Michael Tomasello, a psychologist at the Max Planck Institute for Evolutionary Anthropology in Germany, said the survey provided a strong foundation for the view that cooperative behavior, as distinct from the fierce aggression between chimp groups, was the turning point that shaped human evolution. If kin selection was much weaker than thought, Dr. Tomasello said, “then other factors like reciprocity and safeguarding one’s reputation have to be stronger to make cooperation work.”

The finding corroborates an influential new view of early human origins advanced by Bernard Chapais, a primatologist at the University of Montreal, in his book “Primeval Kinship” (2008). Dr. Chapais showed how a simple development, the emergence of a pair bond between male and female, would have allowed people to recognize their relatives, something chimps can do only to a limited extent. When family members dispersed to other bands, they would be recognized and neighboring bands would cooperate instead of fighting to the death as chimp groups do.

In chimpanzee societies, males stay where they are born and females disperse at puberty to neighboring groups, thus avoiding incest. The males, with many male relatives in their group, have a strong interest in cooperating within the group because they are defending both their own children and those of their brothers and other relatives.

Human hunter-gatherer societies have been assumed to follow much the same pattern, with female dispersal being the general, though not universal, rule and with members of bands therefore being closely related to one another. But Dr. Hill and Dr. Walker find that though it is the daughters who move in many hunter-gatherer societies, the sons leave the home community in many others. In fact, the human pattern of residency is so variable that it counts as a pattern in itself, one that the researchers say is not known for any species of ape or monkey. Dr. Chapais calls this social pattern “bilocality.”

Modern humans have lived as hunter-gatherers for more than 90 percent of their existence as a species. If living hunter-gatherers are typical of ancient ones, the new data about their social pattern has considerable bearing on early human evolution.