrou ndin g e n v iro n m e nt . B u t m e c h a n ic a l st im u li o f other k ind s a re u se d for m a ny other, fa r m ore sp e c ia liz e d p u rp o se s. B y the ten sion of som e m u sc le s, b y the la x ne ss of others, b y the p o sition of h is b one s, tend on s a nd joints, a hu m a n b e in g ge t s a c o n st a nt st re a m o f e n o rm o u sly d eta ile d a nd u sefu l in form ation ab out h is p o stu re a nd h is m ov em ents-a s is the c a se w ith a ll h ig h e r a n im a ls , w h ic h h av e h ig h ly c o m p le x s e n s e o rg a n s in t h e ir m u s c le s , t e n d o n s a n d jo int s . In se c t s , w h ic h h av e a n e x t e rn a l sk e le to n , h av e o th e r a rra n ge m e nt s fo r th e sa m e ’ p u rp o se s. Pad s of sen sor y h a irs a nd g rou p s of m inute dom e -sh ap ed orga n s a re often fou nd at the joint of a leg seg m ent. In the norm a l p osition the se h a irs to u c h the ne x t se g m ent in su c h a


w ay that any bend in g of the joint w ill m ove or bend the ha irs slig htly, t rig ge rin g a re sp on se in th e sen sor y n e r v e s .T h e orga n s sen sitiv e to tou c h re p ort m e c h a n ic a l stre sse s d u e to g rav it y on the in se c t ’s b o d y a nd a llo w it to p erc eiv e its o w n w eig ht , or e v en th at of a lo ad w hen it sta nd s, a nd to fe el w hen it h a n g s u p sid e dow n . W eb spid ers u se th is sa m e abilit y, but w ith a d ifferent m e c h a n ism , to lo c ate a n in se c t c au g ht in th eir w e b : p u llin g w ith th eir le g s at th e st ra nd s , the y c a n fe e l the d ire c tion w h ic h offers the m o st re sista nc e . S t ay in g rig ht sid e u p in t h e ir w o rld is a p ro b le m c o m m o n t o a ll a n im a ls, a nd here , to o , the sen se of tou c h a nd pre ssu re is inv olv e d . In gen iou s m o d ific ation s of the touch orga n s a re u se d to d eterm ine the d ire c tion of g rav it y. In v ertebrate s, th is is ac c om p lishe d by one or m ore tiny, h a rd , p e b ble lik e b o d ie s, c a lle d oto lith s, in the in ner e a r. H e av ie r t h a n t h e su rro u n d in g t issu e , t h e o t o lit h s re st o n a c u sh ion of sen sor y h a irs, to w h ic h the y a re at t ac he d b y a lay er of m u c ou s. W hen the a n im a l is tilte d the h a irs a re b ent in one d ire c tion or a nother, a nd th is ac ts a s the stim u lu s. In m a ny c ru stac ea n s the otolith is not form e d by the a n im a l itse lf but c on sists of a g ra in o f sa n d th at th e a n im a l p ic k s u p a n d in se rt s e v e r y t im e it sh e d s its she ll. A lois K reid !, a re sou rc efu l A u stria n z o o lo g ist of the 19 th C entu ry, d em on strate d the fu nc tion of th is g ra in of sa nd in a m o st in gen iou s a nd intere stin g fa sh ion . H e put a sh rim p in a n aq u a riu m on a b e d of iron fi lin g s in ste ad of sa nd . W hen it m olte d , the u n fort u n ate a n im a l end e d w ith a g ra in of iron in its g rav it y orga n , a nd w hen a stron g m a g ne t w a s - he ld o v er it , it sw a m u p sid e d o w n .

Swimming Upside Down He put a shrimp in an aquarium on a bed of iron filings instead of sand. When it molted, the unfortunate animal ended with a grain of iron in its gravity organ, and when a strong magnet was held over it, it swam

S om e aqu atic in se c ts ke e p their ba la nc e in the w ater in still a nother upside down. w ay. T he y c a rr y ne x t to their b o d ie s a sm a ll su p p ly of a ir, he ld in p lac e b y a c o at o f w ate r-re p e lle nt h a irs . T h e sp ac e s b e t w e e n th e h a irs a re not la rge enou g h to le t the a ir e sc ap e , but the y d o p erm it d ire c t c ontac t b e t w e en the a ir bu bble a nd the su rrou nd in g w ater. W ith a n “a ir p o c ket � like th is on each side of its bo d y, such a n in se c t c a n te ll if one sid e is tip p e d d o w n , b e c au se the sid e th at is d e e p er in the w ater w ill b e su bje c te d to a v ery slig htly inc re a se d p re ssu re . T h is c om pre sse s the a ir in the bu bble , p erm ittin g the w ater to pre ss slig htly fa rther into the p o c k et ; sen sitive h a irs d ete c t th is a nd relay the in form ation to the in se c t th at it is no lon ger horiz onta l. In se c ts a lso de p end on sen sory h a irs for other k ind s of in form ation-pic k in g u p m inu te v ibration s in the w ater, for e x a m p le . A w ater bu g , N o t o n e c t a , fi n d s it s p re y t h is w ay. H a n g in g u p sid e d o w n fro m t h e su rfac e , it u se s the h a irs on its lon g , d e lic ate le g s to d e te c t rip p le s sent ou t b y other tiny sw im m ers or stru g g lin g in se c ts w h ic h h av e fa llen into the w ater. In a n aq u a riu m , N otone c ta c a n b e stim u late d 17


The Sense Organs

to sw im to w a rd a th in w ire h e ld on th e w ate r su rfac e a n d v ib rat e d ge nt ly so a s t o se n d o u t little rip ple s. It is a m a z in g how ac c u rately the se in se c ts c a n a im for the sou rc e of the rip p le s b y th is se e m in g ly p rim itiv e m o d e of orient ation , a nd th is w ithou t the a id of a ny v isu a l g u id e . T he w h irlig ig b e etle s h av e gone N otone c ta one b etter. T he y a re su rfac e sw im m ers, a nd a s the y g lid e ab out on p ond s the y re st their fe e lers ju st on top of the w ater. T he se fe e lers a re e q u ip p e d w ith p ad s of sen sory ha irs w h ich detec t not on ly su rfac e rip p le s m ad e b y oth er m o v in g in se c ts b u t e v e n t h e p re s e n c e o f m o t io n le s s o b je c t s su c h a s ro c k s or flo atin g p ie c e s of w o o d n e a rb y-the w ater bu g ap p a rently h a s the abilit y to reg ister the e c ho e s of its o w n rip p le s b ou nc in g off the se o b stac le s.

Echo Location T he p rinc ip le of e c ho lo c ation is c a rrie d to e xtraord in a ry len g th s by the fi ne st sp ec ia liz ation s of the m e c h a n ic a l sen se s w e k no w : the orga n s of hea rin g . H ea rin g itse lf is a lread y a ston ish in g enou g h , a nd it m ay be ap propriate to p au se here fo r a fe w w o rd s a b o u t it . W h at w e re c o g n iz e a s “so u nd ” is ac t u a lly the c re ation of p re ssu re w av e s in a m e d iu m lik e a ir o r w at e r b y so m e k in d o f m o v e m e nt . If a t u n in g fo rk is st r u c k , it s en d s w ill v ibrate a n d th is v ibration a ffe c t s th e su rro u n d in g a ir, sen d in g rap id ly a ltern atin g w av e s of h ig h a nd low pre ssu re out into the room . W hen these w aves h it a m em brane like an e a rd ru m , it w ill v ibrate a lso , a nd the se sig n a ls, sent to the bra in , a re re c og n iz e d as sou nd s. T he d iap h ra g m in a te le p h on e re c e iv e r is sim p ly a v ibrator, send in g sou nd w av e s to ou r ea rs ; so is a rad io lou d sp e a k er. N ot a ll e a rs a re m e m bra n e s. M o sq u ito e s h e a r w ith p lu m e s on th eir a nten n ae . M a ny lo c u st s h ave” ea rd ru m s” on their legs ; no c tu rn a l m oth s often h av e them on the sid e s of their b o d ie s. In genera l, in se c t e a rs a re fa r le ss e lab orate th a n 18

the ea rs of vertebrate s ; for one th in g , the y se em u n able to d istin g u ish p itc h . Ye t the y a re v er y sen sitiv e to d ifferenc e s in sou nd inten sit y, a nd the y utiliz e to the fu ll the rhy th m ic prop ertie s of sou nd p u lse s. T he m a le s of the g ra sshop p er E p h ip p iger p erform a rhy th m ic stac c ato son g to attrac t fem a les : th is son g c a n be suc c essfu lly im itate d w ith sou nd s of a ny pitc h w ith in their ra n ge of he a rin g , bu t on ly w hen the se sou nd s either b e g in or end abru p tly. A tap e re c ord in g o f a lo n g , sm o o th w h ist le e lic it s n o re sp o n se w h ate v e r fro m th e fe m a le s , bu t if th e t ap e is c ut in t w o ju st at the p ea k of the sou nd , thereby bre a k in g it off abru p tly, a nd the t w o p a rts a re lin ked by a piec e of bla n k tap e , either of the t w o h a lv e s w ill m a k e the fem a le ap p ro ac h . S e n sit iv it y t o t h e v a rio u s p a rt s o f t h e so u n d sp ec tru m d iffers for d ifferent in sec ts--and som e c an hear in the u ltrason ic range. Ju st as bees c an se e u ltrav iolet lig ht , m oth s c a n hea r u ltra son ic sou nd- a n ad ap tation to d e te c t their enem ie s the b ats, w ho se c a lls a re la rge ly u ltra son ic . Verte brate s, for the m o st p a rt , he a r v er y w e ll. Even the fi she s, w h ich w ere thou g ht u ntil fa irly re c ently to b e q u ite d e a f, not on ly h av e a w e lldevelop ed hea rin g sen se but a lso c om m u n ic ate by sou nd s. F ro g s a nd to ad s, m a ny re p tile s a nd o f c o u rse b ird s a n d m a m m a ls a ll p ro d u c e a b e w ild erin g v a rie t y of so u nd s w ith o u t w h ic h the c ou ntr y sid e w ou ld se em v er y d e so late indeed . M o st of these sou nd s ac t as so cia l sig na ls, a n d m o st o f t h e m in d ic at e a g o o d a b ilit y t o d isc rim in ate p itc h . T h e c h a m p io n s o f h e a rin g , b y a n y st a n d a rd , a re the bats. B at sou nd s lon g w ent u nd ete c te d b e c au se the y a re pitc he d t w o to th re e o c tav e s ab ov e w h at w e c a n he a r. Very fe w hu m a n e a rs c a n d e t e c t a ir v ib ra t io n s w it h f re q u e n c ie s h ig h er th a n som e 2 0 ,0 0 0 p er se c on d , a n d th e av era ge lim it of hu m a n h e a rin g is d o w n n e a r 14,0 0 0 c yc le s. B ats, how e v er, pro d uc e a nd hea r


sou nd s of u p to a nd ov er 10 0 ,0 0 0 v ibration s p er se c ond . M ore ov er, the se sou nd s a re very loud : if w e w ere able to hea r them , the y w ou ld sou nd lik e the sc re a m of a je t fi g hter at c lo se ra n ge . To a nu m b er of b ats fl y in g a rou nd on a c a lm , still su m m er e v en in g , a nd to the u n fo rt u n at e m o th s w h ic h c a n h e a r th e m a n d m u st t r y t o av o id them , the e ven in g is a ny th in g but c a lm . It is a n in ferno of c on sta nt sh riek in g , eac h bat em ittin g a serie s of sc rea m s in e x trem e ly short p u lse s of le ss th a n a hu nd re d th of a se c ond in d u ration .

Feelers Whirligig beetles are surface swimmers, and as they glide about on ponds they rest their feelers just on top of the water. These feelers are equipped with pads of sensory hairs which detect not only surface ripples made by other moving in-

sects but even the presence of motionless W h at is im p orta nt to the b at is not the sou nd but its e c ho : b ou nc - objects such as rocks in g off ob stac le s lik e tre e s, w a lls a nd e ven fly in g in se c ts, th is k e e p s the b at in form e d , a s son a r d o e s a su bm a rine , of th in g s in its w ay a n d fo o d o n th e w in g . T h is e c h o -lo c at io n d e v ic e h a s e v o lv e d in d ifferent b ats in d ifferent w ay s- som e send o u t a w id e , sc at tere d b e a m , others a n a rro w one w h ic h c a n b e c h a n ge d in its d ire c tion a nd thu s u se d a s a sc a n n in g d e v ic e . W e k no w th at the m e c h a n ic s o f th is inv o lv e s th e b at s’ e a rs , m o u th a n d , in so m e sp e c ie s , n o se , b e c au se if a ny of the se a re blo c k e d , the y fl y “blind . “ B u t ho w the bats ‘ ea rs a nd bra in s pro c e ss the in form ation the y re c eive from the e c ho e s is still a m y stery-their au d itory ap p a rat u s m u st b e of g re at c om p le x it y. W h a le s u se a sim ila r son a r sy stem in the w ater. It h a s lon g b e en k now n th at w h a le s c ou ld hea r-read ers of M o by D ic k w ill re c a ll th at sp erm w h a le s m u st b e ap p ro ac he d v er y q u ie tly-a nd it is a lso no ne w s th at th e y m a k e so u nd s. B ritish sa ilors c a lle d one p a rt ic u la rly a rt ic u lat e sp e c ie s , th e a rc t ic b e lu ga w h a le , th e “se a 19


The Sense Organs

c a n a ry.” But the fu ll story w as not revea led u ntil W o rld W a r II, w h e n h y d ro p h o n e s , d e v e lo p e d for the d e te c tion of su bm a rine s, p ic k e d u p the a m az in g va riet y of u nderw ater noises w h ich a re produced by w ha les and dolph in s. W e k now now th at at le a st som e w h a le s c a n e m it u lt ra son ic sou nd s as h ig h as tho se of bats, a lthou g h w e still do not u nderstand how they produce them , since t h e y h av e n o v o c a l c o rd s . W e k n o w a lso t h at th e y u se e c h o lo c at io n fo r av o id in g o b st ac le s a nd for fi nd in g p re y, a nd th at the y h av e a v o c a l “ la n g u a ge ” for so c ia l c om m u n ic ation . F u rth er inv e stigation s lik e th o se a lre ad y c onduc ted w ith p orp oises in the M a rina l and aqu a ria of F lorid a a nd C a liforn ia m ay revea l still other asp ec ts of w ha le life. For in stance, it m ay ex pla in the p u z z lin g p henom enon of m a ss stra nd in g s a nd death s of w ha les in sha llow w ater. For m a ny yea rs nob o d y c ou ld u ndersta nd w hy the se hu ge c re at u re s so m e t im e s c a m e into sh a llo w s , go t st u c k th e re a n d d ie d o f su ffo c at io n w h e n th e w eig ht of their b o d ie s, no lon ger su p p orte d b y the w ater, m ade it im p o ssible for them to in fl ate their lu n gs prop erly. N ow it has been p ointed out th at stra nd in g s o c c u r a lm o st a lw ay s on gently slopin g sa nd y or m u d d y b ot tom s, p re c ise ly the p lac e s w h e re t h e c o a st lin e w o u ld fa il t o g iv e e x ac t e c h o -lo c at io n in fo rm at io n su c h a s t h e w h a le s w ou ld ge t on ste e p er ro c k y c o a sts. Still v er y m y steriou s a re the latera l line orga n s p ossessed by m any fishes and . som e frogs. T hese a re m ad e u p of p its or g ro o v e s a rra n ge d a lon g the b o d y su rfac e , e ac h c onta in in g ro w s of sensory c ells. F rom each c ell protrude protoplasm ic “ h a irs” w h ic h re sp o n d t o th e slig ht e st m o v e m ents of the su rrou nd in g w ater su c h a s m ig ht b e c au se d b y the ap p ro ac h of a p re y or a nother fi sh . T he h a irs a re e x trem e ly sen sitiv e a nd , lik e e a rs, c a n re c eiv e in form ation from d ista nt o b jec ts. B ec au se of their g reat sen sitiv it y, excessive stim u lation m ay b e ac tu a lly p a in fu l - m a ny territoria l fi sh w a rd off intruders w ith stron g b eats 20

o f t h e ir t a ils w h ic h , w it h o u t t o u c h in g t h e m , m ay b e a s e ffe c t iv e a s d ire c t b lo w s .Ju st a s a ll sou nd- a nd e c ho -lo c atin g d e v ic e s a re b a sic a lly m e c h a n ic a l, the q u a litie s of sm e ll a nd ta ste a re often lu m p e d to ge ther a s the c hem ic a l sen se s. Sm ell is genera lly u sed for prelim ina ry ex a m ination of th in gs, som etim e s at a d ista nc e ; taste for th in gs ac tu a lly touched , as food is tasted w hen it is in the m outh . T he d istinc tion s b et w e en sm ell a nd t a ste blu r w hen w e c on sid er the c hem ic a l sen sitiv it y of the lo w er a n im a ls, but v ery m a ny of them d o h av e a c hem ic a l sen se for d ista nc e p e rc e p t io n a n d a n o th e r fo r th e fi n a l c h e c k o f fo o d b efore it is sw a llo w e d .

Sonar It c om e s a s no su rp rise to le a rn th at m a ny a n im a ls have better chem ic a l sen se orga n s tha n w e h ave a nd th at the y u se them in q u ite a d ifferent w ay. E v en a m on g ou r c lo se re lativ e s, the m a m m a ls, w e c u t a p o or fi g u re . T he w orld of sm e lls in w h ic h a d o g m u st liv e w ou ld b e b e w ild erin g to a hu m a n- a go o d t rac k in g d o g c a n fo llo w a sin g le sc ent th rou g h a m ix t u re of other sc ents w ith u nc a n ny c erta int y. M a m m a lia n pre d ators u se sm e ll e x t e n siv e ly fo r t rac k in g t h e ir p re y ; a n d t h e p re y e d -u p o n t o av o id t h e ir h u n t e rs . O ne a n im a l le ss w e ll end o w e d m ay e v en m a k e u se of a su p erior no se b elon g in g to a nother. It is a c om m on sig ht in the A fric a n sav a n n a to se e babo on s a nd im p a las travelin g together, the im p a la p ro fitin g from the b ab o on‘s k e en e y e sig ht , the b ab o on from the im p a la‘s sen se of sm e ll. M o st c om m on ly-a nd q u ite lo g ic a lly-the sen se of sm e ll in v erte brate s is lo c ate d ne a r the front end , in the no se . T h is m ay b e su p p lem ente d b y a n o t h e r se n sin g d e v ic e k n o w n a s Jac o b so n’s organ , com m on am on g m any reptiles. Jacobson’s organ is ac tu a lly a sm a ll c av it y in the head ; it has no e x tern a l op en in g , but op en s into the ro of of the m outh . W hether it shou ld be c a lled a tastin g or a sm ellin g orga n is d iffic u lt to say, em ph a siz -


in g a ga in the fac t th at the se t w o sen se s ov erlap som e w h at in m o st a n im a ls, sinc e the y b oth d e p end on c hem ic a l a n a ly sis. Jac o b son’s orga n is lin e d w ith sen sin g c e lls w h ic h “ sm e ll” b y re sp on d in g to m o le c u le s in th e a ir. T h e re a son a sn a k e c on st a nt ly fl ic k s o u t its fork e d ton g u e is th at it is te stin g the a ir, c olle c tin g a sm a ll sa m p le o n it s t o n g u e , w h ic h is t h e n b ro u g h t b ac k in t o t h e m o u t h a n d in se rt e d int o Jac o b so n’s o rga n fo r a n a ly sis . N e w t s h av e n o su c h t o n g u e s b u t , b e in g a m p h ibia n s , h av e e v o lv e d n o se s th at c a n b e u se d b oth in the a ir a nd u nd er w ater.

Organ Analysis The reason a snake constantly flicks out its forked tongue is that it is test-

ing the air, collecting a small sample on A sen se orga n w h ic h is entire ly a lien to u s is a sso c iate d w ith th e its tongue, which is then brought back c u riou s elec tric “battery ” fou nd in som e fi shes. T he fac t that c erta in sp e c ie s, lik e the e le c tric e e l of S ou th A m eric a , c a n d e liv er p o w er- into the mouth and inserted into Jacobson’s fu l e le c tric sho c k s a s a m e a n s of d efen se a ga in st p re d ators a nd of organ for analysis. st u n n in g p re y h a s lon g b e en k n o w n , bu t it is on ly q u ite re c ent ly th at sc ie nt ist s h av e re a liz e d th e re is m o re to th e e le c t ric o rga n s th a n th at . T he y a re no w c on sid ere d to b e e x trem e sp e c ia liz ation s o f m u c h m o re c o m m o n o rg a n s w h ic h c re at e v e r y w e a k e le c t ric c u rrents a nd a re u se d to lo c ate o b stac le s a nd pre y. In other w ord s, the “six th sen se ” p o sse sse d b y su c h fi she s is a h ig h d e g re e of sensit iv it y t o e le c t ric a l fi e ld s .A n o u t st a n d in g e x a m p le o f th is is a n A fric a n fre sh-w ate r fi sh , G y m n a rc hu s n ilo t ic u s , w h ic h h a s a se t of m u sc le s in its ta il th at h av e lo st the p o w er to c ontrac t . In ste ad , the y send ou t a c ontinu ou s stre a m of w e a k e le c tric d isc h a rge s, at a rate of ab o u t 3 0 0 p er se c ond . D u rin g e ac h d isc h a rge , th e t a il is 21


The Sense Organs

m om enta rily e le c tric a lly negativ e w ith re sp e c t to the he ad of the fi sh . T hu s the fi sh generate s in its env iron m ent a t w o -p o le d fie ld of e le c tric c u rre nt , a n d it c a n se n se w e a k d ist u rb a n c e s in th is fie ld . T h e se n se o rga n s a re lo c at e d in a n d n e a r th e h e a d a n d c o n sist o f p o re s in t h e t h ic k s k in , w h ic h it s e lf is n o n c o n d u c t in g . T h e s e p o re s le ad int o je lly-fi lle d c h a n n e ls . A t t h e b o t t o m of the se c h a n ne ls a re fou nd g rou p s of sen sor y c e lls w h ic h h av e e lab orate n er v e c on n e c tion s w ith the bra in . It is p o ssible to tra in such fi sh to d isc rim in ate b et w e en a nonc ond u c tin g o bje c t , su c h a s a pie c e of g la ss su sp end e d in the w ater, a n d a n id e nt ic a lly sh ap e d c o n d u c t in g o bje c t , su c h a s a p orou s t u b e fi lle d w ith a sa lt solution or w ith ac id . T he se o bje c ts d istort the e le c tric fie ld a rou nd the fi sh in d ifferent w ay s, a nd the fi sh c a n fe e l the se d ifferenc e s on the su rfac e of its b o d y. T he p hy sio lo g y of the se sen se orga n s is still not q u ite k no w n , bu t their e x trem e sensitiv it y is a lre ad y c le a rly p ro v e d . W ith th is apparatu s, G y m narchu s can not detec t fi sh th at a re m ore th a n fou r inche s aw ay from it. H ow ever, d ista nce is not p a rtic u la rly im p orta nt, sin c e th e se fi sh liv e in d e n se ly p o p u late d a n d t u rbid w aters w here v isibilit y is v er y p o or a lso the y a re no c t u rn a l. T h is brief re v ie w c a n not p o ssibly prov id e m ore th a n a g lim p se into the fa sc in atin g w orld of the sen se s. T here a re c ert a in ly m ore sen se orga n s th a n I h av e m entione d . S om e m a rine a n im a ls, fo r in st a n c e , re sp o n d t o slig h t d iffe re n c e s in

22

sa lin it y. O ther a n im a ls c a n d e te c t d ifferenc e s in the hu m id it y of the a ir; b e e s u se th is abilit y to fi nd their w ay to the ne c t a r in a flo w er, a nd liz a rd s to fi nd their w ay to w ater. M a ny a n im a ls p erform fe ats of orientation th at still b a ffle the sc ientist . N o one h a s y e t b e en able fu lly to e xpla in hom in g in bird s or the m ig ration of m a rine fi sh e s . A n d t h e re a re m a n y lo w e r a n im a ls in the sea th at ap p a rently sen se d ifferenc e s in the tid e s, sp aw n in g on ly du rin g sprin g tid e s, or fu ll m o on a nd ne w m o on tid e s. H o w th e y c a n te ll w h ic h is w h ic h w e d o not k no w ­— p erh ap s the y re g ister su btle flu c t u ation s in p re ssu re , w h ic h w ou ld b e g re ate st d u rin g sp rin g tid e s. A nd w hat about p erception that goes beyond the sen ses that w e k now ? T h is is c a lled ex trasen sory p erc e p tion , a nd it is a n issue blu rre d by v a riou s fac tors, of w h ic h im p re c ise term inolo g y is one . If on e d e fi n e s a sen se orga n a s a ny orga n th at prov id e s a n a n im a l w ith in form ation ab out the o u t sid e w o rld , th e re is p e r d e fi n it io n n o su c h th in g a s e x tra sen sory p erc e p tion . O n the other h a nd , if one ap p lie s the term to p erc e p tion b y p ro c e sse s not y e t k no w n to u s, then e x tra senso r y p e rc e p t io n a m o n g liv in g c re at u re s m ay w e ll o c c u r w id e ly. In fac t , the e c ho lo c ation of b ats , ‘the fu nc tion s of the latera l line in fi she s a n d th e w ay e le c t ric fi sh e s fi n d th e ir p re y a re a ll b a se d on p ro c e sse s w h ic h w e d id not k no w a b o u t-a n d w h ic h ~e re thu s “e x t ra se n so r y ” in th is sen se -on ly 2 5 y e a rs a go . T here is no p oint in qu a rrelin g about a term -w hat w e c an a ll ag ree on is th at w e m u st c ontinu e ou r st u d ie s of the a n im a l’s w ind o w s to the w orld .


One animal less well endowed may even make use of a superior nose belonging to another. It is a common sight in the African savanna to see baboons and impalas traveling together, the impala profiting from the baboon‘s keen eyesight, the baboon from the impala‘s sense of smell.

23


The Sense Organs

24


Senses: means to an end All animals, from the lowest on the evolutionary scale to the highest, manifest behavior of some sort. Though all share one world, all may be said to live in different worlds, since each perceives best only that part of the environment essential to its success. Thus, how an animal behaves has much to do with what its sense organs are and whether these are few or many, simple or complex.

25


The Sense Organs

2.

1.

Feelers for smelling / hairs for tasting Although among most animals the head serves as the repository of the major sense organs, there are many in which some or all of these organs lie else where either because the head is too small or does not exist at all, or because another part of the body has proved more

1. Tasting food with the sensory hairs on its feet, a house fly lets down its elephant like proboscis and

suitable for their development. The headless mussel

begins to feed. The square shows the area of the

has developed eyes and tentacles for tasting that lie

proboscis to be examined in ever finer detail below.

around the edge of its shell. Some sea snails carry their eyes on their backs, tube worms have them on

2. The proboscis is shown to have two lobes. The fly

the tips of their tentacles. Grasshoppers hear with

eats by pressing the proboscis against food, particles

organs on their legs or abdomens. Many moths and

of which are drawn up through pores and the cavity

butterflies smell with their antennae. Flies taste with

between the lobes.

countless hairs on their feet and must first step on their food (below) in order to become ~sufficiently stimulated to eat it. 26


Flower as seen by man

Beyond the senses of Man As far as the senses go, the world is not as it seems. Perception must vary from one kind of animal to another, since the sense organs rarely, if ever, have exactly the same range. Take man and bee. Because the human eye reacts to light waves only of a certain length, man fails to respond to the shorter and longer waves of the optical spectrum. The bee is not so hampered-at least as far as the shorter waves go—­and can actually see ultraviolet. Thus, to the bee a flower may display a pattern etched in ultraviolet (left) that impels the bee toward the nectar. But should the flower be red, the bee would see it as black, simply because its eyes do not register the longer light waves. At the other end of the visible spectrum, where red becomes infrared, man goes “blind” himself, yet a creature like the diamondback rattler has its own way of perceiving it.

27


The Sense Organs

Mouth cavity

Jacobson’s organ Cartilage of nasal septum

Jacobson’s organ

Brain

28


The scaly head Of a diamondback rattlesnake exhibits uncommon sense organs a pit beneath each eye that enables the snake to detect its warm-blooded prey through infrared radiation.Containing numerous, tightly packed nerve endings, the pits respond to heat but not to light, and thus let the diamondback locate food in the dark, when it usually does its hunting. 29


The Sense Organs

The sense of sight / new light on an ancient subject Among different animals, different senses dominate, made with cameras and insect eyes-investigators In birds, sight does; in most mammals, smell and thought that if they could take photographs through hearing do. Fishes can be said to rely upon smell the eyes, they might see the world as an insect does. and touch for information about their environment; Nothing could be further from the truth. most insects upon smell and taste. Man uses all of these senses, but again, as with other animals, one sense dominates, and this sense, of course, is sight. Because he leans on sight so heavily, man naturally enough has long tended to consider the world in a visual way; not only has he assumed that ‘most other animals depend on their eyes more than they actually do but he has also assumed that they see the way he does. That accounts for the numerous experiments 30

Misconceptions about vision can be attributed not only to human bias but to incomplete and often inaccurate information about the different kinds of eyes in the animal kingdom. Man’s understanding of even his own eye has been amazingly slow in coming, and for centuries was based upon the false notion, first propounded by the ancient Greeks, that the lens captured the image and that the retina nourished the lens and conveyed to it, from the brain through the optic


nerve, a mysterious power called the “visual spirit.”

an image, a faint, fleeting record of what the eye had

Not until late in the 16th Century was the Greek view

been taking in at the moment its owner had died.

seriously challenged, by the Swiss anatomist Platter,

When, late in the 19th Century, it became possible

who proposed that the lens captured light instead and

to fix such an image on the retina with chemicals and

distributed it over the retina. The German astronomer

produce something called an optogram, the notion of

Kepler suggested in 1604 that the image was some-

the eye as a pinhole camera gained wide acceptance

how” painted” on the retina, A few years later a Jesuit

and persists today. Such a notion, however valid,

friar named Scheiner offered dramatic proof of this-in

does nothing to explain what happens to the image

peeling away the opaque layers at the Vishniac. To

once it has fallen on the retina, a fascinating problem

prepare the eye, Dr. Vishniac had first to clear away

that is only just beginning to be solved. Some of the

all nerves and muscles with tiny needlelike spines

startling discoveries made to date are depicted and

from a fresh-water sponge, a task that took about 18

explored on the following pages- in several instances

hours to finish. Back of the eye, he actually laid bare

for the first time anywhere outside scientific journals. 31


The Sense Organs

The anatomy of vision / the Image on the retina It may never be possible to show exactly what any a sensitive screen in the retina. Light striking this animal actually sees. But as the paintings on these screen excites each cell individually, and together the and the following pages demonstrate, it is possible light-stimulated cells form a mosaic like pattern, an to show in a schematic way not only what the image image of what the eye is looking at. falling on the rear wall of the eye or retina may look like in various animals but also how the retina transforms this image into visual information of use to the brain in initiating behavior.

This, the first major step in the process of vision, is the subject of the diagrams at right. What the animal will ultimately see (shown on the following pages) depends on how its retina and brain process the mosaic. Here

The eye alone, of course, never sees: the brain sees. are shown the three kinds of image-forming eyes that What the eye does in its most basic role is to register have evolved in the animal kingdom, each looking at light. To this end, all eyes, from the simplest to the the same starlike shape from the same distance. In most complex, have in common light-sensitive cells. the first two, the tiny squares represent the individual These cells, thousands of them packed together, forms receptors; in the third, the facets do. 32


Insect eye

Human eye

Consists of many tiny units, each of which

Like a camera, with a diaphragm (the iris) The most advanced visual apparatus of any

may be said to be an eye in itself, since

to regulate the amount of light passing found among the invertebrates, has evolved

each has its own lens and light sensitive

into it through the pupil, an elastic lens independently of the vertebrate eye, yet,

cells connected to the brain. These little

to focus the light, and film (the receptors with a few obvious differences such as a

“eyes� may number from less than 12

of the retina) to record the light. Although rectangular pupil and two protective coats

in some cave-dwelling insects to more

far from perfect optically, it is superior to instead of one, it shares many of its basic

than 28,000 in the dragonfly. Because

the eyes of many other vertebrates. The features. Here again the eye operates on

of their tapered shape, they face outward

human eye is characterized by its recep- the principle of a camera. However, the im-

in slightly different directions, and thus

tors, some 130 million tightly packed age, as registered by the receptors (above),

each takes in a different part of the scene.

rods and cones which connect to about is smaller-because the eye itself is smaller.

The painting above shows how the facet

one million optic nerve fibers. The image It is also much less precise, not because of

aimed directly at the starlike shape receives

they form (above) shows a remarkable any inability of the muscle-controlled lens

the complete image, while the surrounding

fineness and seems all of a piece when to focus clearly, but because the receptors

facets receive only part of it.

Octopus eye

reassembled in the brain, although in fact are fewer in number and proportionately it is a mosaic on the retina.

bigger- and thus produce a coarser mosaic.

33


The Sense Organs

Vision two / the eye and the brain The recording of an image on the retina, as has already

does not activate the outer layers, but does activate

been shown, is but the first step in vision. The second

the receptors, which initiate signals that travel in the

step involves getting the image to the brain in useful

direction of the red the cats retina. Oddly enough, has

form. These diagrams show in broadest an octopus

only two kinds of ganglion cells, as opposed to four

retina contains only receptor cells, shown at left in

kinds for the frog, although its owner is a more highly

purple. These cells react individually to light and to-

developed vertebrate. A way to characterize it would be

gether form an image. Each sends a signal directly to

to describe it as less orderly-the ganglion cells display

the brain along a fiber, which combines with thousands

an almost haphazard connection to the bipolar cells.

of other such fibers into a many-stranded single cable

Even so, the nerve impulses coming from the receptors

to form the optic nerve. Via this cable the signals get

follow the same basic route to the brain. Outline how

to the optic lobes, two bean-shaped masses which

this is accomplished in an invertebrate (an octopus)

form a large part of the frog’s retina is much more

and two vertebrates (a frog and a cat), The octopus

complicated than the octopus. It has three layers of

has a relatively simple retina, consisting of a single

nerve cells instead of one: an inner layer of receptors,

layer of receptor cells which transmit visual information

a middle layer of bipolar cells and an outer layer of

directly to the brain for processing. The frog and the

ganglion cells. Light entering the eye (yellow arrows)

cat-in fact, all vertebrates the octopus ' brain. Here

34


the signals, or visual information, are processed and, tenth go to a reflex center like ' that of the frog. The in ways as yet unknown, put to use by the octopus. other nine tenths connect to cells in a kind of relay The octopus is able to see remarkably well because of station ( dotted circle, blue), before being sent on for the high development of its eyes and central nervous final processing to the cerebral cortex. This arrangesystem. It can also distinguish between shapes, which, ment would apparently give the cat a broader choice in considering the limited amount of visual interpretation responding to what it sees than the reflex-dominated that the average invertebrate can make, is amazing. frog. Have much more complicated retinas, made up Arrows-back through the bipolar and ganglion cells of three separate layers of nerve cells. Light enterand via the optic nerve to the brain. Reflecting the ing the eye passes right through the cells of the first importance of speed to the insect–eating frog, nine two layers, without affecting them, on its way to the tenths of the visual information gets processed right receptors at back. Here it triggers nerve impulses in the retina and then is forwarded directly to a reflex electrical signals which pass from the receptors to center in the brain, where it is acted upon almost at the bipolar cells for initial processing and then on to once. Is it any wonder that the frog has been described the ganglion cells for further processing, and finally as a living catapult? But something different happens along the fibers that form the optic nerve to the brain to the impulse when they reach the brain. Only one for still further processing. 35


The Sense Organs

Vision three / layers of the retina The vertebrate retina is characterized by its complexity.

controls the nature of the signal which travels through

The painting on the right is a highly magnified cross

it. There are even greater differences of size and of

section of a frog's retina, showing the three layers of

structure among the ganglion cells than among the

cells already described: receptors ( green), bipolar

bipolar cells. The type shown in red, for example, is

cells (blue ) and the ganglion cells (orange ). The

relatively scarce but has a huge network of far reaching

receptors are the only cells sensitive to light; the

branches which connects up with a great many bipolar

bipolar cells are essentially links between the recep-

cells and thereby enables it to collect information from

tors and the ganglion cells. However, their linkages

a large area of the retina. Although the orange type

vary- some of them connect with one receptor, some

connects with bipolar cells at two levels, it receives

with several; some of them meet the ganglion cells

information from a more restricted area. The tan

halfway, others send fibers almost to the bodies of

type, which also connects to the bipolar cells at two

the cells themselves. These variations in linkage are

levels, is more numerous than the orange type but

believed to make possible the first step in processing

receives information from an even smaller area. And

the visual information, much as the wiring in a radio

the green type, the most numerous of all, receives

36


Receptor cells

Bipolar cells

Ganglion cells

information from the smallest area. The effect of this complex circuitry is astonishing: it permits the four kinds of ganglion cells to take the visual information coming from the receptors and to analyze it in four different ways. The red type, for example, seems to fire only when there is a decrease in light- -a dimming or darkening of whatever the eye is observing--and thus presumably it conveys to the brain information about large, dark shapes. The orange kind is believed to respond to fairly big moving objects, and the tan to smaller moving objects with curved or pointed edges, such as insects or the tips of wind-tossed grass. The green is activated only by abrupt, contrasting edges of light and dark. 37


The Sense Organs

38


Instinct vs. Learning

2

T here is a c atc h ph ra se , still w id ely u se d thou g h thorou g h ly outd ate d , w h ic h say s th at “ a n im a ls ac t in stinc tiv e ly, bu t m a n ac ts inte lligently. “ L ik e m a ny su c h genera l statem ents, th is c ou ld b e interp re te d in v a riou s w ay s, bu t it is ge n e ra lly t a k e n to re fe r to th e w ay b e h av io r d e v e lo p s in a n in d iv id u a l th e p oint b ein g th at a n im a ls a re b orn w ith a g reat dea l of their ad ap tive b eh av ior, so to sp e a k , re ad y-m ad e , w here a s m a n m u st le a rn m o st of h is. O f c ou rse , w e k no w no w th at th is is not a lto ge ther tru e , th at there is a g re at d e a l m ore to the story of how b eh av ior, in a ll its intric ate ade p tne ss, de velop s in the c ou rse of a n a n im a l’s life , T h is is the genera l stor y w e sh a ll c on sid er no w. M a ny a n im a ls d o n ot b e h av e e ffic ient ly “ from th e w ord go ,” a s a m ac h in e do e s, nor do a n im a ls k e e p the sa m e b eh av ior p attern s th rou g hout their live s, T h eir b e h av ior m ac h iner y c h a n ge s a s th e y g ro w u p - som e tim e s g rad u a lly, a s a tad p o le‘s w rig g lin g in the e g g c a se d e v e lo p s later into w av y sw im m in g m otion s for the w ater, or a hu m a n in fa nt ’s w a lk in g e v o lv e s o v er a p erio d of yea rs, S om e c h a n ge s, on the other h a nd , a re abru p t a nd sp e c tac u la r: a ne w ly h atc he d bu t terfl y su d d en ly ta k e s off a nd fl ie s ; a n eid er d u c k lin g t w o hou rs

39


Instinct vs. Learning

old m a k e s a p erfe c t sp la sh d iv e into the w ater o n it s fi rst t r y ; a b ab y c h im p a n z e e in th e z o o su d d en ly t u rn s a som ersau lt a nd from then on d o e s it often . S om e c h a n ge s o c c u r e a rly in life a c u t t le fi sh ju st o u t o f th e e g g v e r y e ffic ient ly c atc he s the fi rst M y sis sh rim p it se e s-bu t othe rs , lik e t h e re p ro d u c t iv e ac t iv it ie s o f h ig h e r a n im a ls , o c c u r m u c h lat e r’. T h e c h a n g e s w e s e e m o st e a sily a re t h o s e in t h e m o v e m e n t s t h e m se lv e s , o r m o t o r p at t e rn s , a s w h e n y o u r p e t p u p p y le a rn s t o c o m e w h e n y o u w h ist le . H o w e v e r, su c h c h a n ge s in v o lv e h id d e n p a rt s of the m ac h inery a s w e ll. You m ig ht th in k th at w h at the pu p p y h a s lea rne d is “ru n n in g tow a rd y ou”; ac t u a lly he h a s le a rne d “ru n n in g to w a rd y o u in re sp o n se t o a st im u lu s w h ic h d id n o t e lic it th is b eh av ior b efore . “ O u r k now le d ge of such b eh av ior ch a n ge s in the c o u rse of a n a n im a l’s d e v e lo p m ent is m e a ger, but w e do k now enou g h to say th at the ch a n ge s a re often d ra stic a nd of m a ny k ind s. · C on sid er, for e x a m p le , the c h a n g in g ac tiv itie s of a you n g g u ll in its fi rst m onth of life . T he c h ic k ‘s in itia l ac t in e nt e rin g th e w o rld c o n sist s o f p u sh in g o ff t h e e g g ’s “lid ” t h ro u g h a se rie s o f fo rc e f u l stretc h in g m ov em ents of the ne c k . T he sp e c ia l m u sc le u se d for th is sh rin k s a fter it h as done its dut y. In the ne st , the ch ic k ~ill at fi rst lie q u ietly, bro o de d by the p a rent. In a fe w hou rs its dow ny p lu m a ge d rie s a nd b e c om e s flu ff y. A lre ad y b e fore it is d ry it w ill beg in to m a ke fe eble p e c k in g m ovem ents at the p a rent ‘s bill tip w hene ver the p a rent b end s d o w n ov er the ne st . T he se p e c k s in c re a se rap id ly in fre q u e n c y, a n d p e rh ap s in ac c u rac y to o , a nd so on the p a rent w ill re sp ond b y re g u rg itatin g fo o d . T he c h ic k ta k e s u p th is fo o d a nd sw a llo w s it . D u rin g the ne x t hou rs it w ill at t e m p t t o ge t u p o n it s le g s , at fi rst in a h a lf hea rte d w ay, but so on it w ill sta nd u prig ht . N ow fu lly in the w orld , the ch ick beg in s to preen 40

its p lu m a ge . B efore the d ay is ou t it w ill ta k e a fe w c lu m sy ste p s, a nd w hen it is one d ay o ld it m ay e v en w a lk ou t of the ne st . W hen the g u ll c o lony is d ist u rb e d b y a p re d ator th e p a rent s w ill fl y u p a n d c a ll th e a la rm , w h e re u p o n th e ch ic k w ill c rouch . W hen it is on ly a fe w d ay s old t h e a la rm c a ll w ill e lic it a c o n sid e ra b ly m o re c om p le x re sp on se : the c h ic k w ill fi rst ru n ou t of the ne st , enter c o v er a nd then c rou c h . S o on e ac h c h ic k o n su c h o c c a sio n s w ill ru n to o n e p a rtic u la r h id in g p lac e . W ith in a w e e k a c h ic k w ill b e g in to m a k e fl y in g m o v em ents. W ith in t w o w e ek s it w ill b eg in to c a ll at stra n gers, a nd so on a fter it w ill d ash at them a nd attac k them . S t ill lat e r, t h e c h ic k b e g in s t o fe e d in d e p e n d e nt ly. It st a r t s b y p e c k in g in d isc rim in at e ly at m a n y d iffe re nt o bje c t s , bu t a fte r a w h ile it ig nore s ine d ible obje c ts a nd eats on ly rea l fo o d . T h e fl y in g m o v e m e nt s b e c o m e st ro n ge r, a n d w hen the c h ic k is fou r to fi v e w e e k s o ld it c a n fly. B ut its la nd in g is still v ery c lu m sy ; at fi rst it w ill a lig ht w ithout rega rd for w ind d irec tion and force, a nd it m ay tu m ble over t w o or th ree tim es w hen it la nd s w ith a stron g t a ilw ind . W hen it se e s w ater for th e fi rst tim e , it m ay d ip its bill into it a nd m ay then d rin k . B u t w h ile at fi rst it w ill tr y to d rin k from a ny g lit terin g su rfac e , it w ill so on re c o g n iz e w ater a s su c h . A fter d rin kin g , it m ay b eg in to m a k e bath in g m ov em ents, bu t d ay s w ill p a ss b efore it w ill ac t u a lly b athe in t h e w at e r. A t fi rst it m ay e v e n m a k e t h e se m ov em ents w h ile sta nd in g on la nd , but fac in g the w ater th at h a s w e t te d its bill. T h is is ty pic a l of how behav ior develop s in m any a n im a ls. S om e m ov em ents a re p erform e d re as o n a b ly w e ll o r e v e n p e r fe c t ly t h e fi rst t im e th e y a re d o n e ; o th e rs d e v e lo p g rad u a lly. A t a g la n c e o n e is in c lin e d t o say o f t h e fi rst t y p e th at the y m u st b e in n ate , a nd th at the se c ond t y p e of de velopm ent re vea ls a g radu a l lea rn in g.


C on sider, for in sta nc e , the w ay the ch ic k c rouche s the fi rst tim e the p a rent g u lls fl y u p in a la rm . T h is lo ok s lik e non le a rne d b eh av ior, a n d it m ay w e ll b e ; b u t o n t h e o t h e r h a n d , t h e c h ic k c o u ld h av e he a rd the a la rm c a ll b efore , w h ile still in the e g g , a nd it m ay h av e asso c iate d th is w ith the ch illin g c au se d by the ex p o su re of the eg gs. T hu s c rou c h in g c ou ld orig in a lly h av e b e en a re sp on se to c h illin g a nd on ly later a sso c iate d w ith the a la rm c a ll. C onversely, the g radu a l de velopm ent of the fly in g m ovem ent w ou ld se em to b e d u e to the c h ic k ‘s c ontinuou s prac tic in g . T h is h a s b e en te ste d in e x p erim ents w ith you n g pige on s re a re d in n a rrow e a rthenw a re t u b e s in w h ic h the y sim p ly c ou ld not m a k e the ne c e ssa r y prac tic in g m ov em ents. Yet w hen the “tu b e bird s” w ere re lea se d for the fi rst tim e , sim u lta ne ou sly w ith norm a l y ou n g of the sa m e a ge w ho had ju st lea rned to fly, they flew ju st as w ell as the norm a l bird s ! O bv iou sly the g radu a l im provem ent ob serve d u nder norm a l c ond ition s c a n o c c u r w ithout p rac tic e ; the c lu m sy n at u re of the c h ic k ‘s e a rly at tem p ts m ay w e ll h av e b e en d u e sim p ly to the fac t th at the u rge to fl y w a s there b efore the w in g s a nd the fl y in g m u sc le s w ere fu lly de velop e d . T h is go e s to show th at m ere observation s, how e ver p re c ise , c a n b e m isle ad in g . If w e w a nt to ge t re liable in form ation a s to w he ther a c erta in t y p e of b eh av ior c h a n ge s th rou g h le a rn in g or d e v e lop s in n ate ly (or p erh ap s th rou g h a c om bin ation of the t w o pro c e sse s), w e h ave to do e x p erim ents. But b efore I d isc u ss som e of the e x p erim ents th at h av e b e en d one it w ill b e u sefu l to form u late ou r p ro blem a lit tle m ore c le a rly. T he p henom enon w e w a nt to e x p la in is th at of c h a n ge in b eh av ior m ac h inery d u rin g d e v e lop m ent . T he se c h a n ge s a re m a ny. T he ap p ea ra nc e of a new behav ior p attern , or its d isap p ea ra nc e or, p erhap s m o st o fte n , th e p e rfe c tion o f a b e h av ior p at te rn-a ll th e se th in g s a re c h a n ge s a nd c a n b e re ad ily se en . B ut a n a n im a l‘s sen sitiv it y to stim u li ch a n ge s to o. T hu s, the m ere ob serv ation a nd d e sc rip tion of the se d e velopm ents of b eh av ior, no m atter how c a refu lly re c ord e d , a re no m ore th a n a sta rt . C on sid erably m ore d iffic u lt is fi nd in g out h o w th e se c h a n ge s a re bro u g ht ab o u t : w h at c au se s e ac h c h a n ge . T he fi rst ste p in such a n a n a ly sis is in princ iple the sa m e as in m a ny other b eh av ior st u d ie s : w e d istin g u ish b e t w e en c au se s w ith in the a n im a l a nd tho se ac tin g on it from outsid e . L et u s c on sid er outsid e c au se s fi rst . W hen a y ou n g go slin g h atc he s from the eg g , it is so on able to w a lk . T h is w a lk in g is d ire c te d : it b eg in s to follow its m other. A fte r it h a s fo llo w e d th e m oth e r for so m e tim e , it w ill n ot fo llo w 41

Where will he scratch? Afrog’s knowledge of what part of its body is itchy, and how to respond with a scratch, is accomplished by a delicate interplay of skin and connecting nerves, in which the chemical differences in different parts of the skin “educate” the nerves early in the frog’s life. An experiment demonstrating this is shown below.

First, a piece of back skin, dark in color and with its own individual chemical properties, was removed and a piece of white belly skin was grafted in its place.

Second, Then the back skin was grafted on the belly. These grafts were done before the nerves of the young frog had grown out to reach the skin and be affected by it.


Instinct vs. Learning

other a n im a ls. But if w e h atch a go slin g in a n inc u bator a nd pre sent it , not w ith its m other, but w ith a nother a n im a l or e v en som eth in g lik e a blu e b a llo on it w ill fo llo w th is abnorm a l o bje c t . A nd onc e it h a s fo llo w e d th e b a llo o n fo r so m e t im e , it w ill c o nt inu e to d o so a nd refu se to fo llo w a re a l m other go o se . In b eh av ior term s, it h a s b e c om e “im p rinte d ” on the a rtific ia l p a rent- on w h ate v er e lic ite d its fo llo w in g re sp on se fi rst . W h at th is show s is th at in ord er to b eh ave norm a lly— i.e . , to follow its m other­— the go slin g h ad to b e e x p o se d to the m other fi rst . To u se a n en g ine erin g term , the “ p ro g ra m m in g ” of the “follo w in g re sp on se” w a s not c om plete at h atch in g . W h ate ver the go slin g m ig ht h av e h ad in the w ay of a n in n ate re sp on se h ad to b e su p p lem ente d b y e x p o su re to the ou tsid e w orld . I n o t h e r c a s e s n o s u c h s u p p le m e n t a r y p ro g ra m m in g is re q u ire d : t h e re sp o n se is c le a rly n o t le a rn e d . If w e h at c h a b lac kh e ad e d g u ll c h ic k in a n in c u b at o r k e e p it in c o m p le t e d a rk n e ss fo r a fe w h o u rs a n d t h e n sh o w it m o d e ls o f t h e p a re nt ’s bill, w e fi n d t h at it re sp o n d s m o re v ig o ro u s ly t o re d m o d e ls-t h e n at u ra l c o lo r o f t h e a d u lt ‘s b ill- t h a n t o t h o s e o f a n y o t h e r c o lo r. S in c e t h e c h ic k h ad n e v e r se e n a n y t h in g , a n d c e r t a in ly n o t a n ad u lt g u ll, it s p ro g ra m m in g w ith re sp e c t to bill c o lor m u st h av e b e en d one intern a lly. F rom the se t w o e x a m p le s it is c le a r th at b eh av ior m ac h iner y c a n b e p ro g ra m m e d either from w ith in or from w ithou t . T he e x tern a l prog ram m ing is done th rou g h ind iv idu a l adju stm ents th rou g h ex p e rienc e . T he intern a l prog ra m m in g , as w e sh a ll se e later, is the re su lt of the slo w e v o lu tion of the a n im a l itse lf. It w a s ac h ie v e d th rou g h lon g interac tion w ith the env iron m ent in a k ind of ga m blin g-a tria lInternal instinct a nd-error pro c e ss- w h ic h th rou g h generation a fter generation gave The clue to the timid crouching of chicks n at u ra l se le c tion the c h a nc e to w e e d out fa ilu re s a nd p re serv e the lies in their innate tendency to do this when effic iently p ro g ra m m e d t y p e s. anything passes overhead, and even cringe L ike the “ follow in g resp on se,” m any other behav ior pattern s develop at falling leaves. As they grow older, they th rou g h ind iv id u a l interac tion w ith the env iron m ent . O ne of the slowly get used to these common objects Sim p le st is pro bably ju st gettin g u se d to a stim u lu s. A n e x a m p le of and lose their fear of them. However they th is is the re sp on se of m a ny you n g pheasa nts, ch ic ken s a nd tu rke y s never become accustomed to the unfa- to the sig ht of m o v in g o bje c ts o v erhe ad . W itho u t h av in g b e en in miliar shapes of predators, because these a ny w ay tau g ht to do so, they crouch dow n or show som e other form o f a la rm b e h av io r-a b e h av io r p at te rn th at c le a rly h a s to d o w ith birds are rare. d efen se a ga in st a p re d ator. H ow e v er, a fter a fe w su c h e x p erienc e s, their c rouc h in g re sp on se w a ne s : the y lo se th is genera l fea r of bird s or o bje c ts fl y in g o v erhe ad . In other w ord s, their sen sitiv it y to the 42


stim u li g radu a lly dec reases. T h is pro c ess, c a lled h abit u ation , is v er y u se fu l, b e c au se o b v io u sly if y ou n g bird s w ere to c rou c h d o w n e v er y tim e a n o th e r bird fl e w p a st th e y w o u ld b e lo sin g a g re at d e a l of tim e in ne e d le ss a la rm b eh av ior. D o e s th is m ea n th at c h ic k s, a s the y g row old er, g e t u s e d t o a ll b ird s fl y in g o v e rh e a d ? N o t at a ll, a nd th at is the su btle a nd fa sc in atin g th in g ab ou t h abit u ation . C h ic k s b e c om e h abit u ate d on ly to sh ap e s th at the y se e re p eate d ly-suc h a s son g bird s or e v en fa llin g le av e s. T ho se th at a re n e w o r st ra n ge t o th e m w ill st ill a la rm th e m . S in c e b ird s o f p re y a re m u c h le s s n u m e ro u s th a n non p re d ator y sp e c ie s , c h ic k s h av e lit t le c h a nc e to ge t u se d to them , a nd w hen a h aw k fl ie s o v erh e ad a c h ic k w ill c ro u c h , a lth o u g h it w ill p ay no attention to a flo c k of sp a rrow s. T he fac t th at the c h ic k h a s no w ay of k no w in g th at a h aw k is d a n gerou s, h av in g ne v er e x p erienc e d a n at tac k from one , m a k e s its c rou c h lo ok lik e a n in n ate re sp on se . A c t u a lly it is not . It is th e re su lt of a “gap � in the c h ic k ’s h abitu ation . H avin g lea rne d w h at sh ap e s a re not h a rm fu l, it c onfi nes its crouch in g to shap es w h ich cou ld still be h a rm fu l u ntil p ro v e d other w ise b y fa m ilia rit y.

T he ac tion of a ru n n in g c at or a d ro olin g d o g is p o sitive , som eth in g th at the a n im a l h as lea rne d to do. Slig htly pu z z lin g a re p o sitive ac tion s th at lo o k lik e n e g at iv e o n e s . W h at w o u ld w e s ay ab o u t a p ik e th at le a rn e d n ot to hu nt stic k le b ac k s? Po sitiv e or ne gativ e ? N a iv e y ou n g p ik e w ill often t r y to sn ap u p stic k le b ac k s , on ly to fi n d t h at t h e ra ise d sp in e s o f t h e sm a lle r fi sh p re v e nt t h e m fro m b e in g sw a llo w e d . A f t e r a L e a rn in g n o t t o c ro u c h is a n e gat iv e p ro c e ss . fe w su c h e x p erienc e s, p ik e sto p hu ntin g stic kT h e re a re o th e rs w h ic h a re ju st th e o p p o sit e , lebac k s. A lthou g h th is lo ok s lik e h abitu ation , it in w h ic h the a n im a l le a rn s to d o som e th in g-in is not . T he p ik e h a s not b e c om e u se d to stic kshort , to re sp ond to a stim u lu s to w h ic h it w a s lebac k s ; it h a s lea rne d the entire ly p o sitiv e fac t orig ina lly ind ifferent. T h is pro c ess w as m ade fath at sp ik y lit t le fi sh c a n not b e sw a llo w e d a nd m ou s by the resea rches of Iva n Petrov ich Pav lov, m ig h t a s w e ll b e av o id e d . T h e a n t i p re d at o r w ho w ou ld , for in stance, rin g a bell every tim e he d efen se s of m a ny sm a ll a n im a ls d e p end on th is gav e a d o g fo o d . A fter m a ny su c h e x p erienc e s, abilit y o f p re d ato rs to le a rn fro m e x p e rie n c e . the d o g w o u ld d ro o l in a ntic ip ation w hene v er T h is is t h e re a so n w h y m a n y in se c t s d isp lay the b e ll w a s ru n g . T he p oint , of c ou rse , is th at so -c a lle d w a rn in g c olors, bro ad c a stin g the fac t a d o g d o e s not norm a lly d ro ol at the rin g in g of th at the y a re either p oisonou s or d ista stefu l or a b e ll bu t c a n b e tau g ht to d o so . T h is le a rn in g m ere ly h a rd-she lle d : bird s le a rn to re je c t them p ro c e ss o c c u rs w id e ly in n at u re . B ird s of p re y o n sig ht a ft e r th e y h av e t rie d th e m . A ll th e se sho w it b y re t u rn in g re g u la rly to p lac e s w here e x a m p le s d iffer from h abit u ation : the a n im a ls the y h av e su c c e ssfu lly hu nte d . S o d o e s m y c at do not b e c om e m erely in sen sitive to the stim u li , w h ic h ru n s t o th e k it c h e n w h e n it h e a rs m e bu t p o sitiv e ly c h a n ge their re sp on se to them . sh a rp en in g the c a r v in g k n ife . 43


Instinct vs. Organs Learning The Sense

L ea rn in g by im itation , thou g h ra re a m on g a n im a ls , is still a noth er form of interac tin g w ith the env iron m ent . S om e th in g lik e it is fou nd in som e son g bird s th at lea rn to sin g prop erly on ly b y listen in g to others of their sp e c ie s. If y ou n g c h a ffi n c h e s a re ra ise d w ith o u t h e a rin g oth e r ch a ffi nche s sin g , the y do not de velop their norm a l son g ; a ll the y pro duc e is a k ind of “u n intellig ible” w a rble . B ut if, in their form ativ e w e ek s, the y c a n he a r the son g of e x p erienc e d m a le s , th e y d e v e lo p th e n o rm a l so n g o f th e sp e c ie s . S om e sp e c ie s of bird s p o sse ss th is g ift of son g im itation to a h ig h deg re e , the w orld ch a m pion p ro b ably b ein g the m y n a bird of Ind ia . A G erm a n c o lle a g u e of m ine d id a n a m u sin g ex p erim ent on th is su bjec t w ith bu llfi nches. H e h ad one you n g m a le ra ise d by a fem a le c a n a ry, a n d th is bird , su rro u n d e d b y o t h e r c a n a rie s , ac q u ire d their son g , im itatin g it so e x ac tly th at its son g c ou ld not b e d istin g u ishe d from th at o f a t r u e c a n a r y. L at e r, t h is b u llfi n c h m at e d w ith a fe m a le o f it s o w n sp e c ie s a n d th e p a ir ra ise d you n g together. Tw o m a le s of th is bro o d le a rne d the c a n a r y son g from their father a nd sa n g It p erfec tly w hen they w ere g row n up. O ne of the se w a s sent to a n av ia rist t w o m ile s aw ay a nd m ated there w ith a fem a le bu llfi nch . W hen , t w o y e a rs late r, o n e o f th e so n s o f th is p a ir, a g ra n d so n o f t h e o rig in a l m a le , w a s re t u rn e d t o m y c o lle a g u e , It re w a rd e d h im b y sin g in g lik e a c a n a r y to o — the son g tau g ht fou r y e a rs p re v iou sly to its g ra nd father! T he ac q u isition of m otor sk ills b y p rac tic e is a lso w id e sp re ad . A lthou g h , as w e h ave se en , bird s ne ed not lea rn 44

the basic p attern of fl ig ht , the y probably do not ac q u ire p e rfe c t sk ill w ith o u t p rac tic e . I m e ntione d a lre ad y th at y o u n g g u lls h av e to le a rn to la nd a ga in st the w ind . T h is is p ro b ably tru e of m a ny ’ bird s, a nd It se em s th at in genera l the a rt of la nd in g is d iffic u lt a nd h a s to b e lea rne d . M a ny y ou n g bird s e v en fi nd the fi rst sta ge s of d e sc ent d iffic u lt onc e a irb orne , the y fly h ig her a nd h ig her a nd m ay b e c a rrie d off in a stron g w ind , ge t lo st a nd p erish . A ll the se e x a m ple s of lea rn in g h ave t w o th in g s in c om m on : the beh av ior is not p erfe c t the fi rst tim e it is sho w n , a nd to im p ro v e it the a n im a l m u st ac q u ire e x p e rie n c e o f so m e k in d . T h e reason that the you n g ch ick s g radu a lly stop p ed crouch in g w as sim ply the ex p erienc e that nothin g d re ad fu l h ap p ene d .

Innate T he m o st c om p le x interac tion s w ith the env iron m ent pro bably o c c u r in m on k e y s a nd ap e s, a n d in o u r o w n sp e c ie s . H a rr y F. H a rlo w a n d h is c o w ork ers at th e U n iv ersit y of W isc on sin a re c a rry in g out fasc in atin g stud ie s of beh av ior d e v e lop m ent in rhe su s m on k e y s. W h ile , a s w e sh a ll se e p re se n t ly, t h e in n at e e q u ip m e n t o f m o st lo w er a n im a ls is re lativ e ly c om p le te a nd often effic ient from the sta rt , th at of H a rlo w ’s m o n k e y s t u rn e d o u t t o b e m u c h le s s e la b o rat e ’ rat h e r it c o n sist e d o f a s e t o f re lat iv e ly v a g u e , genera l u rge s a nd ne e d s, w h ic h h ad to b e d e v e lop e d by c ontinuou s interp lay w ith the env iron m ent . B a sic a m on g the se ne e d s is th at


for se c u rit y­­­— w h ic h a norm a l rhe su s m other p rov id e s ab ov e a ll b y a llow in g the baby to c lin g to her b o d y. In fa nts d e priv e d of th is a nd oth er e x p re ssion s of m oth erly c a re a re to o frig htene d to v ent u re ou t on a ny e x p lorator y e x c u rsion s a nd so fa il to ac q u ire the ab so lu te ly v ita l e x p erienc e of the ou tsid e w orld . T he sa m e d e p riv ation h a s no le ss d isa stro u s effe c ts on the in fa nts’ later so c ia l life : the y fa il to d e v e lop c o op erativ e b ond s w ith their c om p a n ion s, a nd e v en to m ate norm a lly, b e c om in g either v er y a g g re ssiv e or ind ifferent . Sim ila r th in g s h av e b e en fou nd in other m a m m a ls a s w e ll, su c h a s c ats , rats a nd go ats. T here c a n b e lit tle d o u bt th at m a ny of the se fi nd in gs ap ply likew ise to hu m a n in fa nts—in fac t, w e rely even m ore on e x p erienc e . Such is hu m a n n atu re th at w hen w e lo ok to o eagerly for one th in g w e m ay fa il to se e others. To o c onc entrate d a se a rc h for a ll k ind s of effe c ts of e x p erienc e m ay blind u s to the fac t th at in the m ajorit y of a n im a ls m u c h of the p ro g ra m m in g of the b eh av ior m ac h in e r y is d o n e int e rn a lly. E v e n w h e n b e h av io r is m o ld e d b y interp lay w ith the env iron m ent , th is m old in g m ea n s no m ore th a n a c h a n ge of a b eh av ior th at w a s a lread y fu nc tion in g , a nd m ay e v en h ave been fu nc tion in g fa irly w ell. For ex a m ple , w h ile you n g go slin gs d o le a rn to fo llo w the o bje c t to w h ic h the y a re fi rst e x p o se d , their v er y fi rst re sp on se is not Ju st ra nd om : the y w a lk— w h ic h is itse lf a c o ord in ate d m ov em ent of c on sid erable c om p le x it y, e v en thou g h it is not p erfe c t the fi rst tim e — a nd the y d o not follo w ju st a ny th in g , the y p refer o bje c ts th at m o v e , th at a re of a c erta in siz e ra n ge , a nd th at h av e c erta in other c h a rac teristic s. W e h av e a lso se en th at the fi rst fl ig ht of a pige on a nd the fi rst fl ig ht of a butterfly, w h ile p erh ap s not p erfe c t , a re at le a st e x trem e ly c om p e tent . W e a lso k no w th at the d isplay s of m a ny sp e c ie s of fi she s a nd bird s a re not lea rned ; the y d e v e lop norm a lly in a n im a ls th at h av e b e en ra ise d a lone , a nd e v en in tho se th at h av e h ad fo ster p a rents of other sp e c ie s.

Isolation We isolate some sticklebacks while they are still in the egg, and we never let them see another fish or any object of a similar size until they are fully mature and ready to breed. Then, and only then, do we show them another male stickleback in breed-

ing condition or a dummy with a red belly O u r k no w le d ge of th e se m at ters is still e x t re m e ly p atc hy. Ye t w e which simulates a breeding male; our isoa re b e g in n in g to se e th at on the one h a nd m o st a n im a ls a re fa irly lated fishes will attack it. w e ll p ro g ra m m e d intern a lly but th at on the other h a nd the y often re q u ire a va riet y of “adju stin g in struc tion s” from their env iron m ent in ord er to re ac h the rem a rk able effic ienc y the y sho w w hen ad u lt . It is go o d to e x p re ss one se lf c autiou sly here b e c au se a satisfac tory term inolo g y h a s not y e t b e en genera lly a g re e d on . Pa rtic u la r c a re h a s to b e e x e rc ise d in th e u se o f th e t e rm “in n at e ,” fo r th is t e rm h a s le d to m isu nd ersta nd in g s b e c au se d ifferent p e o p le at tac h d ifferent m e a n in g s to it . Su p p o se th at w e a re d isc u ssin g the fi g htin g b eh av ior of m a le th re e -sp ine d stic k le b ac k s in bre e d in g c ond ition . T he se fi sh , a s w e k now, attac k re d o bje c ts m ore th a n other o bje c ts. 45


Instinct vs. Learning

W e m a k e a n e x p erim ent to se e if th is b eh av ior is in n at e o r le a rn e d b y e x p e rie n c e : w e iso lat e s o m e st ic k le b ac k s w h ile t h e y a re st ill in t h e e g g , a nd w e ne v er le t them se e a nother fi sh or a ny o bje c t of a sim ila r siz e u ntil the y a re fu lly m atu re a nd ready to breed . T hen , a nd on ly then , d o w e sho w them a nother m a le stic k le b ac k in bre e d in g c ond ition or a du m m y w ith a re d b elly w h ic h sim u late s a bre e d in g m a le ; ou r iso late d fi she s w ill at tac k it .

then w e c a n p ro p erly c a ll th is in n ate , sinc e a s a n inte g rate d w ho le it re q u ire s no e x p erienc e . Ye t e v en so , the term c a n b e m isu nd ersto o d— w h ic h le ad s u s to a nother im p orta nt a sp e c t of th e p ro b le m . L e t u s o b se r v e a n e w ly h at c h e d

c h ic k a s it fi rst sta rts to fe e d . It w ill p e c k at the fi rst g ra in it se e s, bu t its a im w ill b e v er y p o or. In on ly a few d ay s, how ever, its a im w ill im prove m a rk e d ly. Is not th is lea rn in g— the re su lt of e xp erienc e , in w h ich a go o d p eck is rew a rded w ith a g ra in of c orn a nd a p o or one w ith noth in g ? It T h is m ay sou nd stra ig htforw a rd enou g h . Sinc e w o u ld c e rt a in ly se e m so , bu t th is c o n c lu sio n ou r fi she s, in their isolation , c ou ld not p o ssibly h a s b e en p ro v e d fa lse in a n in gen io u s e x p e rih av e le a rn e d to at t ac k c o m p e t ito rs , it w o u ld , m e nt in w h ic h e y e g la sse s w ith sp e c ia l le n se s seem their behav ior m u st be in nate. But to dem w e re fit t e d t o c h ic k s . T h e se le n se s m ad e t h e on strate th at c erta in lea rn in g pro c e sse s a re not g ra in s of c orn ap p e a r to b e h a lf a n inc h to one re q u ire d for a norm a l d e v e lopm ent is not rea lly sid e of w here the y re a lly w ere . O b e d iently the the sam e as to say that the behav ior is in nate. To ch ick s a im ed w here they thou g ht the g ra in w as. p rov e in n atene ss, w e m u st sho w th at no interT heir p eck s w ere p oor at fi rst, but as before, they p lay w ith the env iron m ent h a s b e en ne c e ssa r y im prov e d in ac c u rac y a s the c h ic k s g re w old er, a lthou g h th is ac c u rac y w as a lw ay s m isd ire c te d b y the g la sse s. T he c h ic k s ne v er got a ny g ra in at a ll, a nd the inc re a se d c onc entration of their p e c k s— at the w ron g ta rget— w as obv iou sly the resu lt of som eth in g other than lea rn in g by bein g at a ll. A nd ou r pro c edu re d id not fu lly elim in ate re w a rd e d w ith fo o d . W h at it ac t u a lly w a s w e a ll p o ssible effe c ts th at the env iron m ent m ig ht d o not y e t k no w. It m ay h av e b e en som e th in g h ave h ad . It c ou ld w ell be th at at a n ea rlier stage a s u ne x p e c te d a s the fac t th at the c h ic k s w ere the g ro w in g e y e s of the se stic k le b ac k s ne e d e d b e c om in g inc rea sin g ly stead y on their leg s a nd to be ex p o se d to lig ht in order to sta rt fu nc tionthu s c ou ld p e c k m ore ac c u rate ly. in g prop erly. A t a ny rate , th is h a s b e en fou nd to b e the c a se in the d e v e lop m ent of tad p ole s a nd W h ic he v er u se of the w ord “in n ate ” w e p refer, som e h ig her a n im a ls. T he sa m e m ig ht b e tru e w e st ill c a n p ro v e n o th in g ab o u t th e inte rn a l of stic k lebac k s to o . T herefore , if by “in n ate” w e p ro g ra m m in g o f a n a n im a l b y su b je c t in g it m ea n “prog ra m m ed c om pletely w ithout c ontrol t o e x t e rn a l t e st s . W e c a n iso lat e it , re a r it in b y the env iron m ent , “ then w e c a n not d e sc rib e d a rk ne ss, in silenc e , a nd a ll w e c a n show is th at the stick leback s’ attack behav ior as in nate as w e t h e s e t h in g s d o n o t in fl u e n c e d e v e lo p m e n t . have not investigated p o ssible env iron m enta l ef- T h is is ne gativ e e v id enc e , a n at tem p t to p ro v e fe c ts on such ea rlier ph ase s of the de velopm ent. som e th in g b y e lim in ation . It d o e s not d em onstrate th at the beh av iora l m ach inery do e s g row H o w e v e r, if w e m e a n b y “in n at e ” t h at a f u lly in t e rn a lly— le t a lo n e h o w . F o r re a l p ro o f, w e d e v e lop e d fi sh , onc e a ll its sen se s a re fu nc tionm u st u n ravel the g row th pro c e sse s them selve s. in g , sho w s c o ord in ate d a nd c om p le x b eh av ior T herefore , ju st as outside c ontrol c a n be prove d w it h o u t p rac t ic e , c o n d it io n in g o r im it at io n ,

“The action of a running cat or a drooling dog is positive, something that the animal has learned to do.”

46


on ly b y ra isin g a n im a ls u nd er v a rie d e x tern a l H ere, then , is a d irec t ex p erim enta l ind ic ation of c ond ition s, so intern a l c ontrol h as to be stud ie d a p a rtic u la r k ind of intern a l p ro g ra m m in g , for th rou g h interferin g w ith intern a l c ond ition s. the sk in pro g ra m s its sen sory nerv e s. H ow th is t a k e s p lac e is still u n k no w n , bu t the e v id enc e E x p e rie n c e o f t h e lat t e r k in d h av e a s y e t n o t th at it d o e s h ap p en is c le a r-a nd the p ro of d o e s b e en d one on a ny la rge sc a le , bu t one e x a m p le n ot re st on e lim in ation o f o u t sid e e ffe c t s , bu t is w orth m ention in g in som e d e ta il. If w e tic k le on rea l interferenc e w ith intern a l d e v e lop m ent the sk in on the bac k of a fro g , it w ill re sp ond by pro cesses. S o fa r, w e k now a lm o st noth in g about sc ratc h in g the tic k le d sp ot w ith a w e ll— a im e d th e n at u re o f int e rn a l c o nt ro l o f th e d e v e lo p m o v e m e n t o f it s le g . T ic k le it s b e lly, a n d t h e m e nt o f b e h av io r, a n d st ill fa r to o lit t le ab o u t fro g w ill sc rat c h it s b e lly. T h is is p o ssib le b e t h e e q u a lly c o m p lic at e d p ro b le m o f h o w it is c au se sen sor y n er v e s ru n n in g from e ac h p a rt a ffe c t e d b y e x t e rn a l e x p e rie n c e . S t u d e nt s o f of th e sk in to th e sp in a l c ord p ro v id e th e fro g le a rn in g a ll o v er the w orld a re te stin g the orie s w ith in form ation ab o u t th e sp ot w h e re it w a s of the w ay s in w h ich ex p erienc e ch a n ge s beh avstim u late d . N o w, if at a v er y e a rly st a ge of d e ior a nd a lso a re tr y in g h a rd to d isenta n g le the v e lopm ent— n a m e ly, b efore the nerv e s g row in g interna lly c ontrolled events. Yet, so intric ate a re o u t fro m t h e sp in a l c o rd h av e ac t u a lly m ad e the p ro c e sse s th at th is fie ld of re se a rc h , one of c o n t ac t w it h t h e sk in— w e e x c h a n g e a b it o f the m o st c h a llen g in g a nd m o st c ru c ia l for ou r b ac k sk in on a fro g w ith a bit of b e lly sk in , w e u nd ersta nd in g of b eh av ior, is still in its in fa nc y. w ill in d u e c o u rse se e so m e t h in g su r p risin g . A ft e r th e n e r v e s h av e h ad t im e t o m a k e c o n- W e h av e le a rn e d a fe w t h in g s . W e k n o w , fo r ne c tion b e t w e en the sk in a nd the sp in a l c ord , in st a n c e , t h at m a n y c o m p le x b e h a v io r p at th is p a rtic u la r fro g , if tic k le d on the b ac k , w ill t e rn s a re n e it h e r a ll int e rn a l n o r a ll e x t e rn a l sc ratc h its b e lly— a nd v ic e v ersa ! bu t a c om bin ation of the t w o , a s sho w n b y the w ay sq u irre ls c rac k h a z e lnu ts. A h a z e lnu t h a s T h is fa sc in at in g e x p e rim e nt a llo w s o n ly o n e a g ro o v e in its she ll, a nd a n e x p erienc e d sq u ire x p la n at io n , a n d a v e r y st a rt lin g o n e at t h at . re l w ill g ra sp the nu t in su c h a w ay th at it c a n To st a r t w it h , it sh o u ld b e st re s s e d t h at t h e g n aw at th is g ro ove , q u ic k ly de e p en in g it. T hen t w o p atc h e s o f sk in d e v e lo p e d n orm a lly e v e n it w ill t u rn the nu t a rou nd in its “ h a nd s, “ g iv e t h o u g h t ra n sp la nt e d . T h e p ie c e o f b ac k sk in it a q u ic k , h a rd bite a nd the nut w ill c rac k op en . g re w d a rk g re en a lth o u g h it w a s on th e w h ite T h is e x t re m e ly e f fi c ie nt p ro c e d u re c o nt ra st s belly, a nd the piec e of belly sk in g rew w h ite even stron g ly w ith th at of a you n g sq u irrel w h ich h as t h o u g h o n t h e b ac k-w h ic h p ro v e d t h at t h e re been raised on other k ind s of food and w h ich has w e re c h e m ic a l d if fe re n c e s in t h e m f ro m t h e h ad no o p p ort u n it y to p rac tic e m a n ip u latin g , b e g in n in g . T h e se c h e m ic a l d ifferenc e s ap p a rg n aw in g a nd c rac k in g . Tru e , it w ill sta rt in a s if e nt ly m ad e t h e m se lv e s k n o w n t o t h e n e r v e s , it w ere the m o st sk illfu l g n aw er in sq u irreldom . in e ffe c t say in g , “I a m a p ie c e o f b ac k sk in” o r It w ill g ra sp th e nu t , t u rn in g it o v e r a n d o v e r “I a m a p ie c e o f b e lly sk in ,” n o m at t e r w h e re a nd g n aw in g aw ay w ith g reat energ y, ju st a s a n the y w ere lo c ate d . In short , the fu nc tion of the e x p erien c e d sq u irre l w ill, a n d a fter a n ap p ro ner v e , u nd e term ine d at fi rst , w a s se t tle d onc e priate interv a l, it w ill try to c rac k the nut op en . a n d fo r a ll b y t h e c h e m ic a l n a t u re o f t h e b i H o w e v er, a ll the se efforts a re v er y ineffe c tiv e ; t of sk in into w h ich it h ad g row n , a nd not by the in ste ad of ho ld in g the nu t so th at it c a n g n aw lo c ation of th at bit of sk in . at the g ro ov e , it g n aw s a ll ov er the su rfac e , a nd 47


Instinct vs. Organs Learning The Sense

a s a re su lt its c rac k in g e fforts a re in v a in , a nd it h a s to sta rt o v er a ga in . In short , the sq u irre l is pro g ra m m e d intern a lly for m a n ip u latin g , for g n aw in g a nd for c rac k in g , bu t it m u st le a rn b y e x p erienc e ho w to d o the se th in g s w e ll. A n oth er e x a m p le of th e joint ac tion of in n ate abilit y a nd im provem ent by lea rn in g is prov ided b y th e so n g le a rn in g o f c h a f fi n c h e s . W e h av e se en th at isolate d ch a ffi nche s d e velop a k ind of w a rblin g son g w h ic h is v er y d ifferent from the norm a l son g of the sp e c ie s. Ye t th is son g d o e s sho w som e u n m ist a k able c h a rac teristic s— for in st a n c e a rat h e r c h a f fi n c h lik e rh y t h m . F u rther, w h ile it is a lso true th at such isolate d bird s c a n lea rn a v a riet y of son g s, the son g the y lea rn m o st re ad ily is th at of th eir o w n sp e c ie s. T h is m e a n s t h at a lt h o u g h t h e y le a r n , t h e t h in g s the y w ill lea rn b e st a re them selve s d eterm ine d b y intern a l p ro g ra m m in g . W h at is m o re , t h e se sp e c ifi c a bilit ie s a n d in c lin ation s to le a rn c h a n ge in th e c o u rse of a n a n im a l‘s life . M a ny th in g s a re le a rn e d o n ly at c e r t a in t im e s . A d u c k lin g o r a g o slin g is n o t at a ll tim e s e q u a lly “im p rintable .“ If d u c k lin g s 48

a re h atc he d a lone in a n inc u b ator a nd , in ste ad of b ein g sh o w n a m oth er or a su b stit u te so on after hatch in g , a re kept lo cked up for a few d ay s, the y h av e a ll bu t lo st the abilit y to b e c om e im p rinte d . T he tend enc y to fo llo w a m other a nd le a rn w h at sh e lo o k s lik e ap p e a rs so o n a f t e r h at c h in g , re ac h e s a p e a k in a fe w h o u rs a n d t h e n g ra d u a lly w a n e s . T h is ap p lie s t o o t h e r t h in g s a s w e ll it is p ro b a b le t h at m a n y b ird s h av e to ac q u ire th e fi ner sk ills of fl y in g in th e fi rst fe w m o nth s a f t e r fl e d g in g , a n d th at th is b e c o m e s m o re d if fi c u lt if th e y a re p re v e nt e d from p rac tic in g . D ig ger w a sp s e v en le a rn their la nd m a rk s in the fe w se c ond s it ta k e s them to m a ke their lo c a lity stud ies. In other w ord s, there a re “critic a l p eriod s” in the lives of an im a ls w hen they a re m ore ready to lea rn c erta in th in gs tha n they a re at other tim es. It is of c ou rse p a rt of ou r ta sk to fi nd out w h at d eterm ine s the on set a nd the end of su c h c ritic a l p erio d s. T he stud y of a n im a ls in their n atu ra l su rrou ndin g s h a s re v e a le d m a n y e x a m p le s o f t h e s e d e e p — ro o t e d d e t e rm in a nt s o f t h e re ad in e ss to le a rn . B u m ble b e e s th at a re ou t fora g in g for ne c ta r— y ield in g pla nts w ill, w hen the y h ap p en on a ne w one , m a k e a q u ic k lo c a lit y st u d y of it so th at th e y c a n fi nd it a ga in . B u t th e y d o not d o t h is w it h a ll p la n t s . S o m e , lik e fo x g lo v e s , h av e su c h la rge a nd c on sp ic u o u s flo w ers th at the y c a n b e se en a nd lo c ate d from a d ista nc e . It is on ly the none u no btru siv e one s w ith sm a ll blo ssom s th at p rom p t a b e e to m a k e a lo c a lit y st u d y. T he u sefu lne ss of th is is c le a r; bu t w h at determ ine s w hether or not the be e w ill “de c ide” t o le a rn is a n y th in g bu t c le a r. It w ill su r p rise n o b o d y th at a n ap e is m ore inte lligent th a n a rab bit . Sim ila rly, c ro w s, p a rrots, a nd ge e se a re m ore intelligent th a n h aw k s, g u lls, or ch ic k en s. T h e se d iffe re n c e s in o v e r-a ll le a rn in g a bilit y a nd genera l inte lligenc e o c c u r th rou g hou t the a n im a l k in g d o m . W h at is le ss w e ll k n o w n is th at there a re e qu a lly profou nd d ifferenc e s th at


d o not ne c e ssa rily d e p end on o v er-a ll inte lligenc e . M u rre s a re no m ore inte lligent th a n g u lls, a nd y e t the y a lw ay s le a rn to re c o g n iz e t h e ir o w n e g g s , w h ic h g u lls d o n o t . G u lls a re p o t e nt ia lly sm a r t enou g h to d o th is, a nd their eg g s a re d ifferent enou g h to p erm it it . W hy, then , do the y not do so ? T he a n sw er is th at the y h ave a nother w ay of lo c atin g their ne sts— b y le a rn in g the lay of the la nd m a rk s rou nd about them . P rov ide d it is in the rig ht plac e , a g u ll w ill ac c e pt a ny th in g th at lo ok s a ny th in g lik e a n eg g , e v en a p otato , a s its ow n . W hat strikes the natu ra list about these d ifferenc es bet w een sp ecies is th at e ac h sp e c ie s d e v e lo p s its b eh av ior in a w ay th at se em s b e st su ite d to its ne e d s. T he m u rre s h ave to lea rn to re c og n iz e their ow n eg g s b e c au se the y d o not bu ild ne sts, a nd their eg g s m ay roll ab out on the ro c k le d ge s. It is u sefu l to a bu m ble b e e to le a rn the lo c ation of a p la nt w ith sm a ll flo w ers th at c a n not b e se en from a d ista nc e . W h at w e le a rn from a ll th is is th at it is not on ly the c om p le te , fu lly d e v e lo p e d b eh av ior th at is effic ient bu t a lso the w ay it d e v e lo p s. T h is c on c lu sion , w h ic h is a s y e t n o m ore th a n tent ativ e a s fa r a s d e ta ils a re c onc erne d , is v er y o b v iou s w hen w e c on sid er the g ro ss d ifferenc e s b e t w e en sp e c ie s or b e t w e en b eh av ior p at tern s w ith in a sp e c ie s. It is c le a rly of g re at ad v a nt a ge to a bird to b e able to fl y w e ll th e fi rst tim e it t rie s , p a rtic u la rly if it ne sts on a c liff or h ig h u p in a tre e . T he p re senc e of nu m erou s effic ient p re d ators m a k e s th is a m u stO n the other h a nd it w ou ld b e a h a nd ic ap to a bird if its in n ate k n o w le d ge o f w h at c on stit u te d ac c e p t able fo o d w e re to o sp e c ia liz e d . B y t r y in g o u t a la rge v a rie t y o f t h in g s a n d le a rn in g b y e x p erien c e to c on c ent rate on fo o d th at is go o d for it a n d th at is at the sa m e tim e abu nd a nt , a p a rtic u la r sp e c ie s w ill m a n a ge to m a k e th e m o st o f d iffe re nt h abit at s a n d d iffe re nt se a so n s o f th e y e a r. B e h av ior d e v e lo p m ent therefore p o se s the sa m e p ro blem a s the fi n ishe d b e h av ior: w e m u st not on ly u n rav e l the m e c h a n ism s Ducks from chicks c o nt ro llin g d e v e lo p m e nt b u t w e m u st a lso in v e st ig at e in d e t a il Since young chicks of many kinds crouch how the d e v e lop m enta l c ontrol in e ac h sp e c ie s m e e ts the p e c u lia r in alarm when the silhouette of a hawk ne e d s of th at sp e c ie s. passes overhead but ignore the shapes of A nd w h at ab out ou r ow n sp e c ie s? O f c ou rse w e k now th at w e lea rn other harmless birds like ducks, behaviora g re at d e a l, bu t d o w e a lso h av e a b a sic , intern a lly p ro g ra m m e d ists concluded that there was an inborn re p ertoire ? T h is is e x trem ely d iffic u lt to d e c id e , for w e d o not w a nt ability to tell the difference between the to c a rr y ou t e x p erim ents on ou r fe llo w hu m a n s, a nd c erta in ly not the k ind of d ra stic e x p erim ents th at w ou ld b e re q u ire d . W e w ou ld short-necked predators and longer-necked, not a llo w a ny b o d y to ra ise a b ab y in iso lation . W e h av e th ere fore harmless species. to re ly on inc id enta l a nd ind ire c t e v id enc e . T h e in d ic at io n s a re t h at t h e b u lk o f h u m a n in t e rn a l p ro g ra m 49


Instinct vs. Learning

m in g su p p lie s u s w ith re lat iv e ly sim p le u n it s of b eh av ior in re sp on se to sim p le stim u li w ith m otor pattern s like eye blin k ing , yaw n ing , w eep in g a n d sm ilin g , th e b a sic p at te rn o f lo c o m o tion a nd su c h sim p le re sp on se s a s the fl ic k in g m o v e m e nt s b y w h ic h w e b r u sh a n in se c t o ff o u r sk in . In ad d it io n , w e p ro b ab ly h av e so m e k ind of intern a l p ro g ra m m in g at h ig her le v e ls, su c h a s th e sp e c ific re sp on siv en e ss in m en to c e rt a in c o m p le x st im u li su p p lie d b y w o m e n , a nd v ic e v ersa . W e sh o u ld a lso m e nt io n a g g re ssiv e b e h av io r a n d m o th e rly nu rsin g b e h av io r p at t e rn s . B u t in th e ab se n c e o f re a lly d e c isiv e e v id e n c e , w e h av e to b e v ery c autiou s ab out ou r c onc lu sion s . A n e x tra re a son for c aution is th at a m a m m alia n em br y o m ay u nd ergo e x tern a l in flu enc e s a nd gather e x p erienc e w h ile still in the w om b. It h a s b e e n sh o w n , fo r in st a n c e , t h at h u m a n b abie s sho w d ifferenc e s in c erta in le g re fle x e s ac c ord in g to the p o sition (he ad d o w n or he ad u p) in w h ic h the y h ave sp ent their pren ata l life . T h e ge n e ra l p ro b le m , th at o f “ n at u re o r nu rt u re ,” is o f su p re m e im p o r t a n c e sin c e is su e s of the g re ate st u rgenc y d e p end on its solu tion . To w h at e x te nt c a n w e m a n ip u late m a n‘s a g g re ssiv e n e ss t h ro u g h e d u c at io n a l m e a su re s , fo r e x a m p le ? To w h at e x t e nt c a n w e c o nt ro l m a n’s w illin g n e ss t o b e t au g ht ? W h at a b o u t

50

t h e v e r y t e c h n iq u e s o f t e ac h in g ? W it h q u e stion s lik e th e se u n a n sw e re d , it is n ot su r p risin g th at the d e v e lo p m ent of b e h av ior is b ein g st u d ie d inten se ly in o u r n e a re st re lativ e s , th e other prim ates. W e have a lready seen that m uch of the adu lt so c ia l beh av ior of h ig her m a m m a ls, p a rtic u la rly m on k e y s a n d ap e s , is p rofo u n d ly in flu enc e d b y the re lation s a n a n im a l h a s h ad w ith its m other w hen you n g . E x p erienc in g norm a l m otherly lo v e (th at is, the entire , intric ate tre at m ent a lo v in g m oth er b e sto w s on h er infa nt) is ne c e ssa r y for the d e v e lo p m ent of later so cia l behav ior of m a ny k ind s. C lin ic a l ev idence w ith hu m a n b e in g s sh o w s th at th is is t ru e o f ou r sp e c ie s a s w e ll. But clin ic a l ev idence c an never be as conv incin g as ex p erim ents, and m uch of ou r u nderstand in g of the developm ent of hu m a n behav ior w ill have to c om e from the stu d y of b eh av ior in a n im a ls. N or shou ld w e c on fi ne such stud ie s to ou r nea re st re lat iv e s-ju st a s in t h e m e d ic a l s c ie n c e s , w h ic h h av e lo n g sin c e re lie d o n e x p e rim e nt s on a w id e v a rie t y of c re at u re s , w e ne e d to ge t ou r fac ts from a s m a ny d ifferent sou rc e s a s w e c a n . A n d t h is ap p lic at io n o f o u r w o rk t o t h e u n d e rst a n d in g o f m a n m ay in th e e n d b e th e m o st im p orta nt ju stific ation of a n im a l behav ior st u d ie s e v en thou g h it is a se lfi sh one .


One animal less well endowed may even make use of a superior nose belonging to another. It is a common sight in the African savanna to see baboons and impalas traveling together, the impala profiting from the baboon‘s keen eyesight, the baboon from the impala‘s sense of smell.

51


The Sense Organs

What Can Animals Learn? Certain behavior patterns are as thoroughly inbred as any physical attribute, others are wholly acquired, but most are subtle combinations of the two. To understand why animals act the way they do, it is essential to separate the innate from the learned. Untold hours of painstaking scrutiny, in laboratory and field, are being spent to unravel that puzzle, often with surprising results.

52


53


Instinct vs. Learning

A Tin Maze, a turtle and a dish of water provide a simple answer to the question: can turtles, known for their limited intelligence, learn? The answer is yes, they can. Just as turtles in nature find their way around their streamside homes, this one eventually learned to ignore the dead ends Attempt 38

and waddle straight down the path to the water. However, it took 38 tries.

Attempt 1-37

Some lessons from the laboratory Many questions concerning the relationship between

growing older. Hess calls this “ the natural unfolding

instinct and learning are best answered in the labora-

of innate processes�-as opposed to behavior which

tory. The chick at the right, for instance, is part of

becomes more efficient as a result of experience or

an experiment devised by a University of Chicago

learning. Interestingly, even human babies develop in

psychologist, Eckhard H. Hess. His problem was to

part this way. In one experiment, identical twins were

determine whether baby chicks, which demonstrably

separated, one kept on flat surfaces while learning

improve their pecking accuracy as they grow, do so as a

to crawl, the other given extensive experience with

result of maturing in their neuromuscular equipment or

stairs. Later, when the child accustomed only to flat

whether they actually learn by trial and error. Contrary

surfaces was introduced to stairs for the first time, it

to Hess's expectation, the former hypothesis proved

was found to climb just as well as its twin.

true- the chicks improved simply because they were 54


Peck marks aimed at a simulated seed set in soft clay prove the point. The top two patterns were made three days apart by a chick without prisms, the bottom two by a chick with prisms. In each case aim improves with maturity, but after three days the chick with prisms still pecks to the right of the mark.

55


When practice makes perfect In an ingenious experiment to test learning processes

nuts instinctively, it is only by trial and error that they

through practice, Irenaus Eibl-Eibesfeldt of the Max

learn to do it efficiently. This learned skill at opening

Planck Institute in Germany raised squirrels in natural

nuts may be contrasted with the squirrel‘s urge to

surroundings but without any seeds or nuts to practice

hide them, which is entirely innate. This makes good

on until they were adult. He wanted to find out whether

sense, as EiblEibesfeldt points out, since squirrels

the simple and elegant way in which experienced

eat so many different kinds of nuts and fruit pits that

squirrels open hazelnuts was “ perhaps an inborn

no single method of opening them would work for all.

trait and whether what appeared to be learning was

However, should squirrels have to learn to hide nuts

actually maturation in disguise.� He quickly found that

by experience, they might not survive their first winter.

although squirrels recognize, manipulate and crack 56


First attempt to open a hazel nut is made by an A second try shows improvement. After opening adult squirrel which has never seen a nut before. several more nuts, the squirrel has learned to concenGnawing tenaciously, the squirrel at last succeeds trate on one particular part of the shell. The re sult is but leaves a ragged shell scarred by many false starts. neater than the first but still is very time-consuming.

Further improvement shows after more practice.

Triumph! The meat comes out in one piece. The

The squirrel starts at the soft end of the nut, gnaws squirrel has finally found the natural grooves that exconnecting furrows and breaks out a piece. Still it has ist in hazelnuts, chiseled them deeper and cracked not found the best way, but it is close.

the nut with almost no waste effort. This experiment proves that, whereas the urge to open a nut, to hold it and gnaw it is instinctive, combining these behavior patterns into a well coordinated attack on one particular kind of nut is an acquired skill.

57


The Sense Organs

Once bitten, twice shy Mimicry is most often considered from the point of

how this learning process takes place in the case of a

view of the mimic-how good is its disguise? One tends

southern toad. This toad’s normal diet is insects, and

to forget that mimicry, no matter how ingenious, will

its instinct is to snap up anything that wiggles like one.

not work at all if the predator lacks the intelligence to

This particular toad had seen neither a bumblebee nor

be fooled or does not care what it eats. In some lower

its stingless and quite palatable mimic. Out of this ex-

species of predators the choice of foods is automatic

perience came a useful lesson about bees, and though

from birth, but often a predator's tastes are acquired.

in the future it may be fooled by robber flies and miss

Part of an experiment conducted at the Archbold Bio-

a potential meal or two, its ability to learn serves it

logical Station in Florida by Lincoln and Jane Brower in

well, since the sting of a bumblebee can be extremely

the course of their investigation into mimicry, illustrate

serious for a toad.

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59


The Sense Organs

Training the trainable Add to an animal’s native intelligence the patient and

to working out the easy way of doing things, Thus they

persuasive hand of the trainer, and the results, as

are receptive to rewards and, for that matter, punish-

these pictures show, can be astounding, It is axiomatic

ments, such as the bump on the nose the rat at the

that training capitalize on an animal ‘s natural abilities,

left gets when it jumps at the wrong door. On the other

The bears above, no matter how clever and willing,

hand, rewards mean nothing to the big circus cats,

could never have been taught to ride the motorcycle

These carnivores must be psychologically dominated

had they not initially been able to hold its handlebars,

by their trainer, just as in nature they are dominated

This is equally true where mental processes are con-

by another cat-hence the trainer’s whip and pistol.

cerned. Both rats and bears are canny animals, used 60


1. To begin the experiment, a palata ble

dragonfly is danced on the end of a thread in front of a hungry southern toad.

2.

5.

With a gulp the toad seizes the bait, Now a bumblebee is dangled. Like the the wings and abdomen of which protrude. other ba its, it was purposely exha usted Toads only snap at moving insects. and cannot fly-but it still can sting.

3. Next the toad is offered a robber fly, a 6. And it does I The toad rises to the bait, 8. close mimic of the bumblebee but lacking the bumblebee’s capacity to sting.

Now a robber fly is offered. Again but this time it gets a VIOlent sting on its the toad refuses, taking the fly for a bee, showing the fly ‘s mimicry to be effective. tongue and spits out the bee .

4. The toad, which has as yet never eaten 7. When a second bumblebee is offered, 9. To prove the toad did not refuse beca a bumblebee, gobbles up the robber fly as quickly as it did the dragonfly.

the toad will not snap at it and ducks its head, having learned its lesson.

use it had grown wary of a ll food or was sated, another dragonfly is offered.

10. The toad downs it just as it did the

first dragonfl y. Demonstra bly still hungry, it now knows good from bad.

61


The Sense Organs

The apprentice hunters Like squirrels learning to open hazelnuts, .these adolescent lions are trying their best to bring down 'a large horned animal, in this case a brindled wildebeest. Just as soon as lion cubs can follow their mothers around, they watch her taking game. By 10 months, they are well practiced at the art of stalking, keeping downwind and carrying out the flanking maneuver so characteristic of lions. But for another year or so the actual capture and kill of game is left to their elders. Then, abruptly, young lions like the two-year-olds in these pictures find themselves out on their own. In this case the lioness, which has the wildebeest by the muzzle the way a cowboy grasps a steer, stalked her prey expertly, charged from about 10 yards and correctly went for the head, fending off the .horns with one paw. But though she clung like grim death, she lacked both the weight and the skill to throw her prey. Next time she will undoubtedly do better.

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Colophon Artist: Aaron Branch Course: Designing with Type III Section: GC 363_03 Semester: Spring 2011 Professor: Joani Spadaro Fonts: Kepler MM Roman, and Trade gothic (Bold Condensed No. 20, Condensed no. 18, light, and medium) Software: Adobe Illustrator, Indesign, and Photoshop Printed by Blurb.com

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Animal Behavior