History and Geographic Distribution
See also: Human evolutionary genetics#Modern humansA 10-year study published in 2009 analyzed the patterns of variation at 1,327 DNA markers of 121 African populations, 4 African American populations, and 60 non-African populations. The research showed that there is more human genetic diversity in Africa than anywhere else on Earth. The genetic structure of Africans was traced to 14 ancestral population clusters and the ancestral origin of humans was determined to probably be located in southern Africa, near the border of Namibia and South Africa.
Human genetic diversity decreases in native populations with migratory distance from Africa and this is thought to be the result of bottlenecks during human migration, which are events that temporarily reduce population size. It has been shown that variations in skull measurements decrease with distance from Africa at the same rate as the decrease in genetic diversity. These data support the Out of Africa theory over the multiregional origin of modern humans hypothesis. The aforementioned April 2009 study identifies the likely origin of modern human migration as being in southwestern Africa, near the coastal border of Namibia and Angola, and the exit point out of Africa as being in East Africa.
The recent African origin of modern humans is the mainstream model describing the origin and early dispersal of anatomically modern humans, Homo sapiens sapiens. The theory is known popularly as the (Recent) Out-of-Africa model. The hypothesis originated in the 19th century, with Darwin's Descent of Man, but remained speculative until the 1980s when it was corroborated based on a study of present-day mitochondrial DNA, combined with evidence based on physical anthropology of archaic specimens. According to a study done in 2000 on Y chromosome sequence variation, human Y-chromosomes trace ancestry to Africa and the descendants of the derived lineage left Africa and eventually they were replaced by archaic human Y-chromosomes in Eurasia. The study also shows that minority of contemporary East Africans and Khoisan represent the descendants of the most ancestral patrilineages of anatomically modern humans that left Africa between 35,000 and 89,000 years ago.
According to both genetic and fossil evidence, archaic Homo sapiens evolved to anatomically modern humans solely in Africa, between 200,000 and 100,000 years ago, with members of one branch leaving Africa by 60,000 years ago and over time replacing earlier human populations such as Neanderthals and Homo erectus. According to this theory, around the above time frame, one of the African subpopulations went through a process of speciation when gene flow was restricted between African and Eurasian human populations.
Read more about this topic: Human Genetic Variation
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“The history of progress is written in the blood of men and women who have dared to espouse an unpopular cause, as, for instance, the black man’s right to his body, or woman’s right to her soul.”
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“There is the illusion of time, which is very deep; who has disposed of it? Mor come to the conviction that what seems the succession of thought is only the distribution of wholes into causal series.”
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