Contextualizing Population Genetic Models of Sex-Biased Migration and Admixture

Modeling of sex-biased migration or admixture in human history often uses sex itself as the factor which controls the probability that any particular individual migrates. This modeling strategy aims to unite work across a large range of times and putative causes, from Neanderthal archaic introgression to the consequences of colonialism, relying on the assumption that two equally sex-biased events should leave signals in the genome drawn from the same distribution. We apply a contextualist view of sex to highlight the possible effects of intrasexual variation, and use simulations to demonstrate that demographically identical migration events can leave distinguishable patterns of ancestry in the genome if individuals within a sex are not exchangeable. Using this, we argue that modeling intrasexual variation can be an important factor for capturing the signals of sex-biased migration.