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.

It is widely assumed that modern hunter-gatherer societies lived until very recently in isolation from food-producing societies and states and practiced neither cultivation, pastoralism, nor trade. This paper brings together data suggesting a very different model of middle to late Holocene hunter-gatherer economy. It is argued that such foraging groups were heavily dependent upon both trade with food-producing populations and part-time cultivation or pastoralism. Recent publications on a number of hunter-gather societies establish that the symbiosis and desultory food production observed among them today are neither recent nor anomalous but represent an economy practiced by most hunter-gatherers for many hundreds, if not thousands, of years. Psychological and political reasons for Westerners' attachment to the myth of the "Savage Other" are discussed.

Human adaptation depends on the integration of slow life history, complex production skills, and extensive sociality. Refining and testing models of the evolution of human life history and cultural learning benefit from increasingly accurate measurement of knowledge, skills, and rates of production with age. We pursue this goal by inferring hunters’ increases and declines of skill from approximately 23,000 hunting records generated by more than 1800 individuals at 40 locations. The data reveal an average age of peak productivity between 30 and 35 years of age, although high skill is maintained throughout much of adulthood. In addition, there is substantial variation both among individuals and sites. Within study sites, variation among individuals depends more on heterogeneity in rates of decline than in rates of increase. This analysis sharpens questions about the coevolution of human life history and cultural adaptation.

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