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To the Editors:

The exchange between Carl Degler and Clifford Geertz (NYR, April 3) illustrates the continuing confusions about the use of evolutionary models when trying to gain some insights into human nature. I would like to comment on some of the general issues, rather than entering into this particular debate. Evolution is useful for understanding history and only very incidentally for alerting us to possible insights into contemporary problems. The comparative or evolutionary study of human behavior should start with a rich understanding of the present; otherwise, the framing of the problems inevitably loses the distinctively human behaviors that are supposedly being investigated.

I believe the main points are more usefully illustrated by considering locomotion rather than sex because of the existence of a substantial fossil record and reliable comparative information. The only reason we know human beings are a special kind of biped is by studying human beings. It is not only that human locomotion cannot be predicted by investigating the behavior of any other mammal, but far more is known about human locomotion than about this behavior in other primates. If one is interested in the origins of our locomotor behavior, then fossils, comparative anatomy, and field studies are relevant. The footsteps found by Mary Leakey and her co-workers are 3.6 million years old—many hundreds of thousands of years older than the emergence of stone tools, large brains, or the ancient beings called Homo erectus. While the order: locomotion, stone tools, brain size is of historical interest, if I want to know how human beings walk, I would not waste a moment on the fragmentary fossils.

Comparative studies in which the behaviors of contemporary animals are used to reconstruct evolutionary sequences face much greater difficulties. This is well shown in the case of the sexual behaviors of the great apes (chimpanzee, gorilla, and orangutan). In orangutans the males mate whether or not the female is in estrus (heat). In gorillas there is a very brief estrous period, only two to four days, and the female initiates sexual behavior. In the common large chimpanzee most mating takes place in a long estrous period.¹ But recent study shows that the pygmy chimpanzee behavior is very different—copulation takes place throughout the cycle and homosexual behavior is common. In pygmy chimpanzees food sharing often accompanied sexual behavior and the ventral-ventral position (supposedly unique to humans) is frequent.² Although the large chimpanzee and pygmy chimpanzee are closely related (far closer than chimpanzee and human), it is not possible to predict the behavior of the pygmy form from that of the large species. If the pygmy form had been studied first, it would have been concluded that there was very little, if any, difference in the sexual behaviors of apes and human beings, and that sexual differences between humans and apes were not important in the origin of uniquely human behaviors.

I hasten to add that the issue is not one of right or wrong, but that the behaviors of apes have been studied only recently by very few people. A view commonly held for a long time (a major mistake of my own) was that the behaviors of the great apes were fairly similar, but it is now clear that each species is behaviorally distinctive in important ways. The point is that the human view of the nonhuman primates partially reflects careful observation and partially what human beings would like to believe. For example it was thought that the apes were peaceful, and this view was not only widely accepted but used as the basis for postulating peaceful human ancestors. The most recent studies, however, show that all the apes may be very aggressive, killing (and some even eating) members of their own species. The combination of modern field studies and carefully controlled laboratory investigations is reducing the uncertainty, but, as the study of the pygmy chimpanzee shows, there still may be major surprises, and the behavior of ancestors may be reconstructed in only the most general way.

The kind of logic “males should be selected for…” sounds so reasonable, but, stated in this way, the arguments would apply equally to all of the apes although their behaviors are very different. In my opinion, this kind of reasoning, unless supplemented by many facts and carefully qualified, is simply a barrier to analysis. It is defended by calling it a return to Darwinism—but Darwin marshaled the facts that were available to him and clearly understood that selection is a complex matter. Selection is important, but recently a variety of experiments has suggested that there may be biological evolution based on neutral genes and processes which were not known a few years ago. “Back to Darwin” may sound like a powerful slogan, but if all it means is paying no attention to molecular biology, it should just be labeled “Back.”

In recent years both the study of biological evolution and the study of behavior have become more complex and there is no generally accepted theory bringing the two into useful relations. A new synthetic theory is needed to replace the one formed more than forty years ago.

S.L. Washburn

Department of Anthropology

University of California

Berkeley, California