After sequencing the Neanderthal genome, the scientists discovered that all current non-African individuals have a Neanderthal ancestry in their DNA. Now, a team of researchers from Princeton University (USA) has presented evidence of Neanderthal ancestry in African populations as well. We continue to unravel the ins and outs of human history.
Humans who migrated from Africa about 60,000 to 80,000 years ago interbred with Neanderthals. That set the stage for some groups to return to Africa carrying Neanderthal genes that spread throughout the continent, according to experts in the study published in the journal Cell.
The sets of Neanderthal genetic variants inherited by modern Africans include genes related to boosting the immune system and modifying sensitivity to ultraviolet radiation. Those genes appear to spread rapidly once they are introduced into African humans.
“Our study is significant because it provides important new insights into human history and Neanderthal ancestry patterns in globally diverse populations,” says study lead author Joshua Akey of Princeton University. “Our results refine the catalogs of genomic regions where the Neanderthal sequence was detrimental and advantageous and demonstrate that remnants of Neanderthal genomes survive in every modern human population studied to date.”
How was it discovered?
The new findings suggest that these estimates could have been biased due to methodological limitations. Thanks to a new statistical approach to detect ancient genetic material still present in modern DNA, it has led to the discovery of a genetic inheritance that has gone unnoticed until now . The new technique also revealed a journey out of Africa roughly 100,000-150,000 years ago that led to the introduction of human genes into Neanderthals through interbreeding.
The researchers applied the new approach to 2,504 modern individuals from the 1000 Genomes Project, representing geographically diverse populations, and used the Altai Neanderthal reference to identify the Neanderthal sequence in these individuals. They distinguished, on average, 17 megabases (Mb) of Neanderthal sequence per individual in the African samples analyzed (corresponding to about 0.3% of the genome), compared to less than one megabase based on the results of previous studies. More than 94% of the Neanderthal sequence identified in African samples was shared with non-Africans.
In conclusion, Africans today possess more Neanderthal ancestry than previously thought.
Study limitations
The authors point to several limitations of their approach. Because IBDmix (the new approach employed) requires an archaic reference genome, it is not ideal for discovering sequences shared between modern humans and unknown or unsequenced lineages. In future studies, the experts plan to apply their approach to additional African populations and study the implications of these archaic sequences for modern human health and disease.
Referencia: Cell, Chen et al.: “Identifying and Interpreting Apparent Neanderthal Ancestry in African Individuals” https://www.cell.com/cell/fulltext/S0092-8674(20)30059-3 , DOI: 10.1016/j.cell.2020.01.012
