Archaic human admixture with modern humans

The archaic human admixture with modern humans is thought to have been taken place through interbreeding of modern humans with Neanderthals, Denisovans, and/or possibly other archaic humans over the course of human history. Neanderthal-derived DNA accounts for an estimated 1–4% of the Eurasian genome, but it is significantly absent or uncommon in the genome of most Sub-Saharan African people. In Oceanian and Southeast Asian populations, there is a relative increase of Denisovan-derived DNA. An estimated 4–6% of the Melanesian genome is derived from Denisovans. Recent noncomparative DNA analyses—as no specimens have been discovered—suggest that African populations have a genetic contribution from a now-extinct archaic African hominin population.

Some researchers have expressed doubts about the recent admixture events. Ancient subpopulation structure ancestral to modern humans, Neanderthals, Denisovans, and other possible archaic humans has been proposed as an alternative explanation for the observed genetic similarities.

Through whole-genome sequencing, a 2010 draft sequence of the Neanderthal genome revealed that Neanderthals shared more alleles with Eurasian populations (e.g. French, Han Chinese, and Papua New Guinean) than with Sub-Saharan African populations (e.g. Yoruba and San). According to the study, the observed excess of genetic similarity is best explained by recent gene flow from Neanderthals to modern humans after the migration out of Africa. The proportion of Neanderthal-derived ancestry was estimated to be 1–4% of the Eurasian genome. In 2013, the same team of researchers revised the proportion to an estimated 1.5–2.1%. They also found that the Neanderthal component in non-African modern humans was more related to the Mezmaiskaya Neanderthal (Caucasus) than to the Altai Neanderthal (Siberia) or the Vindija Neanderthals (Croatia). Analyzing the genomes of Europeans and East Asians, it has been found that about 20% of the Neanderthal genome is still present in the modern human population.

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