Neanderthal-human Interbreeding Hypothesis
Any hypothesis about the reproductive potential of Neanderthals and humans must take into account data collected from the nuclear and mtDNA of both species. Humans and Neanderthals share a small percentage of nuclear DNA, but they do not share the same type of mtDNA. The mtDNA recovered from Neanderthal fossils contains sequences not found in present-day humans. How can we reconcile the data from studies of nuclear and mtDNA extracted from Neanderthal fossils and humans?
Neanderthals have contributed approximately 1-4% of the genomes of non-African modern humans, although a modern human who lived about 40,000 years ago has been found to have between 6-9% Neanderthal DNA (Fu et al 2015). The evidence we have of Neanderthal-modern human interbreeding sheds light on the expansion of modern humans out of Africa. These new discoveries refute many previous hypotheses in which anatomically modern humans replaced archaic hominins, like Neanderthals, without any interbreeding. However, even with some interbreeding between modern humans and now-extinct hominins, most of our genome still derives from Africa. Neanderthals could not have contributed to modern African peoples’ genomes because Neanderthals evolved and lived exclusively in Eurasia and therefore could not have bred with the humans living in Africa at that time.