CULTURAL RELATEDNESS UNDER OBLIQUE AND HORIZONTAL TRANSMISSION RULES

The concept of genetic relatedness is central to the sociobiological theory of kinship altruism. Genes which code for altruistic acts toward closely related genetic kin can overcome selection pressures favoring self-interested behavior. But genetic relatedness declines rapidly as kinship becomes more distant, thereby restricting genetically-based altruism to very close kin. This paper extends these notions to cultural relatedness, arguing that oblique and horizontal transmission can yield high levels of cultural relatedness in larger groups. A mathematical model of cultural transmission is proposed, and equilibria for several special cases are investigated. For all models, the equilibrium level of relatedness is critically dependent on the influence of exogenous sources. In models with equal influence of nonparents, the level of relatedness varies inversely with group size. On the other hand, when nonparental influence is concentrated on a single individual, the level of relatedness does not vary with group size.