Genetics suggests that Neanderthal males preferred human females

We have known for years that today’s non-African populations They preserve between 1 and 4% Neanderthal DNA as a legacy of the prehistoric crossings that existed. However, when looking at our X chromosome (which determines sex), geneticists repeatedly encountered an absolute void, a phenomenon that has been dubbed ‘neanderthal desert‘since there was no ancient DNA. And the question here is quite obvious: Why did the imprint of this species disappear from our sex chromosome, but not from the rest of the chromosomes?

The key data. From here science began to investigate, and a new published article in Science proposes an answer much more focused on demographics: sex between both species It had a very strong gender bias. That is to say, the fact that a member of each species had sexual relations with great frequency has survived to this day with this genetic imprint.

How do you know? What was done to be able to see what happened to the genetic material and its passage between generations within the Neanderthal populations was simply to analyze genomes. Specifically, the DNA of women from current African populations, who do not have any Neanderthal genetics, and compared them with genomes of female Neanderthals, mainly the Neanderthal of Altaibut also specimens of Chagyrskaya and Vindija.

The result. Here the researchers realized that the X chromosome of the Neanderthals analyzed presented a large amount of DNA that came from the Homo sapiens. Specifically, an excess of 62% was seen compared to the rest of the organism’s chromosomes.

The only thing that confirms is that the genetic exchange between both species was not a one-way change, but rather that both parties were enriched, causing the Neanderthals to also have sapiens DNA, but in different proportions.

A matter of preferences. How is such a brutal asymmetry in the sex chromosomes explained? Until now, the most accurate hypothesis to justify our “Neanderthal desert” was biological incompatibility between species. Here it was thought that male hybrids suffered fertility or viability problems if they received this DNA, which caused a negative selection of testicular genes that erased the Neanderthal imprint of our X chromosomes.

However, science has now ruled out that this 62% excess on the Neanderthal side is due to the sapiens DNA giving them an evolutionary advantage, since they ended up disappearing in a until now inexplicable way.

The conclusion. Everything indicates here that there was an extreme sexual bias in the miscegenation. That is, the crossings occurred overwhelmingly between Neanderthal males and females. Homo sapiens, and always with this pattern.

This mating preference persisted across generations, where Neanderthal males preferred females sapiensand the resulting hybrid offspring were also “preferred” in group dynamics. In this way we are faced with the piece that fits into the bidirectional puzzle of our evolutionary history.

There are nuances. As usual, there is always a ‘but’ in these stories. In this case, the researchers point out that, although the genetics are quite clear, the behavioral interpretation has nuances, since the pattern we see today could be the result of a mixture of factors.

One of them is that societies where women sapiens They left their tribe to join the clans of their Neanderthal partners, introducing their X chromosome into the genetic pool of the other species.

Images | Jan Jakubowski

In Xataka | The extinction of Neanderthals has always been a mystery. Science now believes that they are still with us