Legend has it that when Plato defined humans as "featherless bipeds", his great rival Diogenes strode into the academy and threw down the metaphorical gauntlet of a plucked chicken. He argued that according to Plato's definition, the naked bird would have to be allowed into the hallowed halls of humanity. Hence, Plato adjusted his definition to read, "a featherless biped with broad flat nails". One cannot fault him for accuracy, but somehow Plato's definition does not seem to cut to the heart of what is human.
In the proceeding years, philosophers and scientists have striven to identify distinguishing human attributes. Many candidates have been proposed: rationality, self-consciousness, tools, language, art, morality and religion, to name but a few. However, the endeavour has proven more difficult than one might think. When careful comparisons are made with other animals, especially our closest evolutionary relatives - monkeys and apes - some of the bastions of human uniqueness seem somewhat fragile. In the words of Stephen Lea: "There is no doubt that the human species is unique, if only because every species is unique, but unless we know quite a lot about the other species of animal that share our world, we are likely to be gravely mistaken about the precise nature of human uniqueness."
For example, Kenneth Oakely posited in Man the Tool Maker that our ability to make tools was our defining attribute. Then Jane Goodall observed wild chimpanzees breaking off twigs, stripping them of leaves and bark and then using them to fish termites out of their mounds. On receiving Jane's excited telegram outlining her discovery, Louis Leakey made the famous remark: "Now we must redefine tool, redefine Man, or accept chimpanzees as human."
The response of many scholars was redefinition not acceptance. It has been argued that we are the only creatures to use tools to make tools and that we are the only creatures dependent on tools for our survival. (Although Gen Yamakoshi has found that when seasonal fruits are scarce, nuts hammered open with stones are an essential fallback food for the chimpanzees of Bossou.) The very concept of tool has been redefined in such a way as to exclude non-human examples. As Frans de Waal puts it: "Some scholars have emphasised that human technology is embedded in role complementarity, symbols, cooperative production and education. In their opinion, the 'tool' label is not deserved if some or all of these elements is missing, such as when a chimpanzee cracks nuts with rocks, or, I suspect when a farmer picks his teeth with a twig."
Similar resistance to comparative data is evident with regards to many aspects of human behaviour, such as language, art, culture, imitation and teaching. An intellectual battle is being waged, and terms such as these are being used by some scholars as boundary markers between humans and other animals. De Waal believes that we should adopt inclusive not exclusive definitions. "Narrow definitions neglect boundary phenomena and precursors, and they often mistake the tip of the iceberg for the whole," he argues.
De Waal has recently produced two books that eloquently and powerfully champion the comparative approach. The Ape and the Sushi Master primarily considers the fierce debate over whether non-human animals can be said to possess culture. The second is an edited volume, Tree of Origin, in which different aspects of monkey, ape and human behaviour are compared.
The comparative-evolutionary approach could not ask for a better champion than de Waal. He was trained as an ethologist in the tradition of Lorenz and Tinbergen. He is probably best known for his fascinating descriptions of the Machiavellian shenanigans within a large colony of chimpanzees at Arnhem Zoo in his homeland of Holland. But de Waal is also a highly original thinker and a wonderful communicator.
I must admit that initially I found the title of The Ape and the Sushi Master rather off-putting. However, I have come to love it. Not only is it reminiscent of one of the titles of Aesop's fables, but it also places proper emphasis on the contribution that Japanese scientists have made to the field of cultural primatology. In fact, it was the great Japanese primatologist Tetsuro Matsuzawa who provided the inspiration for the title.
He suggested that apes may learn cultural habits following the model of an apprentice sushi chief. For three years the apprentices follow and observe a master chef without receiving direct instruction. They are waiting for the day that they will be able to make their first sushi, which they apparently do with remarkable dexterity. In a similar vein, the best anecdotes of apparently complex imitation in apes that I have heard came from zoo staff who described what happened when their ape charges escaped from their cages. One incident involved a chimpanzee and the other an orangutan. In both cases the apes unravelled and turned on hoses, collected soap, bucket, mops and scrubbing brushes and proceeded to clean their cages. They had watched their keepers perform similar cleaning routines for many years and, when given the opportunity, they re-enacted the procedure.
The Ape and the Sushi Master is full of such anecdotes. Perhaps now and again there is a little too much reliance on anecdotal evidence. However, de Waal is writing for a popular audience, he writes like an angel, and at no point does the work become pedantic or dry. He is as interested in the culture of science as he is in the culture of other animals. The book is full of fascinating biographical details. I was pleasantly surprised to find that I enjoyed learning about the scientists as much as I did reading about their subjects of study. If I have any criticisms, it would be that the book is a little overlong. The last section in particular is rather superfluous and detracts somewhat from the main thesis.
Tree of Origin is a more technical book. It will not (and was not designed to) appeal to such a wide audience. Nevertheless, it is very well edited and all nine contributors successfully fulfil the mandate of writing in an accessible, jargon-free style. In fact, the contributors constitute some of the leading lights in evolutionary-comparative primatology and it is a treat to find examples of their work collected together in one volume.
Tree of Origin attempts "to understand human social evolution from the perspective of what we know about the social organisation, communication, learned habits, subsistence, reproduction, and cognition of other extant primates". Anne Pusey and Karen Strier consider how best to model social organisation in human and non-human primates. De Waal discusses the contribution that the little-known bonobo or pygmy chimpanzee might make to our understanding of the evolution of human behaviour. Unlike common chimpanzees, their society is female dominated and they are renowned for "making love not war". Craig Stanford describes the politics that surround hunting and meat eating in common chimpanzees and Richard Wrangham considers the contribution that cooking might have made to the nutrition of our early human ancestors. Richard Byrne and Robin Dunbar both discuss social intelligence and the evolution of large primate brains. Charles Snowdon discusses language and what we might learn from primate communication. Finally, William McGrew provides an analysis of the status of cultural primatology.
We are very closely related to living primates: the two species of chimpanzee are genetically closer to us than they are to the other great apes, gorillas and orang-utans. The evolutionary approach to human behaviour is gaining ground, not least because of a wider acceptance of findings in the field of behavioural genetics. It is time to stop erecting barriers between ourselves and other animals. The point of comparative primatology is not to trivialise how far humans have come, but to recognise that we can gain insights into what it is to be human by studying the behaviour of other species. I hope that de Waal's books will encourage people to look at primates with a new respect and as, in de Waal's words, "serious members of our extended family with their own resourcefulness and dignity".
Debbie Custance is lecturer in psychology, Goldsmiths College, University of London.
Tree of Origin: What Primate Behaviour can Tell us about Human Social Evolution
Editor - Frans de Waal
ISBN - 0 674 00460 4
Publisher - Harvard University Press
Price - £19.95
Pages - 311