Genetic ancestry, as well as facial characteristics, may play an important part in who we select as mates, according to an analysis from UC San Francisco, Microsoft Research, Harvard, UC Berkeley and Tel Aviv University

Researchers used population genomics and quantitative social sciences to gauge the relatedness of parents in a study of asthma in Mexican and Puerto Rican children. They found that the parents tended to choose partners with a similar mix of ancestry to their own, a phenomenon known as assortative mating. In the case of Mexicans, that meant having a similar proportion of mostly European and Native American ancestry, with some genomic heritage from Africa. For Puerto Ricans, that meant having similar amounts of European and African ancestry, with some Native American. The average mix was similar enough to make the couples equivalent to between third and fourth cousins, a degree of closeness that may have implications for the perpetuation of some genetic diseases but also could have health benefits. A study done in Iceland, for example, found that the most fertile couples were about as closely related as fourth cousins.