Toward a theory for the evolution of cultural communication: coevolution of signal transmission and reception.

A haploid sexual two-locus model of gene-culture coevolution is examined, in which a dichotomous phenotype subject to natural selection is transmitted vertically with probabilities dependent on the chosen parent's genotype and phenotype and the offspring's genotype. Stability conditions for the genetically monomorphic corner equilibria are obtained. In a specialization of this general model, one locus controls the transmission and the other controls the reception of adaptive information. The corner and edge equilibria of this doubly coevolutionary model are fully analyzed, and conditions for transmission and reception to coevolve are derived in terms of the efficiency of vertical transmission, the selective advantage gained from possessing the information, the costs of transmission and reception, and the recombination fraction between the two loci. Possible applications of the model are to the evolution of semantic alarm calls in vervet monkeys and the phonetic aspects of human language. In a third model with diploid genetics, we consider the initial increase of cultural transmission from a mutation-selection balance in which the adaptive phenotype is the consequence of a dominant gene at one locus. A second gene controls the transmission of the phenotype in such a way that a new mutant at this second locus permits learning of the adaptive phenotype from a parent who has it. This new mutant cannot increase when rare.