Human societies are remarkably variable in terms of their size, complexity, social structure, marriage systems and norms. This diversity has sometimes been raised as an obstacle to taking an evolutionary approach to human behaviour. However, a substantial proportion of the variation between human societies might represent local adaptation to ecological conditions and would thus be very much amenable to evolutionary explanation. I review recent studies correlating inter-population differences in humans with ecological factors, specifically pathogen prevalence. Many questions remain unanswered, such as whether we correctly understand the causal pathways and what the mechanisms producing local adaptation are, but the strength of correlations between social and ecological parameters is striking.