Neanderthal and human interbreeding followed a specific pattern
A new study shows that interbreeding between Neanderthals and ancient anatomically modern humans occurred primarily between male Neanderthals and female humans.
A Neanderthal man in the Human Evolution exhibition at the Natural History Museum, London.
Mike Kemp/In Pictures via Getty Images
Most people today have a little Neanderthal DNA scattered throughout their genome. These genomic signals indicate that overlapping populations of ancient anatomically modern humans and Neanderthals had interbreeding. What these negotiations actually looked like is a mystery, but a new study Turns out that when our species and Neanderthals interbred, it was primarily between male Neanderthals and anatomically modern female humans.
There is less Neanderthal DNA on the X chromosome of humans today than on most other chromosomes. There were other theories about why this might have happened, including the possibility that there was some evolutionary loss in the Neandertal X chromosome in humans.
“Our study allowed us to distinguish between these possibilities,” says study co-author Sarah Tishkoff, a professor of genetics and biology at the University of Pennsylvania.
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Researchers compared ancient Neanderthal DNA with DNA from people living in Africa today who have little or no Neanderthal ancestry.
If the mixing of physiologically modern human and Neanderthal DNA was harmful, scientists theorized, Neanderthal genomes would show large gaps devoid of human DNA, similar to the lack of Neanderthal DNA on today’s X chromosomes. H. Sapiens, explains Alexander Platt, a senior research scientist at the University of Pennsylvania and lead author of the study. “But what we found was that was not the case,” he says.
Instead there was much more physically modern human ancestry present on the Neanderthal X chromosome than researchers expected, including in regions that had nothing to do with fitness. This suggested that the apparent absence of Neanderthal DNA in parts of the genome of humans today is probably the result of a strong gender bias in very early mating.
This research was published in the journal on Thursday Science.
Tishkoff explains that scientists already knew that this could happen. But it is unclear why male Neanderthals could selectively mate with physiologically modern female humans, or vice versa. “One can only guess!” Tishkoff says.
A major limitation of the study is that the team didn’t have a ton of Neanderthal DNA to work with — there are only a handful of high-quality Neanderthal genomes. And these genomes provide just a snapshot of what sex might have looked like between Neanderthals and anatomically modern humans at one time.
As anthropologists work to uncover more Neanderthal DNA in the fossil record, the anatomically modern human-Neanderthal genetic picture will become clearer, Platt says.
Platt says that in a more philosophical sense, the study shows the importance of looking outside of human DNA to understand our own ancestry.
“We don’t have to just look at our own gene pool to know what happened to Neanderthal alleles when they came into our population,” he says. By looking at the other part of these interactions in Neandertals, “you get a much richer picture.”
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