Recent human evolution
Recent human evolution refers to evolutionary adaptation and selection and genetic drift within anatomically modern human populations, since their separation and dispersal in the Middle Paleolithic. 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 H. sapiens have been essentially isolated for tens of thousands of years prior to the early modern Age of Discovery. Combined with archaic admixture this has resulted in significant genetic variation, which in some instances has been shown to be the result of directional selection taking place over the past 15,000 years, i.e. significantly later than possible archaic admixture events. Selection pressures were especially severe for populations affected by the Last Glacial Maximum in Eurasia, and for sedentary farming populations since the Neolithic.
Adaptations have also been found in modern populations living in extreme climatic conditions such as the Arctic and the Tibetan Plateau, as well as immunological adaptations such as resistance against brain disease in populations practicing mortuary cannibalism.
Some climatic adaptations, such as high-altitude adaptation in humans, are thought to have been acquired by archaic admixture. Introgression of genetic variants acquired by Neanderthal admixture have different distributions in European and East Asians, reflecting differences in recent selective pressures. 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.
Physiological or phenotypical changes have been traced to Upper Paleolithic mutations, such as the East Asian variant of the EDAR gene, dated to c. 35,000 years ago.
Recent divergence of Eurasian lineages was sped up significantly during the Last Glacial Maximum, the Mesolithic and the Neolithic, due to increased selection pressures and founder effects associated with migration. Alleles predictive of light skin have been found in Neanderthals, but the alleles for light skin in Europeans and East Asians, associated with, KITLG and ASIP, are (as of 2012) thought to have not been acquired by archaic admixture but recent mutations since the LGM. Phenotypes associated with the "white" or "Caucasian" populations of Western Eurasian stock emerge during the LGM, from about 19,000 years ago. The light skin pigmentation characteristic of modern Europeans is estimated to have spread across Europe in a "selective sweep" during the Mesolithic (19 to 11 ka). The associated TYRP1 SLC24A5 and SLC45A2 alleles emerge around 19 ka, still during the LGM, most likely in the Caucasus. The HERC2 variation for blue eyes first appears around 14 ka in Italy and the Caucasus.
Inuit adaptation to high-fat diet and cold climate has been traced to a mutation dated the Last Glacial Maximum (20,000 years ago). Average cranial capacity in modern human populations varies in the range of 1,200 to 1,450 cm3 (adult male averages). Larger cranial volume is associated with climatic region, the largest averages being found in populations of Siberia and the Arctic. Both Neanderthal and EEMH had somewhat larger cranial volumes on average than modern Europeans, suggesting the relaxation of selection pressures for larger brain volume after the end of the LGM.
Evolutionary adaptations have sped up significantly, at an estimated 100-fold pace compared to the Paleolithic, since the beginning of the Holocene, primarily in the farming populations of Eurasia. Hawks et al. (2007) have tied this effect to new selection pressures arising from the new diets, new modes of habitation, and immunological pressures related to the domestication of animals.
A recent adaptation has been proposed for the Austronesian Sama-Bajau in the form of an enlarged spleen which provides a larger amount of oxygen-rich red blood cells during, developed under selection pressures associated with subsisting on freediving over the past thousand years or so.
In modern historical times, since industrialization, some trends have been observed: for instance, menopause is evolving to occur later. Other reported trends appear to include lengthening of the human reproductive period and reduction in cholesterol levels, blood glucose and blood pressure in some populations.
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