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Humans not just “big-brained apes,” researcher says

Aug. 22, 2007
Courtesy PNAS
and World Science staff
Updated Aug. 24

In dis­cus­sions on an­i­mal in­tel­li­gence, it’s fash­ion­a­ble to play up an­i­mals’ smarts and their si­m­i­lar­i­ties to hu­mans. And many stud­ies pro­vide fod­der for such think­ing.

But a new study, re­assess­ing much past re­search, of­fers a dif­fer­ent per­spec­tive: it ar­gues that key hu­man-ani­mal dif­fer­ences are of­ten over­looked. Hu­mans are more than just “big-brained apes,” as Charles Dar­win called them in 1871, wrote the au­thor, psy­chol­o­gist Da­vid Pre­mack of the Un­ivers­ity of Penn­syl­va­nia in Phil­a­del­phia, Penn.

Many stud­ies have ex­am­ined ape in­tel­li­gence. In this im­age, the chimp "Jes­sie" re­moves a blind­fold from a train­er who al­so has the key to a box con­tain­ing a ba­nana. Re­search­ers say this shows Jes­sie grasps the con­cept of "seeing": she real­izes that if she takes off the blind­fold, the train­er can open the box. While such stud­ies of­ten play up apes' sim­i­lar­i­ties to hu­mans, a psy­chol­ogist says they of­ten over­look the great dif­fer­ences: for in­stance, an­i­mal ac­tions usu­al­ly cen­ter on nar­row ob­jec­tives like food or sex. (Im­age cour­te­sy Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces)

In try­ing to change such con­cep­tions, Pre­mack is swim­ming against a tide of re­search that has found some­times sur­pris­ing cog­ni­tive abil­i­ties in an­i­mals, ca­pa­ci­ties once thought un­ique to hu­mans.

A study pub­lished last Ju­ly, for in­s­tance, found that even some ro­dents can re­mem­ber the “what, where and when” of events in their lives, an abil­ity some­times cit­ed as key to con­scious­ness. And find­ings made pub­lic just this week sug­gested rhe­sus monk­eys use “baby talk” with in­fants, though sur­pri­singly, not their own.

Pre­mack did­n’t chal­lenge the find­ings of past stud­ies. But he ar­gued that they of­ten fo­cus on an­i­mal-hu­man si­m­i­lar­i­ties—strik­ing us re­peat­edly with ex­amp­les of how animals are “so like us”—while gloss­ing over the vast realms of act­i­vity where they’re real­ly quite un­like us. That leads to the false idea that an­i­mals have hu­man-like abil­i­ties, he said.

Fur­ther con­fu­sion has aris­en be­cause hu­man brains do have si­m­i­lar­i­ties in struc­ture to oth­er mam­mals’, added Pre­mack, whose pa­per ap­peared in this week’s early on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces. For such rea­sons, most neu­ro­sci­en­tists agreed with Dar­win un­til re­cently.

Only since the late 1990s has re­search chal­lenged that no­tion, by re­veal­ing mi­cro­scop­ic fea­tures unique to hu­man brains, Pre­mack wrote. These stud­ies have found “en­hanced wir­ing, and forms of con­nec­ti­vity among nerve cells not found in any an­i­mal.”

One such find­ing, he added, in­volved a new­found type of neu­ron, or brain cell, that’s far more nu­mer­ous and larg­er in hu­mans than in any of their ape rel­a­tives. Called von Eco­no­mo neu­rons, these cells are par­tic­u­larly prev­a­lent in brain re­gions deal­ing with so­cial emo­tions such as em­pa­thy, guilt and em­bar­rass­ment, Pre­mack wrote.

In a crit­i­cal anal­y­sis of past lit­er­a­ture, Pre­mack ex­am­ined claims of si­m­i­lar­ity be­tween an­i­mals and hu­mans in sev­er­al dif­fer­ent ar­eas, in­clud­ing teach­ing, de­cep­tion, mem­o­ry, and lan­guage. In all cases, he ar­gued, the si­m­i­lar­i­ties are small and the dif­fer­ences large. 

A ma­jor dif­fer­ence is that an­i­mal be­hav­iors ap­pear to be mainly adapta­t­ions fo­cused on a sin­gle goal such as food-seeking, he wrote, where­as hu­man be­hav­iors have an in­fi­nite num­ber of goals. Such dis­par­i­ties are con­sist­ent with the ob­served dif­fer­ences in brain struc­ture; the chal­lenge is to un­der­stand the func­tion of these cell­u­lar-level dif­fer­ences, he wrote.

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In discussions about animal intelligence, it’s fashionable to play up animals’ smarts and their similarities to humans. And many studies provide fodder for such views. But a newly published paper examining past research offers a different perspective, arguing that important differences are often overlooked. Humans are more than just “big-brained apes,” as Charles Darwin called them in 1871, wrote the author, psychologist David Premack of the University of Pennsylvania. In trying to change such conceptions, Premack is swimming against a tide of research that has found sometimes surprising cognitive abilities in animals, capacities once thought unique to humans. A study published last July, for example, found that even some lowly rodents can remember the “what, where and when” of events in their lives, an ability sometimes cited as key to consciousness. Premack didn’t challenge the findings of past studies, but noted that they often focus on animal-human similarities, leading to the false idea that animals have human-like abilities. Further confusion has arisen because human brains do in fact have superficial similarities in structure to other mammals’, added Premack, whose paper is published in this week’s early online edition of the research journal pnas. For such reasons, most neuroscientists agreed with Darwin well into the 1980s. Only the past several years of research have challenged that notion, by revealing microscopic differences between human and animal brains, he explained. These studies have revealed “enhanced wiring, and forms of connectivity among nerve cells not found in any animal.” One such finding, he added, involved a newfound type of neuron, or brain cell, that’s far more numerous and larger in humans than in any of their ape relatives. Called von Economo neurons, these cells are particularly prevalent in brain regions dealing with social emotions such as empathy, guilt and embarassment, Premack wrote. In a critical analysis of past literature, Premack examined claims of similarity between animals and humans in several different areas, including teaching, deception, memory, and language. In all cases, he argued, the similarities are small and the differences large. A major difference is that animal behaviors appear to be mainly adaptations focused on a single goal such as food-seeking, he wrote, whereas human behaviors have an infinite number of goals. Such disparities are consistent with the observed differences in brain structure; the challenge is to understand the function of these cellular-level differences, he wrote.