Among scientists, there is a broad consensus that modern humans played an important role in the extinction of Neanderthals: bands of modern humans would have invaded Neanderthal territory (e.g. Europe and the Near East), where they outsmarted or outnumbered their sister species
But, according to the Dutch scientists, linking the demise of Neanderthals to invasions by modern humans may have been too rash. They started from one uncontested fact: the Neanderthal population, like any other hominin population before, was extremely small, comprising perhaps no more than 10,000 individuals, and had been so throughout its existence. The researchers wondered whether that fact alone could explain its extinction.
Models
The scientists used a set of mathematical and computer models from conservation biology to represent Neanderthal populations. They then let these populations undergo three processes that small populations are particularly vulnerable to: inbreeding, difficulties in mate-finding, and random fluctuations (in mortality and reproduction). To their own surprise, the team found that even if Neanderthals had been fully identical to modern humans, they faced, over time, a considerable risk of extinction, and this merely due to their small population size. This suggests that no invasion of another species, let alone a superior species, was needed for them to vanish from the face of the earth. Neanderthals might simply have been unfortunate to have lived in small numbers.
Comment: The archeological evidence shows that Neanderthal technology "stagnated" for possibly 150,000 years, quite unlike the sometimes rapid and consistent innovation seen in the human population. Further data, like the absence of sophisticated cave art supports the fact that Neanderthals were quite unlike humans and were possibly at a disadvantage, overall, in this sense.
The Neanderthals became extinct some 40,000 year ago. This begs the question why it took almost 400,000 years for them to disappear. According to Krist Vaesen, associate professor at the School of Innovation Sciences at Eindhoven University of Technology and one of the authors of the paper, this may simply have been bad luck. "Small populations can survive over long stretches of time, and then suddenly disappear due to random fluctuations in births, deaths, sex ratio, and environmental pressures."
Does this mean that modern humans played no role in the demise of Neanderthals? "Not necessarily", says Vaesen. The researchers leave open the possibility that the invasion of modern humans speeded up the process of decline. Such a scenario could indeed be one in which Homo sapiens outsmarted or outnumbered Neanderthals. "But", Vaesen adds, "our results suggest another plausible scenario: a peaceful co-existence of the two species, a scenario in which the mere presence of bands of modern humans reduced the opportunities for Neanderthals to find mates, intra-breed and migrate."
Null hypothesis
The researchers see the results of their study as a null hypothesis against which other explanations need to be assessed. "Regardless of whether external factors or resource competition played a role in the extinction of Neanderthals, our study suggests that any plausible explanation also needs to incorporate demographic factors as key variables".
The paper 'Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinction' by Krist Vaesen, Fulco Scherjon, Lia Hemerik and Alexander Verpoorte was published in PLOS ONE on [date].|DOI: [xxx]
Comment: It seems increasingly likely that a multitude of factors led to the demise of the Neanderthals, but, as of yet, genocide by humans is not supported by the evidence.
If, after a period of relative stability in the Neanderthal's environment, along came ever increasing pressures of a shifting climate - and all the challenges that poses - as well as with more sophisticated species on the scene, could it be that Neanderthals were simply unable to adapt to these new challenges? Humans, as shown by their proliferation across much of the planet, are capable of adapting to all kinds of conditions, whereas Neanderthals, as reflected in the "stagnation" in tool design, small population sizes, their limited scope of habitation throughout Europe, were not. And so, naturally, like many other animal species, including other hominin species, isn't it more likely that Neanderthals, more simply put, no longer 'fit', and, in turn, died out?