A groundbreaking study from the University of Pennsylvania reveals that prehistoric humans and Neanderthals interbred with a notable sexual bias, with male Neanderthals mating more often with female modern humans. This pattern may explain the scarcity of Neanderthal DNA in the human X chromosome and highlight the impact of social behaviors on our genetic lineage.
Prehistoric mating preferences help explain why modern humans carry small amounts of Neanderthal DNA in their genomes, particularly absent from the X chromosome. Image credit: Gemini AI.
“In addition to the X chromosome, there’s a significant gap in Neanderthal DNA referred to as the ‘Neanderthal desert’,” stated lead author Dr. Alexander Pratt, a researcher at the University of Pennsylvania.
“Historically, we believed these gaps resulted from certain Neanderthal genes being biologically harmful to humans, leading to their removal through natural selection,” he added.
New genomic analyses indicate that long-standing mating preferences, not genetic incompatibilities, influenced which Neanderthal DNA sequences were retained in modern human genomes.
This research illustrates how social interactions have shaped the human genome and challenges the notion that evolution is solely driven by the “survival of the fittest.”
“Our findings indicate a distinct sexual bias, with gene flow predominantly occurring from male Neanderthals to anatomically modern human females, which explains the limited presence of Neanderthal DNA on modern human X chromosomes,” remarked Dr. Platt.
“Approximately 600,000 years ago, anatomically modern humans and Neanderthals diverged, creating two separate evolutionary paths,” added Professor Sarah Tishkoff, the study’s senior author.
“While our ancestors evolved in Africa, Neanderthals adapted to life in Eurasia, yet this separation was not permanent.”
“Over millennia, human groups migrated into and out of Neanderthal territories, resulting in genetic exchanges during their encounters.”
To assess whether Neanderthal X chromosomes contained modern human alleles, researchers analyzed conserved DNA in three Neanderthal samples: Altai, Chagyrskaya, and Vindija.
They compared this data with that of a diverse genome from Africa, which hadn’t historically interacted with Neanderthals.
“Our analysis revealed a significant discrepancy,” noted co-author Dr. Daniel Harris from the University of Pennsylvania.
“While modern humans lack the Neanderthal X chromosome, the Neanderthal X chromosome contained 62% more modern human DNA compared to other chromosomes.”
This mirrored result indicates that if reproductive incompatibility existed, modern human DNA would also be absent in Neanderthal X chromosomes.
However, the presence of modern human DNA in Neanderthal X chromosomes rules out biological incompatibility as a barrier to reproduction.
The lingering explanation lies in the sexual bias in mating practices.
Given that women possess two X chromosomes and men only one, the direction of mating plays a crucial role.
If Neanderthal males mated more frequently with modern human females, fewer Neanderthal X chromosomes would integrate into the human gene pool, while more human X chromosomes would enter the Neanderthal population.
Mathematical models verified that this bias adequately explains the observed inheritance patterns.
While other factors such as gender-biased migration could lead to similar results, these scenarios are often complex and vary over time and geography.
“Our findings suggest that mating preferences offer the simplest explanation for these patterns,” concluded Dr. Platt.
For more details on this research, refer to the journal Science.
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Alexander Pratt et al. 2026. Interbreeding between Neanderthals and modern humans showed significant sexual bias. Science 391 (6788): 922-925; doi: 10.1126/science.aea6774
Source: www.sci.news
