Demographics of genetic admixture and expansion.

We explore the dynamics of genetic admixture and expansion, as well as language assimilation, through mathematical-demographic modeling. Our primary goal is to address the population-genetics 'paradox' wherein autosomes and allosomes present markedly different, if not contradictory, pictures of past migrations. We demonstrate that this paradox may find a purely demographic explanation, as single-sex and two-sex reproduction models exhibit markedly distinct dynamics. We illustrate that the three processes-allosomal expansion, autosomal admixture, and language assimilation-occur at significantly different modes, potentially explaining the varied outcomes of these processes upon the completion of ethnogenetic transitions. Our research offers valuable insights into the intricate interplay between demography, genetics, and social organization, providing implications for historical scenarios and enhancing our understanding of the long-term consequences of migration and social cohesion.