This article explores how human mating and marriage systems are affected by conditions of ecology, by cultural practices, and by the interactions of these two forces. Given the great diversity in marriage rules and rules about association and sexual conduct across societies, it would be easy to throw up one's hands and regard these patterns as somehow 'purely cultural'. There are, however, often (sometimes non-obvious) influences of the distribution, abundance, and predictability of resources that shift the likelihood of success and persistence for different cultural systems. Thus, cultural and genetic changes over time seem to be inevitably linked, and marriage rules lie at the heart of this phenomenon. However, defining 'culture' in a way useful to hypothesis testing is difficult, and culture and genetics change in different ways.