Culture and the evolution of human cooperation

Abstract

The scale of human cooperation is an evolutionary puzzle. All of the available evidence suggests that the societies of our Pliocene ancestors were like those of other social primates, and this means that human psychology has changed in ways that support larger, more cooperative societies that characterize modern humans. In this paper, we argue that cultural adaptation is a key factor in these changes. Over the last million years or so, people evolved the ability to learn from each other, creating the possibility of cumulative, cultural evolution. Rapid cultural adaptation also leads to persistent differences between local social groups, and then competition between groups leads to the spread of behaviours that enhance their competitive ability. Then, in such culturally evolved cooperative social environments, natural selection within groups favoured genes that gave rise to new, more pro-social motives. Moral systems enforced by systems of sanctions and rewards increased the reproductive success of individuals who functioned well in such environments, and this in turn led to the evolution of other regarding motives like empathy and social emotions like shame.

Figure 1.

An equilibrium behaviour in a 16 × 16 array of populations linked by stepping stone migration on a torus is shown. There are three binary traits. Each combination of traits is evolutionarily stable when common, and all basins of attraction are the same. Populations are initialized at random. The vector of frequencies at evolutionary equilibrium is plotted as the RGB colour resulting from that mix of red, green and blue. (a) When migration rates are greater than or equal to selection coefficients (m ≥ s) all groups have the same behaviour at equilibrium. (b) When migration rates are somewhat less than to selection coefficients (2m = s) simple clines often persist at evolutionary equilibrium. (c) When migration rates are much less than to selection coefficients (10m = s) complex patterns of small scale variation often persist at evolutionary equilibrium.