From a science PR, “Neandertals Probably Not as Rigid in Their Diet as Thought”:
One hypothesis suggests that Neandertals were rigid in their dietary choice , targeting large herbivorous mammals, such as horse, bison and mammoths, while modern humans also exploited a wider diversity of dietary resources, including fish. This dietary flexibility of modern humans would have been a big advantage when competing with Neandertals and led to their final success.
It’s certainly an interesting hypothesis. It assumes that Neanderthals would never in a million years have considered eating fish even if they were starving, whereas current modern humans would eat frogs and insects if they had to.
Underlying such a thesis is an unjustified assumption about how Neanderthals’ brains worked (“rigid,” an assumption that the authors of such a thesis were not likely asked to justify). The authors would not be asked to justify the thesis because the underlying doctrine of Darwinism implies that there were once many other human species whose brains did not work like ours, and they went extinct (or we extinguished them). And maybe they starved to death because they wouldn’t even think of eating fish? The Neanderthals suit the Darwinian view insofar as their type is extinct and thus can’t disprove it. But all the rest is conjecture. And now:
“This study provides indirect support to the idea that Middle Palaeolithic Hominins, probably Neandertals, were able to consume fish when it was available, and that therefore, the prey choice of Neandertals and modern humans was not fundamentally different,” says Hervé Bocherens. He assumes that more than diet differences were certainly involved in the demise of the Neandertals.
It is just as reasonable to believe that their demise as a group was simply the result of melting into the modern human population, however violent or otherwise the circumstances in different cases.