Modern humans arrived in Europe around 45,000 years ago. There, we met the Neanderthals who had been living on the continent for nearly 1 million years. Despite this long history, we “won” this encounter and the Neanderthals went extinct within a few tens of thousands of years. A rapid end for an ancient species.
Some have suggested the extinction of Neanderthals was actually a long time coming. It turns out their population may have been on the decline before we even showed up. Perhaps they were already vulnerable to extinction and we just tipped them over the edge.
Or at least, that’s what preliminary reports suggested. A recent, thorough review has revealed the opposite might be true. Neanderthals were actually flourishing as humans arrived.
Neanderthals on the decline
The first indicators Neanderthals were in trouble as humans arrived come from the distant past of 2014 when a Neanderthal toe was found in the Altai Mountains. Specifically, in Denisova Cave; notable for containing another mysterious species.
Now, a Neanderthal toe on its own isn’t that interesting. Even one from a cave where another hominin lived. However, they managed to extract some DNA from it, revealing the owner was a woman. It also revealed that she was a little bit too Lannister-y. Their parents were at least half-siblings, and similar levels of interbreeding seem to have been common in her recent past.
This level of interbreeding implies Neanderthal populations may have been small. This fact seemed to be backed up by the lack of diversity in the genome. They had ~20% the number of heterozygous genes of modern Africans. Based on this, the discoverers of this Neanderthal Cersei estimated that the Neanderthal population was on the decline, trending towards extinction.
Additionally, Neanderthals had a higher number of deleterious mutations. This indicates there was a lot of genetic drift in the population, a tell-tale sign of a small population. It may also explain why so many of the genes we inherited from them through interbreeding were harmful.
So Europe was occupied by a small, inbred population of Neanderthals when humans arrived. Is it any surprise that we survived whilst they went extinct?
Neanderthals were actually doing well
So that’s all the evidence things weren’t going great for Neanderthals. What changed? Well, nothing really. It’s still fairly clear that the Altai Neanderthal was the result of inbreeding and part of a declining population.
However, new evidence indicates these were problems unique to the Altai group, rather than Neanderthals as a whole. Those living in the Siberian Mountains were in the decline and inbreeding. Neanderthals elsewhere were actually flourishing.
The evidence for how additional populations were doing comes from, well, additional population. Data from the Altai Neanderthals was compared with Denisovans and hundreds of humans. This, combined with improvements to the methodology, failed to find the evidence of the widespread population decline looking at Altai alone found. Instead, there were likely tens of thousands of Neanderthals across Europe. Hardly the dwindling group that could easily pushed over by arriving humans.
Early troubles for Neanderthals
That chart above has a very interesting point you may have missed. The population size estimates for the last common ancestor of Neanderthals and Denisovans is very small. This isn’t a mistake. Shortly after the Neanderthal/Denisovan branch split from the modern human branch, their population plummeted.
It is worth noting that the population estimate for before this split was also quite small. As such, this isn’t quite as dramatic as it looks. But it still indicates a fairly substantial population decrease in early Neanderthals/Denisovans.
The exact significance of this is unknown. The split happened close to 750,000 years ago. We don’t have an awful lot of fossils from this period, and no DNA. For all we know there might be something super interesting happening. But what is clear is that Neanderthal populations eventually recovered.
Humans arrived to find a continent occupied by a whole other species. But that didn’t stop us.
Prüfer, K., 44. authors (2014). The Complete Genome Sequence of a Neanderthal from the Altai Mountains. Nature, 505(7481), pp.43-49.
Rogers, A.R., Bohlender, R.J. and Huff, C.D., 2017. Early history of Neanderthals and Denisovans. Proceedings of the National Academy of Sciences, p.201706426.