A new genetic study has suggested that male Neanderthals interbred with human females in sexual relationships dating back tens of thousands of years.

The study, which was published on Thursday in the journal Science, suggested that Neanderthal DNA was found in the genomes of present-day humans, indicating gene flow from male Neanderthal populations into the female ancestors of modern humans.

According to the study, male Neanderthals and members of the human species exchanged DNA multiple times through sexual intercourse over the past 250,000 years due to the migration of both species from one region to another.

It indicated that most humans might carry a small percentage of Neanderthal DNA as a genetic legacy from those sexual interactions.

The study further noted that the lingering genetic legacy from those sexual interactions can, in certain cases, still influence human health, as Neanderthal DNA can affect circadian rhythms, immune system function, and the way some people feel pain, CNN reported.

According to the lead researcher at the University of Pennsylvania, Alexander Platt, analysis also revealed an excess of modern human DNA on the Neanderthal X chromosome. At the same time, it was discovered that there was limited evidence that Neanderthal X chromosome DNA entered the modern human gene pool in significant amounts.

Mr Platt said, “It’s a story that involves who has X chromosomes. We did not get as many X chromosomes from those Neanderthal males, and they got an excess of modern human ancestry on their X chromosomes.”

He proposed that “mate preference” could offer a possible explanation for the pattern, suggesting that male Neanderthals, female modern humans, and Neanderthal females with more human ancestry may have been perceived as more desirable partners.

Mr Platt also noted that female Homo sapiens who encountered Neanderthal males may have viewed them as more alluring sexual partners.

The study further suggested that after episodes of interbreeding, subsequent generations of Neanderthal males were more likely to mate with Neanderthal females who already carried greater levels of modern human ancestry.

Neanderthals, who lived across Europe and parts of western Asia, became extinct around 40,000 years ago.

The study suggested that in modern times, most people of non-African descent carry about 1–2% Neanderthal DNA, a lasting legacy of those early sexual encounters.

According to the researchers, the study provides more insight into how interbreeding shaped the evolutionary history of both species, highlighting the complex nature of human origins.