I remember firmly taking away the message from Jared Diamond's first major book ("The Third Chimpanzee: The Evolution and Future of the Human Animal"), the message that early human tribes were bound by kinship (kin selection) as the main motive for cooperation with the group, and that human tribes (like chimpanzee tribes) were antagonistic, so that the most likely outcome of a meeting between males of two different tribes would be a battle. Not, it now turns out, if that male is your brother or cousin. Because humans lived as foragers for 95% of our species’ history, Hill et al. analyzed co-residence patterns among 32 present-day foraging societies. They found that the members of a band are not highly related. Both young males and young females disperse to other groups (in Chimps, only females disperse). And, the emergence of a pair bonding between males and females apparently has allowed people to recognize their relatives, something chimps can do only to a limited extent. When family members disperse to other bands, they are recognized and neighboring bands are more likely to cooperate instead of fighting to the death as chimp groups do. The new view would be that cooperative behavior, as distinct from the fierce aggression between chimp groups, was the turning point that shaped human evolution.
Here is the Hill et al. abstract:
Contemporary humans exhibit spectacular biological success derived from cumulative culture and cooperation. The origins of these traits may be related to our ancestral group structure. Because humans lived as foragers for 95% of our species’ history, we analyzed co-residence patterns among 32 present-day foraging societies (total n = 5067 individuals, mean experienced band size = 28.2 adults). We found that hunter-gatherers display a unique social structure where (i) either sex may disperse or remain in their natal group, (ii) adult brothers and sisters often co-reside, and (iii) most individuals in residential groups are genetically unrelated. These patterns produce large interaction networks of unrelated adults and suggest that inclusive fitness cannot explain extensive cooperation in hunter-gatherer bands. However, large social networks may help to explain why humans evolved capacities for social learning that resulted in cumulative culture.A brief review of this work by Chapais asks the question:
...what “cognitive prerequisites” were necessary for social groups to act as individual units and coordinate their actions in relation to other units? Did hominins, for example, require a theory of mind (the attribution of mental states to others) and shared intentionality (the recognition that I and others act as a collective working toward the same goal) (10) to achieve that level of cooperation?