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.
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.
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.
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.
- 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. Nature, 555(7698), p.652.
- 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. Nature, 512(7514), p.306.
- 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. Nature, 524(7564), pp.216-219.
- 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. Nature, 514(7523), p.445.