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This Dwindling Group Of Hunter-Gatherers Was Once The Most Populous Ethnic Group Of Humans In The Entire World

New genomic research on the Khoisan people of southern Africa reveals an unwritten story in our shared human history.

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The Khoisan people currently reside in southern Africa and maintain a hunter-gatherer lifestyle.

Stephan C. Schuster / Via science.psu.edu

Known for their "click" languages, they are a unique but dwindling ethnic group. Census counts suggest that there are about 100,000 Khoisan language speakers remaining.

Their numbers have been in decline ever since the “Bantu Expansion” around 3,000 years ago, when a population of subsistence farmers from West Africa made an eastward and southward expansion.

Jc86035 / Via commons.wikimedia.org

After this expansion and more recent colonial pressures, the largest remaining populations of Khoisan people currently reside in the Kalahari Desert.

Despite their dwindling numbers, they maintain the greatest genetic diversity of all human populations.

They also have the most ancient Y-chromosome and mitochondrial DNA lineages (two types of molecular clocks) of any human population on Earth.

High genetic diversity is normally associated with large population groups, so what’s the deal?

There are two possibilities: Khoisan people had either a large ancestral population, or lots of recent interbreeding. Stephan Schuster, Hie Lim Kim, and their colleagues used high-powered genomic testing to shed some light on the mystery.

Their new study analyzed the entire genome of five Khoisan individuals and compared their results to genomic information from other major human populations.

Stephan C. Schuster / Via science.psu.edu

Using this information, they were able to infer genetic heritage and population size for the different groups through hundreds of thousands of years of human history.

First: there was very little genetic evidence of interbreeding with other populations.

Stephan C. Schuster / Via science.psu.edu

Remarkably, two individuals in the study didn’t have even a shred of non-Khoisan genetic material. The researchers believe this rules out the interbreeding explanation.

Second: the Khoisan group appears to have been the first to split off from the rest of the other early human populations, around 150,000 years ago.

They are distinct not only from Asians and Europeans, but also from other Africans. This explains why they have such ancient DNA.

Third: the population size of all human groups in the study declined dramatically between 30,000-120,000 years ago, but the Khoisan population declined the least.

Hie Lim Kim et al (2014). Red annotations are my own. / Via nature.com

Many scientists believe that the cause of this decline was a dramatic global change in climate.

Because of that slower decline, Khoisans have been the most populous ethnic group throughout much of the last 120,000 years of human history.

Stephan C. Schuster / Via science.psu.edu

Though they have declined dramatically in very recent human history, the Khoisan people retain a genetic diversity that demonstrates their ancient dominance.

The team suggests that the same climate changes that negatively affected most human populations lead to more favorable conditions in the areas that the Khoisan population inhabited.

Most of Africa became much drier. But the Southern Khoisan region likely grew wetter. It's a lot easier to be a hunter-gatherer when things are growing and animals are thriving.

This all goes to show just how much of human history is beyond the reach of the written word. Science FTW!

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