“The result of prehistoric sexual contacts between our ancestors and Stone Age hominids”
Some groups of modern humans appear to have more Neanderthal DNA than others. Scientists have long been intrigued by this data, wondering why this is happening. New research offers answers.
New analysis of ancient genomes deepens scientists' understanding of the Neanderthal DNA carried by human populations in Europe and Asia — genetic traces that may have medical significance today, CNN reports.
Researchers say , a discovery published Wednesday in the journal Science Advances, tracks the genetic legacy of our species' archaic relatives, Homo sapiens, with greater precision thanks to a critical mass of invaluable data.
Most people alive today can trace a very small percentage of their DNA back to Neanderthals — the result of prehistoric sexual encounters between our ancestors and now-extinct Stone Age hominids before the latter disappeared about 40,000 years ago.
However, Neanderthal DNA is somewhat more common in the genomes of East Asian populations, CNN notes.
This discrepancy has long puzzled scientists, since Neanderthal remains have been found in large numbers throughout Europe and the Middle East, but no further east than the Altai Mountains in Central Asia.
“So what's puzzling is that «It's that in an area where we've never found Neanderthal remains there appears to be more Neanderthal DNA,» says study co-author Mathias Currath, senior lecturer in genetics and evolution at the University of Geneva.
On average, Kurrat says, Neanderthal DNA makes up about 2% of the genetic makeup of people in Eurasia, while in East Asia the share can be as high as 4%.
Kurrat and his colleagues at the University of Geneva have found an explanation for this discrepancy. , by analyzing the distribution of DNA inherited from Neanderthals in human genomes over the past 40,000 years.
“We are beginning to have enough data to increasingly accurately describe the percentage of DNA of Neanderthal origin in the sapiens genome at certain periods in prehistory ”, Kurrat explained.
The researchers found that over time, the distribution of Neanderthal DNA did not always look as it does now.
The research team extracted information from a database containing more than 4,000 ancient genomes from across Europe and Asia, compiled by a team led by Dr David Reich Professor of Genetics and Human Evolutionary Biology at Harvard Medical School in Boston.
The researchers found that the genomes of Stone Age Homo sapiens, who lived as hunter-gatherers in Europe after the Neanderthal extinction, contained a slightly higher proportion of Neanderthal DNA than those who lived in Asia, for samples more than 20,000 years old.
The research team therefore concluded that the current trend towards a higher percentage of Neanderthal ancestry in Asian populations compared to European populations must have developed at a later stage, most likely during the Neolithic transition period, when agriculture began to replace hunting and gathering as a way of life around 10,000-5,000 years ago.
At this point in time, the first farmers from Anatolia, in what is now western Turkey and the Aegean Sea, began to mingle with the existing hunter-gatherers in Western and Northern Europe. This resulted in a decrease in the proportion of Neanderthal DNA observed in European genomes during this period.
“The point is that they had less Neanderthal ancestry, so they diluted (Neanderthal ancestry) in European populations,” Karratt said.
He said it was less clear how this transition happened in Asia due to a relative lack of information. The study included 1,517 samples from Europe versus 1,108 from Asia—more than four times the area.
Tony Capra, associate professor of epidemiology and biostatistics at the Bacharach Institute for Computational Health Sciences at UCSD Francisco, said the paper is “an example of a very exciting and promising strategy for integrating the analysis of ancient human DNA from different geographic locations with modern genomes to connect the dots of evolution across time and space.” He was not involved in the study.
Some genetic traces left by encounters with Neanderthals may affect the health of modern humans. For example, according to a September 2020 study, Neanderthal DNA may play a small role in changing the course of Covid-19 infection.