Fitness Enhancing Archaic Genes May Have Much Wider Distribution

For the most part, genetic traces of admixture between Denisovans and modern humans are found in people with Papuan or Australian Aboriginal descent.

But, select fitness enhancing genes, such as one related to the distribution of body fat on a person, match a gene found in Denisovans, have a much wider distribution.  This gene is found in Native Americans and mainland Asians which have little or no trace Denisovan ancestry otherwise and is particularly adaptive to arctic and high altitude conditions.

While other sources of these gene are possible (e.g. independent evolution of the same gene more than once), a source in archaic hominins seems likely.  If a gene has strong fitness enhancing effects, it isn't uncommon for it to reach fixation or at least significant proportions in a population, even if genes that are selectively neutral are almost sure to disappear through genetic drift in the same circumstances.