Science

Jim__

(14,074 posts) Mon Sep 23, 2019, 11:41 AM Sep 2019

Modern humans: One species, many origins

World map with land area resized to represent modern human genetic diversity and colour representing Neanderthal plus Denisovan ancestry. As can be seen, contributions from other populations to the Homo sapiens gene pool are small and unevenly distributed. Africa is disproportionately large because the great human genetic diversity - and hence the roots of humanity - are found here. Credit: James Cheshire/Mark G. Thomas

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In a paper published in Nature Ecology and Evolution, a group of researchers argues that our evolutionary past must be understood as the outcome of dynamic changes in connectivity, or gene flow, between early humans scattered across Africa. Viewing past human populations as a succession of discrete branches on an evolutionary tree may be misleading, they said, because it reduces the human story to a series of "splitting times" which may be illusory.

According to archaeologist Dr. Eleanor Scerri and geneticists Dr. Lounès Chikhi and Professor Mark Thomas, the quest for a single original location for modern humans is a wild goose chase. "People like us began to appear sometime between 500,000 and 300,000 years ago," says Dr. Scerri, group leader of the Pan-African Evolution Research Group at the Max Planck Institute for the Science of Human History and lead author of the study. "That is something in the order of 8000 generations, a long time for early people to move around and explore a big space. Their movements, patterns of mixing and genetic exchanges, are what gave rise to us."

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"The genetics of contemporary humans are very clear. The greatest genetic diversity is found in Africans," explains Prof. Thomas of University College London. "The old theory that we descend from regional populations spread across the Old World over the last million years or so is not supported by genetics data. Sure, non-Africans today have some ancestry from Neanderthals, and some have appreciable ancestry from the recently discovered Denisovans. And maybe other, as yet undiscovered ancient hominin groups also interbred with us, Homo sapiens. But none of this changes the fact that more than 90 percent of the ancestry of everybody in the world lies in Africa over the last 100,000 years."

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