page_title: Recent human evolution
section_title: Archaic admixture
hierarchical_section_title: Recent human evolution / Archaic admixture
caption_attribution_description: English: Reconstruction of Neanderthal woman (makeup by Morten Jacobsen)
context_page_description: Recent human evolution refers to evolutionary adaptation, sexual and natural selection, and genetic drift within Homo sapiens populations, since their separation and dispersal in the Middle Paleolithic about 50,000 years ago. Contrary to popular belief, not only are humans still evolving, their evolution since the dawn of agriculture is faster than ever before. It is possible that human culture—itself a selective force—has accelerated human evolution. With a sufficiently large data set and modern research methods, scientists can study the changes in the frequency of an allele occurring in a tiny subset of the population over a single lifetime, the shortest meaningful time scale in evolution. Comparing a given gene with that of other species enables geneticists to determine whether it is rapidly evolving in humans alone. For example, while human DNA is on average 98% identical to chimp DNA, the so-called Human Accelerated Region 1, involved in the development of the brain, is only 85% similar.
context_section_description: Genetic evidence suggests that a species dubbed Homo heidelbergensis is the last common ancestor of Neanderthals, Denisovans, and Homo sapiens. This common ancestor lived between 600,000 and 750,000 years ago in Africa. Some members of this species migrated into Europe and the Middle East and became the Neanderthals while another group moved further east and evolved into the Denisovans, named after the Denisovan Cave in Russia where the first known fossils of them were discovered. The ones who stayed behind in Africa eventually became anatomically modern humans. Migrations and geographical isolation notwithstanding, the three descendant groups of Homo heidelbergensis later met and interbred.
  DNA analysis reveals that modern-day Tibetans, Melanesians, and Australian Aboriginals carry about 3%-5% of Denisovan DNA. In addition, DNA analysis of Indonesians and Papua New Guineans indicates that Homo sapiens and Denisovans interbred as recently as between 15,000 and 30,000 years ago. Archeological research suggests that as prehistoric humans swept across Europe 45,000 years ago, Neanderthals went extinct. Even so, there is evidence of interbreeding between the two groups as humans expanded their presence in the continent. While prehistoric humans carried 3%-6% Neanderthal DNA, modern humans have only about 2%. This seems to suggest selection against Neanderthal ancestry. For example, the neighborhood of the gene FOXP2, affecting speech and language, shows no signs of Neanderthal inheritance whatsoever. Introgression of genetic variants acquired by Neanderthal admixture have different distributions in European and East Asians. In particular, East Asians inherited more Neanderthal DNA than Europeans.  This points to differences in selective pressures. Nevertheless, because East Asians, South Asians, and Europeans tend to have more or less comparable Neanderthal heritage, hybridization events occurred after humans had migrated out of Africa between the ancestors of Eurasians and Neanderthals. Alternatively, it points to the possibility of humans interbreeding with Neanderthals in at least two major separate occasions, one involving the ancestors of Eurasians and one of East Asians. Following the genome sequencing of three Vindija Neanderthals, a draft sequence of the Neanderthal genome was published and revealed that Neanderthals shared more alleles with Eurasian populations—such as French, Han Chinese, and Papua New Guinean—than with sub-Saharan African populations, such as Yoruba and San. According to the authors of 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. But gene flow did not go one way. The fact that some of the ancestors of modern humans in Europe migrated back into Africa means that modern Africans also carry some genetic materials from Neanderthals. In particular, Africans share 7.2% Neanderthal DNA with Europeans but only 2% with East Asians.
  Some climatic adaptations, such as high-altitude adaptation in humans, are thought to have been acquired by archaic admixture. An ethnic group known as the Sherpas from Nepal is believed to have inherited an allele called EPAS1, which allows them to breathe easily at high altitudes, from the Denisovans. A 2014 study reported that Neanderthal-derived variants found in East Asian populations showed clustering in functional groups related to immune and haematopoietic pathways, while European populations showed clustering in functional groups related to the lipid catabolic process. A 2017 study found correlation of Neanderthal admixture in modern European populations with traits such as skin tone, hair color, height, sleeping patterns, mood and smoking addiction. A 2020 study unveiled Neanderthal haplotypes, or alleles that tend to be inherited together, among Africans linked to immunity and ultraviolet sensitivity. The promotion of beneficial traits acquired from admixture is known as adaptive introgression.
caption: Reconstruction of a Neanderthal female.
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