Recent human evolution

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 has been proposed that human culture acts as a selective force in human evolution and has accelerated it; however, this is disputed. 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 chimpanzee DNA, the so-called Human Accelerated Region 1 (HAR1), involved in the development of the brain, is only 85% similar. Following the peopling of Africa some 130,000 years ago, and the recent Out-of-Africa expansion some 70,000 to 50,000 years ago, some sub-populations of Homo sapiens have been geographically isolated for tens of thousands of years prior to the early modern Age of Discovery. Combined with archaic admixture, this has resulted in relatively significant genetic variation. Selection pressures were especially severe for populations affected by the Last Glacial Maximum (LGM) in Eurasia, and for sedentary farming populations since the Neolithic, or New Stone Age. Single nucleotide polymorphisms (SNP, pronounced 'snip'), or mutations of a single genetic code "letter" in an allele that spread across a population, in functional parts of the genome can potentially modify virtually any conceivable trait, from height and eye color to susceptibility to diabetes and schizophrenia. While approximately 2% of the human genome codes for proteins and a slightly larger fraction is involved in gene regulation, the remainder has no known function. If the environment remains stable, the beneficial mutations will spread throughout the local population over many generations until it becomes a dominant trait. An extremely beneficial allele could become ubiquitous in a population in as little as a few centuries whereas those that are less advantageous typically take millennia. Human traits that emerged recently include the ability to free-dive for long periods of time, adaptations for living in high altitudes where oxygen concentrations are low, resistance to contagious diseases (such as malaria), light skin, blue eyes, lactase persistence (or the ability to digest milk after weaning), lower blood pressure and cholesterol levels, retention of the median artery, reduced prevalence of Alzheimer's disease, lower susceptibility to diabetes, genetic longevity, shrinking brain sizes, and changes in the timing of menarche and menopause.

Archaic admixture

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, likely in either Europe or Africa. Members of this species migrated throughout Europe, the Middle East, and Africa and became the Neanderthals in Western Asia and Europe while another group moved further east and evolved into the Denisovans, named after the Denisova Cave in Russia where the first known fossils of them were discovered. In Africa, members of this group eventually became anatomically modern humans. Migrations and geographical isolation notwithstanding, the three descendant groups of Homo heidelbergensis later met and interbred.

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