Vertical and oblique cultural transmission fluctuating in time and in space.

Evolutionary models for a cultural trait under vertical and oblique cultural transmission are analyzed. For a dichotomous trait, both the fitnesses of the variants and their rates of transmission are allowed to vary. In one class of models, transmission fluctuates cyclically together with fitnesses, and conditions are derived for a cultural polymorphism. A second class of models has transmission and selection fluctuating randomly with possible covariance between them. A third class of models involves two populations with migration between them and with transmission rates and fitnesses different in the two populations. Numerical analysis leads to qualitative conditions on the transmission rates and fitnesses that allow protected polymorphisms. With symmetric migration analytical conditions for protected polymorphism are derived.