After Near Extinction, Humans Split Into Isolated Bands

Amitabh Avasthi
for National Geographic News
April 24, 2008

After nearly going extinct 150,000 years ago, humankind split into small groups—living in isolation for nearly a hundred thousand years before "reuniting" and migrating out of Africa, a new gene study says.

At one point our species may have been down to as few as 2,000 individuals, probably due to climate change—a longstanding theory bolstered by the new findings.

The research fills a gap in our understanding of what was happening in Africa before humans first left the continent.

"The assumption has always been that the original population [in sub-Saharan Africa] was very small but probably a single population," said Spencer Wells, head of the Genographic Project, which oversaw the study.

"Turns out, that is not the case."

(The National Geographic Society owns National Geographic News and funds the Genographic Project.)

The study appears in the current issue of the American Journal of Human Genetics.

Separate Ways

Around 200,000 years ago, modern humans emerged as a distinct species. All people alive today can trace their ancestry back to these humans, according to previous studies.

By the time the first great migrations out of Africa began, around 60,000 years ago, humanity had split into distinct populations with unique genetic lineages.

So what happened between 200,000 years ago and 60,000 years ago?

To find out, Wells and his colleagues analyzed 624 complete genomes of mitochondrial DNA—which is passed down from mothers—from various indigenous populations across sub-Saharan Africa. A genome is a person's complete set of DNA (quick overview of human genetics).

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