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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. [ABSTRACT FROM AUTHOR]

The authors reflect on protection of isolated societies in South America. They state government policies of Brazil and Peru, along with support by the United Nations, is to leave isolated societies alone and comments on problems with this strategy due to intermittent interaction with the outside world introducing diseases to the tribes. They recommend controlled contact with isolated tribes and the importance of sustained around-the-clock medical treatment and food.