Neanderthals are three times as different from us as we are from each other ... ~ Chris Stringer
It has become standard fare in the pop science media to portray the extinction of Neanderthals as being, in large part, due to the arrival of Homo Sapiens, because we sapiens were just so much smarter and clever and ruthless and good looking. Okay, maybe not that last. Now, it seems that detective work into Neanderthal mitochondrial DNA has indicated that they were pretty much doomed without our assistance.
There is no doubt that Neanderthal got a bad rap for years, based mostly on conclusions drawn from one set of bones. Those bones conjured up an image of a stooped, thick-browed caveman who was barely smart enough to get out of his own way. It turned out, of course, that the bow-legged, bent frame suggested by the bones in fact belonged to an elderly Neanderthal afflicted with arthritis. Later discoveries showed that Neanderthal most likely was put together more like a body-builder.
It also appeared that Neanderthal society was a little more complex than first thought. They buried their dead with grave goods, for instance, not something you'd expect from a stupid cave man. This sort of burial implies a belief in an afterlife, which takes the beginnings of a searching mind.
Along comes Cro-Magnon man, and Neanderthal, after chugging along for a quarter of a million years, drops off the face of the Earth. Conclusion: Cro-Magnons kicked Neanderthal butt. Or, if you prefer, Neanderthals and Cro-Magnons interbred to lead to the mess that we are today.
Well, maybe not. To begin with, studies of Neanderthal DNA have pretty much ruled out that they are in any way our ancestors. As to getting wiped out by Cro-Magnon, Chris Springer is quoted in the linked article as pointing out that there weren't many Cro-Magnons yet, so it's entirely possible they never even made contact. If they did, it's unlikely there was any large-scale warfare of extinction.
Because the populations were so small, it's also unlikely that Cro-Magnon somehow was using up scarce resources. In other words, there were plenty of animals for both of them. The conditions were changing so Cro-Magnon may have adapted better than Neanderthal, but the newcomers weren't taking the food out of the mouths of the cavemen.
Population size, however, is the nub of the matter. According to the study, Neanderthal populations were small. The mitochondrial DNA shows that Neanderthal was more prone to harmful mutations than modern humans; normally these would be weeded out as population grew. But Neanderthal population wasn't growing, so the mutations had a deleterious effect, perhaps affecting their immunity to ailments or their ability to process nutrients. Whatever it might have been, Neanderthal was doomed because their numbers were always relatively low.
No explanation is offered for why they never reproduced rapidly enough to be able to overcome the negative mutations, but low population may account for another thing that has always bothered anthropologists.
Neanderthal, as I said, was around for around 250,000 years. At the end of that time, they were using basically the same tools and methods that they were using in the beginning. Compare that to the progress made by Homo Sapiens in a 100,000 year span, and I'm not talking about space flight. Early modern humans discovered farming, domesticated animals, developed spear throwing implements, and continuously improved their stone tools.
Here's Neanderthal, with a brain as big as ours (in fact, slightly larger), which appeared to be basically wired the same as ours, yet they stagnated. One theory used to claim that Neanderthal didn't have the power of speech, but recent discoveries of hyoid bones would indicate that they could have spoken. Whether they did or not is still open to debate, but it's hard to imagine that they did not. They appeared to be good hunters, which implies some sort of communication.
A new mathematical model of population versus innovation might provide a clue. According to the model, given an increase in population and an intermingling of different communities can spur innovation. Now, I've often expressed my concerns about mathematical models and computer simulations, so I would suggest that this one should be taken with a grain of salt. But, it does promote an plausible scenario for the demise of Neanderthal.
Consider this: Neanderthals were spread across Europe in small numbers. They probably seldom crossed paths to exchange ideas. As their numbers dwindle, such interactions, if they occurred at all, became almost non-existent. Because of their small numbers, they don't even stumble across Cro-Magnon groups much either. Then the climate chilled and dried, causing game to move from the accustomed areas. Okay, Neanderthal was probably smart enough to move with the herds, but the worsening weather causes disease to have a greater effect on the health of individual Neanderthals, making it harder to muster a long hunt.
Basically, Neanderthal got weaker and more isolated, a recipe for demise. It's a very plausible scenario.
Because Neanderthal lasted so long, they're often referred to as a very successful species. But, they didn't prosper, they merely survived. While that's not exactly chopped liver, it's not a long term recipe for success.
We modern humans, who have been around for half as long as the Neanderthals were, should keep that in mind.