Ancient Interbreeding Reveals Preference for Neanderthal-Human Pairings
New genetic research published in Science suggests that when Neanderthals and early modern humans interbred, pairings were more likely to occur between male Neanderthals and female Homo sapiens. The study offers a potential explanation for the observed scarcity of Neanderthal DNA on the human X chromosome, a region typically inherited from one’s mother.
Uncovering Ancient Mating Patterns
Researchers led by Alexander Platt at the University of Pennsylvania and Sarah Tishkoff analyzed DNA from Neanderthal remains – including specimens from Altai, Chagyrskaya, and Vindija – and compared it to genetic data from sub-Saharan African populations, which have limited Neanderthal ancestry [1]. They discovered a significant excess of modern human DNA on the Neanderthal X chromosome, with a 62% increase, confirming the limited presence of Neanderthal DNA in this region of the human genome [1].
The findings suggest that the observed pattern isn’t necessarily due to genetic incompatibility between the two species, but rather reflects long-term mating preferences [2]. Because females carry two X chromosomes while males have only one, the direction of mating significantly impacts gene flow. If male Neanderthals more frequently partnered with human females, fewer Neanderthal X chromosomes would have been passed down through generations [4].
The ‘Neanderthal Desert’ Explained
Modern humans can carry up to 4% Neanderthal DNA, but this genetic material isn’t evenly distributed across the genome. Certain regions, particularly on the X chromosome, exhibit a marked absence of Neanderthal ancestry, often referred to as “Neanderthal deserts” [3]. Previous theories proposed that Neanderthal genetic variants were disadvantageous and therefore purged from the population, but this new research points to behavioral factors as a primary driver [3].
“These are all people, and we know that people have bias, and we know people have preferences,” explained study co-author Alexander Platt, an evolutionary geneticist at the University of Pennsylvania [2]. He noted that geneticists have often taken a “bizarrely clinical approach” to studying ancient genomes, overlooking the role of individual preferences and social dynamics.
Remaining Questions
The exact reasons behind this mating preference remain unclear. Researchers speculate whether human women ventured into Neanderthal territories, or if Neanderthal males were drawn to larger human groups [4]. The nature of these interactions – whether peaceful, accidental, or even coercive – is similarly unknown.
“I don’t know if we’ll ever get a definitive answer to how this happened, since we can’t travel back in time,” said population genetics expert Xinjun Zhang with the University of Michigan, commenting on the new analysis [4].