Genetic Contributions from Archaic Humans and their Effects on Human Fitness

Comparisons of DNA from archaic and modern humans show that modern and archaic humans interbred, and in some cases received an evolutionary advantage from doing so. This process, adaptive introgression (AI), may lead to a faster rate of adaptation than is predicted from models with mutation and selection alone. Within the last couple of years, a series of studies have identified regions of the genome that are likely examples of AI. One clear example of AI involves the EPAS1 (HIF-2α) gene that had the most striking signature of positive selection in Tibetans, and the selected haplotype at this selected locus was most likely derived from an archaic human population (Denisovan) that had interbred with the ancestral Tibetan population. Other examples of AI are found in genes involved in immune function, metabolism and skin and hair pigmentation, suggesting that the selective agents are different pathogens, diets and temperatures, respectively. Here, we examine known examples of AI to discover new statistics that can specifically differentiate between introgression and adaptive introgression, and we use simulations to investigate the false positive rate of these statistics under null models that include introgression in the absence of selection