Genetic vulnerabilities among the possible causes of Neanderthal extinction

Artist's portrait of a Neanderthal (Image courtesy Petr Kratochvil (CC0))
Artist’s portrait of a Neanderthal (Image courtesy Petr Kratochvil (CC0))

An article published in the journal “PLOS ONE” reports a study on the causes of Neanderthal extinction based on models created using data on hunter-gatherer populations as parameters. A team of researchers led by Dr. Krist Vaesen concluded that small populations were vulnerable to problems such as inbreeding, the Allee effects that predict a negative impact on individuals’ fitness in reduced populations and demographic fluctuations, factors that over about 10,000 years caused the extinction of this species.

The extinction of the Neanderthals is one of the great enigmas in the field of paleontology and in particular of paleoanthropology. In recent decades, it’s become clear that the stereotypes spread with the first Neanderthal reconstructions in which they were seen as ape-like are wrong and that this species had more or less the same intellectual skills as Homo sapiens. However, about 40,000 years ago these hominins became extinct, although the success in finding DNA fragments in various Neanderthal bones made it possible to ascertain that there were interbreedings with Homo sapiens and that for today’s Europeans it’s normal to have some genes of Neanderthals.

One of the most controversial themes in discussions about the extinction of Neanderthals is the possible role played by Homo sapiens. The competition for resources by the Homo sapiens who were migrating to Europe and the Middle East at a time when the Neanderthal population was shrinking dangerously is considered an important factor by many scientists, but there are some who even suspect genocide. Now the team led by Dr. Krist Vaesen from Eindhoven University of Technology and the University of Leiden carried out computer simulations to try to understand if the Neanderthal populations could have disappeared without external factors.

The researchers used models based on hunter-gatherer populations existing today, which meant using data on populations of Homo sapiens living in today’s environmental conditions. However, that’s an approximation that should be good because some problems related to inbreeding are taken into consideration in a species similar to Homo sapiens. Small populations with groups ranging from 50 to 5,000 people were simulated. The simulation included the effectss of inbreeding, the Allee effects with a negative impact on individuals’ fitness in the small population and possible demographic fluctuations due to variations in births and in deaths and sex ratio.

The results of the simulations indicate that inbreeding is unlikely to have been the sole cause of Neanderthal extinction. Allee effects with a decline in births may have led to extinction in populations of no more than 1,000 people. Other demographic fluctuations may have negatively affected Neanderthals over millennia.

The possible impact of the growing populations of Homo sapiens is difficult to assess. It’s possible that Neanderthal populations interbred with modern humans decreasing the between different Neanderthal populations, increasing the risks of genetic stagnation. The comptetition for resources between Neanderthals and Homo sapiens remains a serious possibility as a cause of Neanderthal extinction.

At some point in the history of the Neanderthals, their population formed by isolated groups was vulnerable. That’s a situation in which a population can survive for a long time and then disappear due to a negative event, where a genetically less vulnerable population would have survived.

This research suggests a solution to the enigma of the extinction of the Neanderthals but it’s far from final. In the last 100,000 years other species of hominins have become extinct so the studies could be more complex. Homo sapiens could be the species that best adapted to the environmental changes that occurred in those millennia managing to occupy more and more areas in which before there were other hominins.

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