Our ancestors picked up one of the particularly virulent strains of the HPV retrovirus that causes genital warts and cervical cancer when they had sex with Neanderthals. But, the genes that modern human received into its gene pool via Neanderthal hybrid individuals also enhanced the selective fitness of non-African modern humans in their new non-African environment in some important respects including immunity genes. In contrast, many other genes that we received from Neanderthals impaired selective fitness in modern humans, and were quickly purged from the modern human gene pool via natural selection.
Neanderthals (who were light pigmented relative to the Cro-Magnon modern humans that they encountered as a result of adaptation to their more northerly range) also provided some of the pigmentation genes now found in modern humans (although many of the pigmentation genes in Northern Europeans evolved independently and convergently in modern humans). Another kind of modern human with whom we admixed, the Denisovans, appear to have been a source of high altitude adaptations that are common in Tibetans and other Himalayan peoples and appear to have provided a different and additional set of novel immunity related genes.
Neanderthals (who were light pigmented relative to the Cro-Magnon modern humans that they encountered as a result of adaptation to their more northerly range) also provided some of the pigmentation genes now found in modern humans (although many of the pigmentation genes in Northern Europeans evolved independently and convergently in modern humans). Another kind of modern human with whom we admixed, the Denisovans, appear to have been a source of high altitude adaptations that are common in Tibetans and other Himalayan peoples and appear to have provided a different and additional set of novel immunity related genes.
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