25 Apr 2008

Study Suggests: Humans Nearly Became Extinct 70,000 Years Ago

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AP:

Human beings may have had a brush with extinction 70,000 years ago, an extensive genetic study suggests. The human population at that time was reduced to small isolated groups in Africa, apparently because of drought, according to an analysis released Thursday.

The report notes that a separate study by researchers at Stanford University estimated the number of early humans may have shrunk as low as 2,000 before numbers began to expand again in the early Stone Age.

“This study illustrates the extraordinary power of genetics to reveal insights into some of the key events in our species’ history,” Spencer Wells, National Geographic Society explorer in residence, said in a statement. “Tiny bands of early humans, forced apart by harsh environmental conditions, coming back from the brink to reunite and populate the world. Truly an epic drama, written in our DNA.”

Wells is director of the Genographic Project, launched in 2005 to study anthropology using genetics. The report was published in the American Journal of Human Genetics.

Previous studies using mitochondrial DNA — which is passed down through mothers — have traced modern humans to a single “mitochondrial Eve,” who lived in Africa about 200,000 years ago.

The migrations of humans out of Africa to populate the rest of the world appear to have begun about 60,000 years ago, but little has been known about humans between Eve and that dispersal.

The new study looks at the mitochondrial DNA of the Khoi and San people in South Africa which appear to have diverged from other people between 90,000 and 150,000 years ago.

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The BBC reports the study’s conclusion that mankind nearly split into two separate species at the same time.

Ancient humans started down the path of evolving into two separate species before merging back into a single population, a genetic study suggests.

The genetic split in Africa resulted in distinct populations that lived in isolation for as much as 100,000 years, the scientists say.

This could have been caused by arid conditions driving a wedge between humans in eastern and southern Africa.

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Behar et al., The Dawn of Human Matrilineal Diversity, The American Journal of Human Genetics (2008), doi:10.1016/j.ajhg.2008.04.002

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