Some Neanderthals avoided mating with humans

Neanderthals DNA has been recovered from individuals who lived after humans arrived in the region. Despite this, they lack signs of human DNA suggesting these Neanderthals avoided mating with us.


Humans and Neanderthals coexisted for several thousands of years2. During this time we were more than friends, with interbreeding sharing their genes with us and vice versa.

However, it turns out some Neanderthals may have avoided us.

The genomes of five “new” Neanderthals have been sequenced, revealing a surprising lack of human DNA. It seems that they didn’t want to get in on the interbreeding action1.

It also looks like these Neanderthals avoided their own kind as well. They’re part of a different lineage to Neanderthals living close-by, also suggesting limited interactions between them1.

I guess some Neanderthals were just antisocial.

Finding new Neanderthals

The researchers behind these discoveries didn’t set out to investigate who Neanderthals liked. Instead, they were tackling a different problem. It turns out we don’t have much Neanderthal DNA from after humans arrived in Europe1.

So they screened several Neanderthal fossils from this period, eventually finding five that still had a good chunk of DNA left. These come from across Europe, with some being found at sites where older Neanderthals had already been sequenced1.

Where the new Neanderthal DNA came from. Black dots represent where existing Neanderthal DNA is found.

As such, we can make Dr Who proud and study these Neanderthals in time and space. With this data, we can compare these new Neanderthals to their distant relatives to see how things may have changed.

Plus, we have ancient human DNA from around this time too, providing a further point of comparison. All of them show signs of recent interbreeding with Neanderthals3.

So shouldn’t these Neanderthals show the same thing going the other way?

Neanderthals avoided humans

As I already gave away in the opening, the answer was no. These researchers didn’t find any evidence of interbreeding introducing human DNA into their lineage1. This is notable because the humans living around these time had Neanderthal genes in their recent past3.

Our new family tree, showing all the instance humans (right) interbred with Neanderthals (left)

Gene flow from Neanderthals to humans, but not the other way round. The new Neanderthals confirm this.

In other words, during this period it looks like interbreeding may have been a one-way thing. Genes were flowing into humans, but not the other way round.

However, there are alternative explanations. The scientists behind the analysis of the new Neanderthals offer some words of caution. Although this data does dramatically increase the number of recent Neanderthal genomes we have access too, you could still count them all on your hands. We have a very small sample of the Neanderthal population and we may have just missed the cases of interbreeding1.

This is made all the more plausible by the fact Neanderthals avoided each other. Groups seemed to have lived in relative isolation, so even if their neighbours mated with humans it may not have spread to other populations.

Another possibility is natural selection. We know that Neanderthal DNA is harmful to humans. As such, much of it was quickly purged from our genome by evolution. In fact, some of the contemporary humans already had less Neanderthal than expected, given how close they were to the interbreeding event4.

It might just be the case that natural selection was in overdrive, and purged human DNA from Neanderthals.

Or maybe, the Neanderthals with human DNA went extinct. The other discovery from these new Neanderthal genomes suggests this may have been what happened.

Neanderthals avoided Neanderthals

For most of the new Neanderthals, their lineage matched their location. The recent French Neanderthals were most similar to older French Neanderthals. The recent Belgian Neanderthals were most similar to older Belgians, and so forth.

The Neanderthal family tree, with the new Neanderthals in red. Whilst most Neanderthal sites cluster together, the Russians (circled) fall far apart

There was one exception to this. The Neanderthals from Russia (specifically Mezmaiskaya, in the Caucuses) didn’t fall on the lineage of older Russian Neanderthals. Instead, they seemed more similar to Neanderthals from Western Europe.

This is powerful evidence that the more recent Russian Neanderthals are actually from a different part of Europe. They migrated east, occupying territory once held by the older Neanderthals.

Naturally, this raises questions about what happened to the original Russian Neanderthals. Could it be that they interbred with humans recently, and our harmful DNA drove them extinct?

It can’t be ruled out, but it’s not the most plausible explanation. It also wouldn’t explain why human DNA is missing from the other Neanderthals studied.

Instead, we have to remember we’re dealing with tens of thousands of years between these groups. So many things could have happened that drove the older Russian Neanderthals out of the region. Maybe climate change wiped them out. Maybe they were driven out by humans. Or maybe, they left of their own devices, living a naturally mobile hunter-gatherer lifestyle.

One thing is clear though. Ancient Europe was complicated. Populations were coming and going. Mating was happening but only in weird ways.

This story probably has many more twists left to come.

References

  1. Hajdinjak, M., Fu, Q., Hübner, A., Petr, M., Mafessoni, F., Grote, S., Skoglund, P., Narasimham, V., Rougier, H., Crevecoeur, I. and Semal, P., 2018. Reconstructing the genetic history of late Neanderthals. Nature555(7698), p.652.
  2. Higham, T., Douka, K., Wood, R., Ramsey, C.B., Brock, F., Basell, L., Camps, M., Arrizabalaga, A., Baena, J., Barroso-Ruíz, C. and Bergman, C., 2014. The timing and spatiotemporal patterning of Neanderthal disappearance. Nature512(7514), p.306.
  3. Fu, Q., Hajdinjak, M., Moldovan, O.T., Constantin, S., Mallick, S., Skoglund, P., Patterson, N., Rohland, N., Lazaridis, I., Nickel, B. and Viola, B., 2015. An early modern human from Romania with a recent Neanderthal ancestor. Nature524(7564), pp.216-219.
  4. Fu, Q., Li, H., Moorjani, P., Jay, F., Slepchenko, S.M., Bondarev, A.A., Johnson, P.L., Aximu-Petri, A., Prüfer, K., de Filippo, C. and Meyer, M., 2014. Genome sequence of a 45,000-year-old modern human from western Siberia. Nature514(7523), p.445.

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4 thoughts on “Some Neanderthals avoided mating with humans”

  1. nova9 says:

    Its called killing off your enemy while taking their females as booty.

    Neanderthals were cave monopolist (keeping possession of a cave shelter year round). Such behavior assured them shelter when winter conditions returned. But such behavior always kept their numbers extremely limited.

    Once nomadic non Neanderthal populations (probably from the middle east) learned how to efficiently internally heat tepees, they didn’t have to monopolize caves in order to survive in ice age Europe and could live practically anywhere. So their population in Europe exploded, overwhelming the limited populations of the cave monopolist Neanderthal communities.

    Neanderthals probably had to hunt much further away from their home base since animals would have learned to avoid the area near their permanent cave shelters. And this probably left Neanderthal females much more vulnerable to being captured by nomadic hunters from non Neanderthal communities.

    Marcel

    1. Adam Benton says:

      The foundation of your idea is just untrue. Neanderthals only occupied sites seasonally, as indicated by the fact faunal remains are often dominated by a seasonal animal. Plus, there are many open-air Neanderthal sites. They just tend to be rarer because they’re less likely to be preserved. Caves protect the archaeology, so we wind up with more of them just as a quirk of what survives.

  2. Rodrigo Singer says:

    Perhaps I am being naive and/or pressed. But couldn’t this evidence sugggest that Neantherthal females were raped in some places?

    1. Adam Benton says:

      With the gene flow only entering humans, it would mean any rape was going the other way. Although even that seems unlikely as these Neanderthals were far removed from any interbreeding, one way or the other, based on the genetic distance between them and any interbreeding event.

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Some Neanderthals avoided mating with humans

by Adam Benton
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