Gene-Culture Coinheritance of a Behavioral Trait.

Many physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems and their interaction in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive. We then use this equation to investigate whether a genetically maladaptive phenotype can evolve under dual transmission. We examine the special case of altruism using an illustrative model and show that cultural selection can overcome genetic selection when the variance in culture is sufficiently high with respect to genes. We also show that the presence of cultural transmission can modify genetic selection itself, making genetic selection more favorable to a trait than under purely genetic inheritance. Last, we consider the effect of different timescales of genetic and cultural transmission. We discuss the implications of our results for understanding the evolution of important coinherited behaviors, including how our framework can be used to generate quantitative estimates of selection pressures required for a genetically maladaptive trait to evolve.