Why did neanderthals go extinct?

Emma Pomeroy took this question from Megan...

Emma - Well it's a tricky one. Honestly. It's something that we've been debating for decades and I still don't think we have a clear answer. If we go back sort of a number of decades, it was assumed that Neanderthals were not as intelligent as modern humans. And so it's rather coincidental perhaps that Neanderthals go extinct just about the time that modern humans spread and become successful in Europe. So some people have argued, well, perhaps they just weren't as good as catching animals and they weren't as flexible in the kind of plants they could eat. However, the evidence we're getting now is that that gap in sort of cognitive ability, so mental capacity was not so great as we used to assume. We've got evidence for things like decoration of the body in Neanderthals, symbolic things that signal that higher level of intelligence. Some other ideas have been put forward, and these have been somewhat revolutionized actually by studies of genetics and ancient DNA. We can see that among the Neanderthals, especially those just before they went extinct around 40,000 years ago, that genetic diversity is really low. So we can look at Neanderthals from across their range and there's not much variation between them. And that's really important because we know that once species start to lose their genetic diversity, they become very susceptible both to inherited diseases but also infectious diseases. So it's possible that that loss of diversity could actually have led to their extinction.

Phil - What would that have come from though?

Emma - That's another tricky question.

Phil - You get that from inbreeding, that's the main one, correct?

Emma - Yes, exactly. Inbreeding. And what we think must have been happening was that their population levels were very, or relatively low compared to modern humans. Now, why that is again, is a difficult question to answer. It could be because perhaps the rate of reproduction and the rate of population growth was lower. Perhaps it's been suggested that as the climate fluctuated over sort of the centuries and millennia, their preferred habitats kind of became more common so the population could spread out. But then in the intervening periods they got restricted to really small areas and many died out. So over time that variability got less and less.

Phil - Is it possible that it was less passive aggression from us and more, you know, actual aggression?

Emma - Well that's a possibility. So we're not the nicest. We can be very compassionate and nice, but we can do nasty things to each other as well. And there are arguments that, you know, we were involved in extinction of Neanderthals, maybe intentionally, maybe unintentionally. The evidence for an intention of involvement is pretty thin on the ground. We have one Neanderthal from a site called Chandar cave in Iraqi Kurdistan, from around the time that Neanderthals were going extinct, and he has an injury to one of his ribs that comes from a projectile. So traditionally those are associated with our own species, modern humans, as having that ability to make this more kind of advanced technology. So some people have said perhaps that's one example of modern humans killing off Neanderthals.

Phil - The earliest episode of CSI probably to date!

Emma - Well it could be! Another less intentional way that we might have helped to kill off Neanderthals is actually through the spread of disease. So it's been suggested that modern humans, who (we) evolved in Africa, and then we spread out into Europe where Neanderthals were. And probably what we brought with us was a whole load of new diseases that the Neanderthals had never encountered before. So they didn't have the evolved immunity to actually be able to fight off those diseases. Now, in some cases, you know, new diseases come or introduce and they spread and they can be serious, like with coronavirus at the moment. But the rate of mortality is not necessarily huge, but we know of other examples. For example, when Europeans first went to the Americas and took with them smallpox, that had a devastating effect on the native populations there because they'd never been exposed. They had no immune response that had evolved and the genes that you need to be able to fight that off. So maybe we're seeing a similar scenario with Neanderthals and modern humans, especially if the Neanderthals were already rather inbred and perhaps lacking the genetic diversity that would have given them strong immunity.