Short read: Neanderthal men mated with Homo sapiens women. It was a matter of preference, study finds

For many years biologists have been puzzled by the fact that “the X chromosome in modern humans has a minimal amount of Neanderthal DNA.

The X chromosome is one of the sex chromosomes. Women have two X chromosomes, while men have an X and a Y chromosome.

“In contrast, autosomes—the non-sex chromosomes numbered 1 through 22—contain on average five times more Neanderthal DNA than the X chromosomes in people today,” writes Science.”

For decades two different types of theories have been entertained in order to explain why the X chromosome has so little Neanderthal DNA. The first theory is that this is an accident. The alternative theory is that this is due to “Imbalanced coupling of men and women with different genomes”.

The 26^th February 2026 issue of Science contains an article titled “Interbreeding between Neanderthals and modern humans was strongly sex biased’.” Effectively, the article validates the alternative theory citied above i.e. the X chromosome has so little Neanderthal DNA because Neanderthal men mated with Homo Sapiens women (whereas the other theoretical pairing – Homo Sapiens men with Neanderthal women – rarely took place.)

This remarkable finding obviously begs lots of questions such as why & when? Let’s first focus on the ‘when’: “They write that it was not a single episode or a short window of contact, but rather a few thousand-year-long pattern of interaction.

“The Neanderthal DNA that persists in people today comes from an episode of interbreeding between 49,000 and 45,000 years ago, only a few thousand years before Neanderthals vanished,” reads an article in Science.”

Now, let’s focus on the ‘why’: “The interactions took place between modern humans who moved from the African subcontinent to Eurasia and the Neanderthals who had lived there for millennia.

While the researchers did not assign a reason to this preference—consensual or violent—Steven Churchill, a Duke University paleoanthropologist, speaking to Science, concludes the process was aggressive.

“It’s hard to reconcile that [males from one species monopolising females from the other] with anything but a competitive, unfriendly interaction.”

In plain English what this means is that when the homo sapiens from Africa moved into Europe and Asia, they encountered the Neanderthals who lived there. These Neanderthals ended up mating with the homo sapiens women after beating up their men in a punch-up. Those who claim Eurasian descent are effectively the descendants of that inter-species mating.

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