RICHARD WRANGHAM: I make my living studying chimpanzees and their behavior in Uganda. I'm really interested in looking at the question of human evolution from a behavioral perspective, and I find that working with chimps is provocative because of the evidence that 5 million, 6 million, maybe even 7 million years ago, the ancestor that gave rise to the Australopithecus, the group of apes that came out into the savannahs, was probably very much like a chimpanzee. Being with chimpanzees in the forests of Uganda, as with the forests anywhere else in Africa, is pretty much like going into a time machine and enables us to think about the basic principles that underlie behavior.

Although humans are enormously different from the apes, the extraordinary thing that has emerged over the last two or three decades — and this is becoming increasingly clear recently — is that in maybe three big ways in particular, humans are more ape-like in their social behavior than you would expect to occur by chance. Moreover, there's something about our relationship to the apes that has carried through in terms of our behavior. To take an example, there are only two mammals that we know of in the world in which males live in groups of their male relatives and occasionally make attacks on individuals in neighboring groups so brutally that they kill them. Those two mammals are humans and chimpanzees. This is very odd and it needs explanation.

EDGE: Why was this not noticed until the last generation or so?

WRANGHAM: Chimpanzees weren't studied at all in the wild until 1960. It took 14 years after that before people were seeing them at the edges of their ranges. It's just difficult to follow them all over the place. It was 1974 when the first brutal attacks were seen, and these led to the extinction of an entire chimpanzee community in Gombe. People monitored that under Jane Goodall's research direction. And then slowly over the years it's been realized that chimps will carry on or will kill individuals in other communities. So now we've had chimp killing going on not only in Gombe and at the site I work at, in Kibale in west Uganda, but chimps have also killed other chimps in Budongo in Uganda and in Mahale in Tanzania. It just takes time for these observations to accumulate.

EDGE: Will the chimps kill others in their own community?

WRANGHAM: Yes, occasionally there's a Julius Caesar-like assassination, which is, of course, really intriguing, because we've got these tremendously important coalitions that go on within chimpanzee communities that determine a male's ability to do what a male is desperately striving to do all the time, which is to become the alpha male. And the question that arises once you see that on occasion these coalitions can lead to what are essentially assassinations is, what makes them stable normally? How is it that you don't get constant erosion of confidence, such that you get one individual isolated and the others all forming coalitions against him. These killings are rare events, but we know a fair amount about them. The most important aspect underlying the similarity is the fact that you can have extraordinary imbalances of power. You can have three or four individuals all jointly attacking another one, which means that it's essentially safe for the attackers. So if they decide that they are in a coalition against a victim, they can dispatch him relatively safely. That means that any animal can do that, and there are other animals that do, although they don't live in groups with their own relatives in the same way as chimpanzees do. Hyenas and female lions are other examples of animals that engage in this type of activity.

We've got three things that are really striking about humans and the great apes in parallel. The violence that chimps and humans show is pretty much unique to those two species. Then you have the extraordinary degree of social tolerance in humans and bonobos, another ape that is equally closely related to humans. And then you have a remarkable degree of eroticism in bonobos compared to humans. These parallels are not easily explained and raise all sorts of provocative questions, given the fact that humans have so many differences from the other apes in terms of our ecology, our language, our intelligence — our millions of years of separation.