Neanderthal extinction caused by tolerance of humans

The Neanderthal extinction has often been explained by innate differences between our species. However, new research suggests our success may have been due to circumstance rather than birth.


Neanderthals dominated Europe for hundreds of thousands of years. Then humans arrived, and Neanderthal extinction followed shortly after. What advantage did we have over them?

New research suggests the answer might be “nothing”.

Rather, Neanderthal extinction was the inevitable result of them not stopping us. They didn’t directly compete with us in Europe1,2, and they didn’t migrate into our African home territory to cut off human “reinforcements”1. This meant we were free to expand unchecked.

Eventually, we simply swamped them with numbers.

Homefield advantage

In sports, we often talk about the home-field advantage. But when it comes to Neanderthal extinction, the fact it was taking place on their home-field of Europe may have been part of their downfall.

Humans evolved in Africa, but soon that town wasn’t big enough for all of us. Around the time Neanderthals went extinct, we were in the middle of expanding around the world. Including into Europe. This meant that, globally, there were probably far more humans than Neanderthals1.

It’s worth noting humans weren’t marching along these arrows like armies conquering the earth. This was a gradual population expansion, driven by offspring searching for a new home in the next valley over.

However, humans didn’t assemble like the Avengers. It’s not like we all came together from around the world to help swamp the Neanderthals. Genetics show the migration into Europe was just one “wave” (hence it being just one red line on the map above)4.

Crucially though, it was a wave of people that would settle and expand. Eventually, a group would grow to big and some would split off and seek a new home. This is how the wave moved forwards. However, the people behind this leading edge of the wave wouldn’t disappear. They would continue to expand, and some would split off again1.

This means that there was a constant trickle of humanity that would gradually overwhelm the Neanderthals. Not in some grandiose way, but with statistics.

When Neanderthals left a territory (perhaps as they track prey) it will probably be occupied by other Neanderthals. However, there’s a small chance some humans may take it over. Since our trickle kept coming, we kept getting new chances, until we were successful. This way, bit by bit, we gradually take over all their territory1.

Tolerant Neanderthals

However, simply introducing a lot of humans into Europe (albeit as a slow trickle) isn’t enough to overwhelm the Neanderthals. They also need to be at least somewhat tolerant of us.

If there was intense competition between our species, our trickle of humans would simply be overwhelmed. Imagine we both needed to hunt mammoths to survive. With a finite number of mammoths in Europe, the numerically superior Neanderthals would have an advantage. They’d kill off all the mammoths leaving us with nothing. Our trickle would cease2.

Instead, we need to be able to get along. If we can coexist, we keep getting those chances to take over some Neanderthal territory. Then the statistics game kicks in and we win1.

Were the Neanderthals tolerant? Our genes imply they might have been since we interbred with each other often. And it wasn’t a one-way thing, human genes also wound up in Neanderthals. But we don’t really know much about the context of these interactions. Just because two people made a baby doesn’t mean they got along.

In fact, there’s some archaeological evidence we didn’t. Neanderthals from Shanidar cave appear to have been killed by human weapons5.

Shanidar 3 discovery

Shanidar 3, whose chest was punctured with a possible human weapon, as he looked when first discovered

Of course, that’s one cave. Can we really infer what all human/Neanderthal interactions were like based on it? However, the reverse is also true. Can we infer how well we got on from a few cases of interbreeding?

Neanderthal extinction postponed

In short, we don’t know if these explanations for human dominance are valid. The statistical models behind them are sound, but they’re still just models. They cut corners and make oversimplify things. The actual archaeological evidence is more ambiguous.

That said, they are a good step forward. Researchers have proposed several possible advantages our species might have had. Things like intellecttechnology, and biological efficiency. However, the evidence that we were significantly better in any of those categories is circumstantial at best3.

These statistical models are more “neutral”. They assume, as the evidence seems to indicate, that our species were more equivalent. How then could we have beaten them? Whether or not reinforcements from Africa and tolerant Neanderthals are the real way, we don’t know. Part of me kind of hopes it is for the poetry of it.

After all, the same “tolerance” in that caused the  Neanderthal extinction also allowed our species to mate. And now their genes live on in most of us.

The same thing which caused their extinction also preserved their legacy.

References

  1. Kolodny, O. and Feldman, M.W., 2017. A parsimonious neutral model suggests Neanderthal replacement was determined by migration and random species drift. Nature communications8(1), p.1040.
  2. Wakano, J.Y., Gilpin, W., Kadowaki, S., Feldman, M.W. and Aoki, K., 2017. Ecocultural range-expansion scenarios for the replacement or assimilation of Neanderthals by modern humans. Theoretical population biology.
  3. Roebroeks, W. and Soressi, M., 2016. Neandertals revised. Proceedings of the National Academy of Sciences113(23), pp.6372-6379.
  4. Posth, C., Renaud, G., Mittnik, A., Drucker, D.G., Rougier, H., Cupillard, C., Valentin, F., Thevenet, C., Furtwängler, A., Wißing, C. and Francken, M., 2016. Pleistocene mitochondrial genomes suggest a single major dispersal of non-Africans and a late glacial population turnover in Europe. Current Biology, 26(6), pp.827-833.
  5. Churchill, S.E., Franciscus, R.G., McKean-Peraza, H.A., Daniel, J.A. and Warren, B.R., 2009. Shanidar 3 Neandertal rib puncture wound and paleolithic weaponry. Journal of human evolution57(2), pp.163-178.

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Neanderthal extinction caused by tolerance of humans

by Adam Benton
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