Ancient DNA Sheds New Light on Human Evolution during Out-of-Africa Migration

May 24, 2023 by News Staff

The dispersal of anatomically modern Homo sapiens out of Africa and across Eurasia provides a unique opportunity to examine the impacts of genetic selection as our species adapted to multiple new environments. An analysis of ancient (1,000 to 45,000 years old) Eurasian genomic datasets reveals signatures of strong selection, including at least 57 hard sweeps after the initial human movement out of Africa, which have been obscured in modern populations by extensive admixture during the Holocene. In new research, scientists identified a previously unsuspected extended period of genetic adaptation lasting around 30,000 years, potentially in the Arabian Peninsula area, prior to a major Neanderthal genetic introgression and subsequent rapid dispersal across Eurasia as far as Australia.

Evolutionary changes that helped our early ancestors survive the first migration out of Africa could hold important clues for modern medicine. Image credit: sjs.org / CC BY-SA 3.0.

“Ancient human genomes make it possible to recover key events in the evolution of our species that are essentially hidden from modern human genomes,” said Dr. Raymond Tobler, a researcher at the Australian National University.

“We suspect the ’Arabian Standstill’ period was a pivotal point in our evolutionary history, during which the ancestors of all non-African humans underwent extensive genetic adaptation to colder environments, effectively preparing them for the cool Eurasian environments they would eventually encounter.”

In their research, Dr. Tobler and his colleagues used ancient human genomes to reconstruct historical adaptation during the poorly understood out-of-Africa diaspora.

They found specific genetic patterns that pointed to a series of natural selection events dating back 80,000 years.

These patterns suggest the ancestors of modern humans living outside of Africa experienced an extended period of genetic isolation and adaptation, possibly around the Arabian Peninsula, prior to their worldwide dispersal 50,000 years ago.

“These ancient adaptive genes share striking functional similarities with selected genes found in human and mammalian populations currently living in the Arctic,” said Garvan Institute’s Professor Shane Grey.

The authors propose a connection between genetic selection and human migration during the Eurasian Paleolithic period, suggesting that the speed of movement was influenced not only by climatic cycles but also by the need to adapt to new environments.

“While crucial for survival at the time, these adaptive genes are associated with obesity, diabetes, and neurodegenerative disease in contemporary populations,” said Dr. Yassine Souilmi, a researcher at the University of Adelaide and the Australian National University.

“Our study not only improves our understanding of human evolution, but the link between adaptation and modern disease could expedite the development of therapeutic and preventive measures by prioritizing medical research on previously selected genes.”

The study appears online in the Proceedings of the National Academy of Sciences.

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Raymond Tobler et al. 2023. The role of genetic selection and climatic factors in the dispersal of anatomically modern humans out of Africa. PNAS 120 (22): e2213061120; doi: 10.1073/pnas.2213061120