Neanderthals Died Out due to Inbreeding and Bad Luck – Ancient Origins


Researchers now believe that they may have established why the Neanderthals became extinct. Expert analysts using population models believe that inbreeding and the internal dynamics of their small populations resulted in their demise. This research could mean that modern humans did not directly cause the extinction of the species of archaic humans.

The research was undertaken by a group at the University of Eindhoven, in the Netherlands and it sought to test if ‘the internal dynamics that operate in small populations’ led to the demise of the Neanderthals according to the study published in PLOS ONE . This was to establish if their decline was due to demographic factors and their mating behaviors . It appears that the global population of the species was very small and ‘was in the range of a mere 5,000–70,000 individuals’ reports PLOS ONE .

Inbreeding and demographic decline

The team used statistical tools to estimate why the Neanderthals died out. According to The Daily Mail , ‘the researchers modeled how their populations might have fared over 10,000 years’. To make their findings more reliable they also based their analysis on modern human hunter-gathering groups. They ‘ran population simulations for Neanderthal societies of various starting sizes (from 50 individuals to 100, 500, 1,000, or 5,000)’ according to Science Alert .

Male and female Homo neanderthalensis in the Neanderthal Museum, Mettmann, Germany. (UNiesert/Frank Vincentz/ CC BY SA 3.0 )

Male and female Homo neanderthalensis in the Neanderthal Museum, Mettmann, Germany. (UNiesert/Frank Vincentz/ CC BY SA 3.0 )

They first tested their population simulations with the factor of inbreeding. This can lead to an unhealthy population and PLOS ONLINE reports that they ‘had at least 40% lower fitness than modern humans on average’. According to the researchers’ findings, it played a significant role in the extinction of the archaic species of humans.

Allee Effect

The second factor, they tested is the biological phenomenon, known as the Allee effect . This is where a small population does not reproduce itself because of an inability to secure enough resources and limited choice of mates. Small populations are inherently disadvantaged when it comes to surviving in harsh environments such as the one inhabited by the Neanderthals.

The researchers, based on their models found that the Allee effect was apparent, over time. Based on the University of Eindhoven’s statistical modeling this ‘could have caused extinctions in populations of up to 1000 individuals’ reports The Daily Mail. This means that the natural attrition experienced by small populations of Neanderthals was possibly a factor in their demise.

The third factor that was modeled by the researchers was ‘was natural fluctuations in birth rates, deaths and sex ratios’ reports The Guardian . This sought to understand how a falling birth-rate and other variables could have impacted the species over a period of centuries. It was found that this was not a major factor in the extinction of the population.

Modern humans the cause of extinction?

The standard theory is that the Neanderthals were outcompeted by the smarter and more versatile modern humans about 40,000 years ago. The ancestors of modern humans arrived in Eurasia from Africa and over several thousand years this led to the demise of the Neanderthals. There is no doubt that the decline of this species coincided with the arrival ofHomo sapiens.

However, the works of the experts would seem to show that the archaic human species could have become extinct even without competition from modern humans. One of the team members who took part in the research, Krist Vaesen, stated that ‘The main conclusion of our work is that humans were not needed for the Neanderthals to go extinct’ according to The Guardian . Therefore, the arrival of modern humans may not be to blame for the extinction of the species.

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Just Plain Bad Luck?

Science Alert quotes Vassen as stating that Neanderthals may have died out ‘merely to a stroke of bad, demographic luck’. However, the team acknowledges that there are limitations to their study. They admit that modern humans could have impacted Neanderthal behavior and habitat.  The team believes that their findings can lead to a new approach to the question as to why the archaic humans disappeared.

It would appear that modern humans could still have played a role in the demise of the Neanderthals, based on the research. They could have driven the to remote and marginal lands, which could have reinforced the Allee Effect and increased the likelihood of interbreeding. Then modern humans mated with the species and this further reduced their ability to reproduce themselves. The arrival ofH. sapienscould have speeded up the process of demographic decline among Neanderthals. Science Alert  quotes Vassen, as stating that the ‘presence of modern humans in Eurasia would have accelerated a process that, at some point, was likely to have occurred anyway’

The research which argues that the small population of Neanderthals contributed to their extinction is one that could revolutionize our understanding of their fate. It may refute the idea that modern humans were culpable for the extinction of the Neanderthals. However, it seems highly likely that the debate on why these early humans vanished will continue.

Top image: Illustration of Neanderthal Man Holding Neanderthal’s Skull  Source:Roni/ Adobe Stock

By Ed Whelan

References

Krist Vaesen, Fulco Scherjon, Lia Hemerik, Alexander Verpoorte. Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinctionPLOS ONE, 2019; 14 (11): e0225117 DOI:  10.1371/journal.pone.0225117

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