A new genetic study has revealed that when modern humans began interbreeding with Neanderthals around 50,000 years ago, most of the pairings were between human women and Neanderthal men.
According to a team led by Professor Alexander Platt, this tendency for Neanderthal men and human women to pair may explain the presence of so-called “Neanderthal deserts” in human chromosomes. These are regions in the modern human genome where Neanderthal genes are rarely found.
As a result, researchers now have a better idea why contemporary humans carry relatively little Neanderthal DNA. The team noted that most people of non-African descent today carry, on average, about 2 percent Neanderthal ancestry.
What did the research reveal?
Since the first genomes of modern humans and Neanderthals were sequenced more than 20 years ago, scientists have been puzzled by the phenomenon of “Neanderthal deserts.”
Experts were baffled that genes inherited from Neanderthals could be found only in tiny segments of the human X chromosome, even though those genes are more prevalent on other chromosomes. Moreover, the X chromosome of modern humans contains areas completely devoid of Neanderthal genes.
“For many years, we assumed that these ‘Neanderthal deserts’ existed because certain Neanderthal genes were biologically toxic to humans (as is often the case during species divergence), so we thought these genes might cause health issues and were likely eliminated by natural selection,” Professor Platt explained.
However, during their research, the team concluded that the most plausible explanation for the “Neanderthal deserts” is partner preference—an evolutionary mechanism that plays a crucial role in sexual selection.
The scientists analyzed the genomes of 73 women from three modern African populations without Neanderthal ancestry and compared them to the genomes of several Neanderthals.
The researchers examined Neanderthal X chromosomes and found far more modern human gene fragments on those X chromosomes than on Neanderthals’ other chromosomes. This finding indicated that the absence of Neanderthal genes on the human X chromosome is not due to incompatibility, as reported by Live Science.
Rather, the surprisingly large number of modern human DNA fragments found in Neanderthals can be attributed to partner selection preferences, the researchers believe. Because human females have two X chromosomes while males have only one, pairings between human women and Neanderthal men would have introduced fewer Neanderthal X chromosomes into the human gene pool.
However, the reasons behind the mutual attraction between human women and Neanderthal men remain unclear.
As Professor Platt stated, his team plans to “explore the evolution of social structures and gender roles among Neanderthals” in hopes of ultimately unraveling this mystery.
The results of the study were published in the journal Science.
