Why Europeans have less Neanderthal DNA than Asians

Why Europeans have less Neanderthal DNA than Asians

Skull of a Neanderthal.© Halamka/ iStock

Although Neanderthals were primarily found in Europe, more of their DNA has been preserved in the genomes of today’s East Asians than in Europeans. A study now provides a possible explanation for this phenomenon based on analyzes of ancient DNA. Accordingly, migration movements of our ancestors could have played a decisive role. While early European hunter-gatherers had a comparatively high proportion of Neanderthal DNA, this was diluted when the first Neolithic farmers came to Central Europe from Anatolia.

Around 40,000 years ago, Homo sapiens spread from Africa across the Eurasian continent. For several millennia, our ancestors lived there together with the Neanderthals and sometimes also reproduced with them. Traces of Neanderthal DNA can still be found in our genome to this day. In people in Europe and Asia, Neanderthal DNA makes up around two percent of the genome, although this proportion varies depending on the region. For today’s people from East Asia it is slightly higher than for Europeans. This puzzled science for a long time. After all, the Neanderthals were mainly widespread in the western part of Eurasia. Did their genes perhaps offer more selection advantages in East Asia and therefore remained to a greater extent there?

Migration movements as an explanation

A team led by Claudio Quilodrán from the University of Geneva in Switzerland has now found another plausible explanation. The differences can therefore be explained by the migration movements of our ancestors. For their study, the researchers analyzed the Neanderthal proportion in human DNA from fossil and modern samples from the past 40,000 years. 2,625 published human genomes from across Eurasia were included in the analysis. Using statistical methods, Quilodrán and his team examined how the content of Neanderthal DNA varied depending on time and location. They related this to known migration movements of our ancestors over the last tens of thousands of years.

“Our results show that early migration movements indeed had an evolutionary influence on the location-dependent distribution of Neanderthal DNA,” reports the team. After the first spread of Homo sapiens across Eurasia, the distribution of the Neanderthal genome corresponded to the researchers’ expectations. The further north, i.e. the further away from the area of ​​origin of Homo sapiens in Africa, the higher the proportion of Neanderthal DNA in the population of our ancestors at that time. In addition, according to the analyses, the proportion of Neanderthal genetic material was initially higher in Western Eurasia than in Eastern Eurasia.

“Dilution” by Neolithic farmers

But why did this distribution change? According to Quilodrán and his team, this was not due to selection advantages, but rather to renewed migration movements. Around 10,000 years ago, the first Neolithic farmers from the Fertile Crescent came to Central Europe. Their genome contained significantly less Neanderthal DNA than that of the hunter-gatherers who had previously lived in the region. As a result, the proportion of Neanderthal DNA gradually diluted until it was lower than in East Asia. “This second range expansion is crucial for explaining the currently observed pattern that people in Western Europe have a lower proportion of Neanderthal DNA than people in East Asia,” the researchers write.

These results not only provide an explanation for the current distribution of Neanderthal DNA in various human populations – they also underline how much the migration movements of our ancestors continue to shape the composition of our genome today. “This study shows that the analysis of ancient genomes combined with archaeological data makes it possible to trace different phases in the history of hybridized species,” explain Quilodrán and his colleagues. In addition, it is now possible to describe the percentage of Neanderthal DNA in the genome of Homo sapiens at different times in our prehistory. This could also serve as a basis for future studies.

Source: Claudio Quilodrán (University of Geneva, Switzerland) et al., Science Advances, doi: 10.1126/sciadv.adg9817

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