Why cultural distance can promote - or impede - group-beneficial outcomes.

Quantifying the distance between cultural groups has received substantial recent interest. A key innovation, borrowed from population genetics, is the calculation of cultural F_ST (CF_ST) statistics on datasets of human culture. Measuring the variance between groups as a fraction of total variance, F_ST is theoretically important in additive models of cooperation. Consistent with this, recent empirical work has confirmed that high values of pairwise CF_ST (measuring cultural distance) strongly predict unwillingness to cooperate with strangers in coordination vignettes. As applications for CF_ST increase, however, there is greater need to understand its meaning in naturalistic situations beyond additive cooperation. Focusing on games with both positive and negative frequency dependence and high-diversity, mixed equilibria, we derive a simple relationship between F_ST and the evolution of group-beneficial traits across a broad spectrum of social interactions. Contrary to standard assumptions, this model shows why F_ST can have both positive and negative marginal effects on the spread of group-beneficial traits under certain realistic conditions. These results provide broader theoretical direction for empirical applications of CF_ST in the evolutionary study of culture.