EDGE: How long have you been doing field work? How did you get started?

WRANGHAM: I've been studying chimps on and off for over 30 years. I began working at Jane Goodall's site at Gombe, which is the archetypal site and represents to many people what the chimpanzee is. In 1984 I moved to Uganda and started work on a forest chimpanzee population, and began thinking particularly about cultural variation, about the kinds of behavioral traditions that vary between the two sites that I had come to know best. I then used this as a vehicle for trying to understand variations in social behavior among chimpanzees.

One of the lovely things that's going on now is the discovery that in East Africa we have a series of behaviors that characterize the chimps that are different from the behaviors that we see in extreme West Africa — in Christophe Boesch's site in the Tai forest in the Ivory Coast, for example, and Bossou. We're seeing chimps in the east that are relatively fragmented in their groups, that have relatively little sexual activity, that have few female-female alliances, that have extreme male dominance over females — and all of these things are different in the west. In the most stable groups in the west, the females form alliances, the males are much more respectful of females, and there is much less violence in the community in general. There's very much less infanticide, and there are much less severe forms of territoriality. This is exciting, because it means that we can dissect the chimpanzee species and ask, where are the ecological influences and what effects are they having? And what does this mean in terms of trying to reconstruct the kind of chimpanzee that gave rise to us seven million years ago?

The answers are becoming clearer. In my field work I am trying to understand what it is about the ecology that leads to differences in behavior. A real key that has been given extraordinarily little attention is the fact that in some populations, the apes are able to walk and feed at the same time. In others they're not, because there's no food for them as they're walking. This sounds like an extraordinarily trivial difference, but it seems to be enormously important, because if you can walk and feed at the same time, then you can stay in a group with your friends and relations without additional members causing an increased intensity of feeding competition. On the other hand, if you are walking without feeding between the key food patches, then every time an additional chimp comes along and joins your party, the effect is that feeding competition is intensified in these food patches. And there is no melioration when you're moving between food patches. The long-term effect of this is that it fragments the parties, and it's the fragmented nature of these parties of chimps that don't have ability to walk and feed at the same time that underlie all of these social differences.

EDGE: What questions are you asking yourself today?

WRANGHAM: There are two really fascinating things about human evolution that we have yet to really fully come to grips with. One is the evolution of cooking. Whenever cooking happened, it must have had absolutely monstrous effects on us, because cooking enormously increases the quality of the food we eat, and it enormously increases the range of food items that we can eat. We all know that food quality and food abundance are key variables in understanding animal ecology. But the amazing thing is that although at the moment there is no conventional wisdom that says when cooking evolved, social anthropology and all sorts of conventional wisdom say that humans are the animals that cook. We distinguish ourselves from the rest of the world because they eat raw stuff and we eat cooked stuff. The best anthropology can do at the moment is to say that maybe sometime around 250 or 300 thousand years ago cooking really got going, because there's archeological evidence of earth ovens.

This is fine, but long before earth ovens came along we must have learned to cook. And you would think that cooking would be associated with things like evidence in your body of the food being easier to digest, such as smaller teeth, or maybe a reduction in the size of the rib cage as the size of the stomach gets smaller, or maybe the jaw getting smaller. And there's only one time in human evolution that all that happens; that is, 1.9 million years ago with the evolution of the genus Homo. It's there we must look for evidence that cooking was adopted.

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