Ancestral homeland of modern humans in Botswana, study finds

Katie Ramirez
October 29, 2019

An worldwide team of researchers analyzed the mitochondrial genomes of more than 1,200 people from southern Africa, including Khoisan individuals who continue to live as hunter-gatherers, to trace back the oldest maternal lineage.

"We are in a medical research institute here at the Garvan Institute and we work on many different diseases, trying to understand the genetic link that puts us at risk to many different types of diseases".

While it has always been known anatomically modern humans - homo sapiens sapiens - originated in Africa, scientists have until now been unable to pinpoint the precise location of our species' birthplace.

The study located Botswana, Namibia and Zimbabwe as humanity's point of origin. "What we hadn't known until this study is where exactly this homeland was". According to the study, the earliest modern people resided here for about 70,000 years before certain groups branched out to other locations.

The first migrants ventured north-east, followed by a second wave of migrants who travelled south-west and a third population remained in the homeland until today. This region held Africa's largest lake system Lake Makgadikgadi.

"What we hadn't known until now is where exactly this homeland was", said Vanessa Hayes, a geneticist at the Garvan Institute of Medical Research in Sydney, Australia, and the lead author of the study. This would have created a vast wetland region, ideal to sustain life.

One major branch of this tree is known as L3, which arose around the time anatomically modern humans left Africa, and is today shared by all non-African populations, and some but not all within Africa.

But if it was so ideal, why did our ancestors begin to explore other places between 130,000 and 110,000 years ago, first heading northeast and later southwest from the ancestral home? "In contrast to the northeasterly migrants, the southwesterly explorers appear to flourish, experiencing steady population growth".

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It also sparked the development of their genetic, ethnic and cultural diversity, the researchers said.

To the southwest, our ancestors had to adapt to foraging and using resources found in a marine environment, and it appears they did so successfully, Hayes said.

Professor Axel Timmermann, a climate scientist at Pusan National University in South Korea, said: 'These shifts in climate would have opened green, vegetated corridors, first 130,000 years ago to the north east, and then around 110,000 years ago to the south west, allowing our earliest ancestors to migrate away from the homeland for the first time'.

An global team of researchers took DNA samples from 200 Khoesan people, an ethnic group known to carry a high proportion of a branch of DNA known as L0, living in modern day South Africa and Namibia.

There is also a pattern of ancient humans leaving Africa, becoming isolated, and eventually going extinct, but leaving a distinct fossil record.

They abandoned this "homeland" when natural variations in the Earth's orbit caused it to "wobble" and affect the climate, drying up the wetland into what is now part of the Kalahari desert. But the blood of the people who still live there tells an ancient story.

Prof Hayes says that to understand the genetic differences that lead to disease geneticists first need to know the differences that make humans healthy and able to survive for 190,000 years as hunter-gatherers.

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