The Hitchhiker's Guide to Altruism: Gene-Culture Coevolution, and the Internalization of Norms

The internalization of norms refers to the tendency of human beings to adopt social norms from parents (vertical transmission) or influential elders (oblique transmission). Authority rather than fitness-enhancing capacity accounts for the adoption of internalized norms. Suppose there is one genetic locus that controls whether or not an individual is capable of internalizing norms. We extend the seminal models of Cavalli-Sforza and Feldman (1981) to show that if adopting a norm is fitness enhancing, the allele for internalization can evolve to fixation. Moreover, even a small amount of oblique transmission in favor of the norm renders fixation virtually inevitable. We then add to the model a replicator dynamic (horizontal transmission of fitness-enhancing phenotypic traits), showing that the tendency of agents to switch from lower to higher-fitness norms enlarges the basin of attraction of the internalization allele. Finally, we use this framework to model analytically Herbert Simon's (1990) explanation of altruism. Simon suggested that altruistic norms, which are by definition fitness-reducing, could 'hitchhike' on the general tendency of the internalization of norms to be fitness-enhancing. We find that the altruistic phenotype can evolve only if there is a sufficient level of oblique transmission, even when there is a strong horizontal transmission process biased against the altruistic norm.