Professor of Anthropology Richard W. Wrangham signed bananas and books last night at a reception promoting his latest book, Demonic Males: Apes and the Origins of Human Violence.

The signing gathered some 180 anthropology students and others at the Harvard Museum of Cultural and Natural History.

Wrangham, one of the world's leading authorities on primate behavior, spoke about his field research on the great apes of Uganda and the latest theories of human evolution, suggesting that human violence has an evolutionary origin.

The two species most closely related to humans, chimpanzees and bonobos, are respectively the most and least violent of all mammals.

Male chimpanzees have been observed to exhibit a pattern of deliberate, vicious violence against their own species.

Wrangham's examples included rape and a behavior he terms "lethal raiding."

Male chimpanzees habitually leave the main community in groups, in order to sit on the end of the community territory and call out into the neighboring range.

If several chimpanzees from the adjoining community reply, the first group does nothing. But if they hear only one call, they will converge on their victim and beat them to death.

Chimpanzees, Wrangham said, will not attack unless the danger to themselves is negligible, and they become wildly excited during the attack.

This is significant, Wrangham said, because "humans and chimpanzees are the only two mammals that launch raids into other groups with the intent to harm the other group," Wrangham said.

Wrangham suggested that lethal raiding might be related to hunting. In other words, nature selects in favor of the violent chimpanzee because that animal would be a more successful hunter. It might be possible, then, to substitute a rival of the same species for prey in the mind of the chimpanzee.

Next to the chimpanzee, Wrangham places its sibling species, the pacifistic bonobo.

Male bonobos have not been observed to engage in lethal raiding, and incidents of violence against females are few.

Wrangham suggests that several factors contribute to the bonobos' relative pacifism.

First of all, bonobos live in larger and more stable groups. There is a better balance of power, and males are less likely to try to challenge the leaders.