The Neanderthals were very similar to us; to the point where we could even interbreed. Even their technology was equivalent to ours ( although that's because they stole it). Despite these similarities only one of us survived to the climate change of the ice age to the present. Clue: it wasn't the Neanderthals.
Given these similarities, why they died out remains one of the biggest mysteries about human evolution. We have some promising ideas, but nothing concrete. However, although the why is still unknown researchers are beginning to hone in on how the extinction happened.
The secret is in fossil teeth. These track changes in diet. Or, in the case of humans, lack of changes. It turns out climate change had relatively little impact on our ancestors' lives. Neanderthal diets, on the other hand, were strongly influenced by the environment.
It seems that we were able to adapt to the environment. Why is still a mystery, but the fact remains this would have given us an advantage over our big-browed cousins.
Taking a bite out of climate change
You could clean your teeth every day and make them look perfect. But that isn't going to undo all the damage your diet does to them. The food you eat causes microscopic scratches and abrasions. A tell-tale fingerprint of what you've been doing.
Albeit, a very low resolution fingerprint. Looking at this sort of microwear can tell us if you've been eating between "hard" and "soft" food. But for more detail we must turn to another method, like stable isotope analysis. That's why microwear generally plays second fiddle in the study of human evolution. Until an international team of researchers realised that microwear could provide a lot of information about something else: dietary change.
Microwear might not be good at telling you exactly what was eaten, but its easy to study and present on every tooth. So it's possible build up a huge database of tooth damage over time. Whilst we might only have 13 Neanderthals with stable isotope data available, these researchers could obtain information on more than 50 Neanderthals' teeth. This information was compared to the local environment (at the time the Neanderthals were alive. It's changed a bit since then). They also repeated this same process with modern humans living around the same time.
This comparison revealed the environment had a major impact on Neanderthal microwear and - by extension - diet. In particular, the variety of damage done to Neanderthal teeth was much reduced in some environments (particularly open ones). This could indicate that Neanderthals diet became a lot narrower in these locales, perhaps because they weren't well suited to hunting in them. Alternatively, it might be that they could focus on their preferred prey in open environments. When they found themselves in woodland the increased variety indicates them being forced to generalise because they can't keep exploiting their preferred prey.
Either way, it's clear environmental change had a big impact on the Neanderthal diet. Yet the same was not true of human diets. It seems we were much better at finding our preferred food, regardless of climate change or any other factor. Take a Neanderthal out of their preferred habitat and they might struggle. Not the same with us. This could have given us a key advantage over the Neanderthals, allowing us to out-compete them and ultimately drive them extinct.
Keeping our teeth sparkly white
All of this raises the question: why were humans better able to adapt to climate change than the Neanderthals? As I mentioned in the introduction, we don't have a final answer about this. But that won't stop me speculating. Strap yourself in for some hard-core hypothesising.
One popular set of explanations revolve around the idea we didn't really have an advantage. Rather, the Neanderthals were pretty disadvantaged. They had fairly bulky muscle mass and a fairly bulky brain mass too. Both these organs would have required a hefty amount of calories to fuel. Our brain isn't so big yet still takes 1/4 of our daily calories. This would have put some fairly intense pressure on the Neanderthals, perhaps making them more vulnerable to shifts in climate change. If they needed a lot of meat to keep going then that meat migrating south would have caused problems.
However, the evidence for this is somewhat circumstantial so I'm not sure I buy it. At least, not without more evidence.
Some others have pointed to technological differences between our two species. And it is certainly the case that there were some of those. However, towards the end of the Neanderthals' existence the technological gap between us was beginning to shrink. Helped by the Neanderthals nabbing out tools. Yet those groups that stole our tools still wound up going extinct. In fact, the last Neanderthals were associated with the old-fashioned Mousterian tools. So there seems to be no real correlation between Neanderthal technology and their survival.
Which brings me onto my favourite explanation: innovation.
Studies have shown that if a group of people is exposed to pressure culture is the thing that changes. This shields them from the worst of the change, stopping them going extinct. Unless, of course, you can't really change that culture. The biggest change in the Neanderthal toolkit came when they pinched stuff from ours. There was some innovation but apart from that, but it seems to have been lacking when compared to humans. Perhaps we were just better able to adapt our technology to changing conditions. When Neanderthals were the only species in Europe this wasn't much of a problem, but when we turned up things got hairy.
But like I said, this is all speculative. All we know for sure is that we had some sort of edge over Neanderthals when it came to climate change. So I guess we earn a lot of irony points by trying very hard to use climate change to kill ourselves off in the present.
tl;dr
Research reveals human diets were less impacted by climate change than Neanderthal diets. This shows we were better at adapting to changing conditions. This would likely have contributed to their extinction. Why we had this advantage remains a mystery.
References
El Zaatari S, Grine FE, Ungar PS, Hublin J-J (2016) Neandertal versus Modern Human Dietary Responses to Climatic Fluctuations. PLoS ONE 11(4): e0153277. doi:10.1371/journal.pone.0153277
Richards, M.P. and Trinkaus, E., 2009. Isotopic evidence for the diets of European Neanderthals and early modern humans. Proceedings of the National Academy of Sciences, 106(38), pp.16034-16039.
Thompson, B., Kirby, S. and Smith, K., 2016. Culture shapes the evolution of cognition. Proceedings of the National Academy of Sciences, 113(16), pp.4530-4535.
