How obedience of marriage rules may counteract genetic drift.

Marriage rules are a common component of many human societies. Since these rules, translated into mating patterns, would imply inbreeding, the question arises as to their long-term population genetic effects. We show by simulation that continuous unilateral or bilateral cross-cousin mating, reflecting the most common form of prescribed marriage, increases homozygosity but at the same time slows down considerably the loss of gene diversity due to genetic drift. For X-chromosomal genes, this effect is more pronounced if marriage, translated into mating, is matrilateral rather than patrilateral. Although the maintenance of gene diversity, in principle, could have conferred a selective advantage to the initiation of marriage rules, the mechanisms driving such a move are difficult to perceive. We therefore conclude that the possible preservation of gene diversity through marriage rule-induced inbreeding is a by-product, not the source, of a cultural invention that instead rested on foresight and strategic thinking.