Why do some groups of people today have more Neanderthal DNA than others? A new study offers answers.
Neanderthal skull : Most people today have relatively little Neanderthal DNA.
Neanderthal DNA has been found in modern humans from Europe and Asia, and this discovery, along with others made possible by the sequencing of ancient genomes, may one day have practical medicinal applications.
This discovery, which was published on Wednesday in the journal Science Advances, allows for more precise tracking of the genetic heritage of our ancient Homo sapiens ancestors, the researchers said.
A tiny fraction of modern humans’ ancestry comes from Neanderthals, a consequence of sexual interactions between our ancestors and the extinct Stone Age hominins before their extinction some 40,000 years ago.
However, East Asian populations’ genomes include a slightly higher proportion of Neanderthal DNA than those of other regions.
The absence of Neanderthal fossils east of the Altai Mountains in Central Asia has perplexed researchers ever since the initial finds in Europe and the Middle East.
Mathias Currat, a senior professor in genetics and evolution at the University of Geneva and coauthor of the research, said, “So what’s puzzling is that in an area where we’ve never found any Neanderthal remains, there’s more Neanderthal DNA.”
Currat estimates that Neanderthal DNA makes up approximately 2% of the average person’s genome across Eurasia, but as much as 4% in East Asia.
Currat and his colleagues at the University of Geneva determined the cause of this discrepancy by examining the patterns of Neanderthal DNA incorporation into modern human genomes over the last 40,000 years.
During prehistoric times, “we are beginning to have enough data to describe more and more precisely the percentage of DNA of Neanderthal origin in the genome of Sapiens,” Currat said.
What the researchers discovered is that the pattern of Neanderthal DNA distribution has changed over time.
The Genome’s Dilution
Dr. David Reich, a professor of genetics and human evolutionary biology at Harvard Medical School in Boston, and his colleagues compiled a database of over 4,000 ancient genomes from Europe and Asia, which the study team used to conduct their research.
Stone Age European hunter-gatherers who lived after the demise of the Neanderthals have a somewhat larger amount of Neanderthal DNA in their genomes than their Asian counterparts for samples older than 20,000 years.
Researchers came to the conclusion that the current trend of Asian populations having a higher percentage of Neanderthal ancestry than European populations must have started later. It probably started during the Neolithic period, when farming started to replace hunting and gathering around 10,000 to 5,000 years ago.
Early in European history, hunter-gatherers in Western and Northern Europe started to intermarry with agriculturalists from Anatolia, in what is now western Turkey and the Aegean. The outcome was a decline in the amount of Neanderthal DNA found in European genomes at that time.
Currat said that since these people “had less Neanderthal ancestry, they diluted the Neanderthal ancestry) in European populations.”
He noted that there was little information available on how this change occurred in Asia. There were four times as many samples from Europe (1,517 total) as from Asia (1,108 total).
An expert in the field of epidemiology and biostatistics at the University of California, San Francisco, Tony Capra, called the paper “an example of a very exciting and promising strategy for integrating analysis of ancient human DNA from different geographic locations with modern genomes to connect the dots of evolution through time and space.” Away from the study, he contributed nothing.
Some of the genetic footprints left by interactions with Neanderthals may have a positive effect on present-day human health. The results of research scheduled for publication in September 2020 suggest, for instance, that Neanderthal DNA may have a minor impact on influencing the course of COVID-19 infection.
