The role of cultural transmission in human demographic change: an age-structured model.

Human populations vary demographically with population sizes ranging from small groups of hunter-gatherers with less than fifty individuals to vast cities containing many millions. Here we investigate how the cultural transmission of traits affecting survival, fertility, or both can influence the birth rate, age structure, and asymptotic growth rate of a population. We show that the strong spread of such a trait can lead to a demographic transition, similar to that experienced in Europe in the late 19th and early 20th centuries, without using ecological or economic optimizing models. We also show that the spread of a cultural trait that increases fertility, but not survival, can cause demographic change similar to the 'Neolithic demographic transition': a period of increased population growth that is thought to have accompanied the transition from hunter-gatherer to agricultural lifestyles. We investigate the roles of vertical, oblique, and horizontal learning of such a trait in this transition and find that compared to vertical learning alone, horizontal and oblique learning can accelerate the trait's spread, lead to faster population growth, and increase its equilibrium frequency.