Kin play limited role in chimp cooperation.

Male chimps collaborate in a variety of ways and, like people, often find partners outside of their immediate families for cooperative ventures, according to a long-term study of these creatures in the wild.

Kevin E. Langergraber of the University of Michigan in Ann Arbor and his colleagues spent a total of 20 months between 1999 and 2005 observing cooperative acts between pairs of adolescent and adult male chimps living in a large community in Uganda's Kibale National Park. Observed collaborative behavior among the 36 to 41 animals in the group at various times included hunting, sharing meat, mutual grooming, and defending territory against males from other groups.

The researchers also conducted extensive genetic analyses of each animal to determine which males were maternal or paternal siblings.

A majority of collaborating male-chimp pairs consisted of unrelated or distantly related individuals, the researchers report in an upcoming Proceedings of the National Academy of Sciences. When male chimps did cooperate with immediate family members, they almost always chose a maternal brother.--B.B.