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, 14 (11), e0225117
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Inbreeding, Allee Effects and Stochasticity Might Be Sufficient to Account for Neanderthal Extinction

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Inbreeding, Allee Effects and Stochasticity Might Be Sufficient to Account for Neanderthal Extinction

Krist Vaesen et al. PLoS One.

Abstract

The replacement of Neanderthals by Anatomically Modern Humans has typically been attributed to environmental pressure or a superiority of modern humans with respect to competition for resources. Here we present two independent models that suggest that no such heatedly debated factors might be needed to account for the demise of Neanderthals. Starting from the observation that Neanderthal populations already were small before the arrival of modern humans, the models implement three factors that conservation biology identifies as critical for a small population's persistence, namely inbreeding, Allee effects and stochasticity. Our results indicate that the disappearance of Neanderthals might have resided in the smallness of their population(s) alone: even if they had been identical to modern humans in their cognitive, social and cultural traits, and even in the absence of inter-specific competition, Neanderthals faced a considerable risk of extinction. Furthermore, we suggest that if modern humans contributed to the demise of Neanderthals, that contribution might have had nothing to do with resource competition, but rather with how the incoming populations geographically restructured the resident populations, in a way that reinforced Allee effects, and the effects of inbreeding and stochasticity.

Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Inbreeding and stochasticity.
Irisk (lowest value of inbreeding depression parameter I that results in at least one extinction event in ten simulation runs) and Isure (lowest value of inbreeding depression that results in extinction in all simulation runs) for various initial population sizes N0 and fi = 50% (for fi = 30;70, see S1 Appendix). The horizontal dotted lines mark the range of values of I observed in AMHs.
Fig 2
Fig 2. Allee effects, with and without stochasticity.
(a) Arisk (lowest value of Allee parameter A that results in at least one extinction event in ten simulation runs) and Asure (lowest value of Allee parameter A that results in extinction in all simulation runs) for various initial population sizes N0. (b) Birth intervals corresponding to Arisk and Asure, as well as birth intervals corresponding to the Asure values obtained in the non-stochastic matrix model (labeled Asure(MM)). The horizontal dotted lines mark the range of values of birth intervals observed in contemporary hunter-gatherers.
Fig 3
Fig 3. Inbreeding, Allee effects, and stochasticity.
Arisk (lowest value of Allee parameter A that results in at least one extinction event in ten simulation runs) for a scenario without inbreeding (blue triangles; Arisk(0)) and a scenario with inbreeding (orange squares; Arisk(3.2)) (inbreeding depression parameter at I = 3.2).

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Grant support

Research by KV was supported by the Netherlands Organisation for Scientific Research (NWO) (grant 276-20-021).
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