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Study pinpoints the origin of modern humans

A landmark study pinpoints the birthplace of modern humans in southern Africa and suggests how past climate shifts drove their first migration.

Anatomically modern humans originated in Africa around 200 thousand years ago. Although some of the oldest skeletal remains suggest an eastern African origin, southern Africa is home to contemporary populations that represent the earliest branch of human genetic phylogeny.

In a new study, scientists collected blood samples to establish a comprehensive catalog of modern human’s earliest mitogenomes from the so-called ‘L0’ lineage. The contribution of local communities and study participants in Namibia and South Africa allowed scientists to uncover rare and new L0 sub-branches.

First author Dr. Eva Chan from the Garvan Institute of Medical Research, who led the phylogenetic analyses, said, “We merged 198 new, rare mitogenomes to the current database of modern human’s earliest known population, the L0 lineage. This allowed us to refine the evolutionary tree of our earliest ancestral branches better than ever before.”

Scientists then combined the L0 lineage timeline with the linguistic, cultural, and geographic distributions of different sublineages. They found that 200 thousand years ago, the first Homo sapiens sapiens maternal lineage emerged in a ‘homeland’ south of the Greater Zambezi River Basin region, including (k the entire expanse of northern Botswana into Namibia to the west and Zimbabwe to the east.

The study, in addition, suggests that the ancient wetland ecosystem provided a stable ecological environment for modern humans’ first ancestors to thrive for 70 thousand years.

Study lead Professor Vanessa Hayes from the Garvan Institute of Medical Research, and University of Sydney reported, “We observed significant genetic divergence in the modern humans’ earliest maternal sub-lineages, that indicates our ancestors migrated out of the homeland between 130 and 110 thousand years ago. The first migrants ventured northeast, followed by a second wave of migrants who traveled southwest. A third population remained in the homeland until today.”

“In contrast to the northeasterly migrants, the southwesterly explorers appear to flourish, experiencing steady population growth. The authors speculate that the success of this migration was most likely a result of adaptation to marine foraging, which is further supported by extensive archaeological evidence along the southern tip of Africa.”

What may have driven these early human migrations?

To figure out the answer, scientists analyzed climate computer model simulations and geological data, which capture Southern Africa’s climate history of the past 250 thousand years. They found that the slow wobble of Earth’s axis changes summer solar radiation in the Southern Hemisphere, leading to periodic shifts in rainfall across southern Africa.

Co-corresponding author Professor Axel Timmermann, Director of the IBS Center for Climate Physics at Pusan National University said, “These shifts in climate would have opened green, vegetated corridors, first 130 thousand years ago to the northeast, and then around 110 thousand years ago to the southwest, allowing our earliest ancestors to migrate away from the homeland for the first time.”

Professor Hayes reported, “These first migrants left behind a homeland population. Eventually, adapting to the drying lands, maternal descendants of the homeland population can be found in the greater Kalahari region today.

The study published in the Journal Nature- was conducted in consultation with the local African communities, approval from community leaders, and ethics approval from the Ministry of Health and Social Services in Namibia, the University of Pretoria Human Research Ethics Committee and St Vincent’s Hospital, Sydney.

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