1Neanderthals, throughout their long existence, occupied the regions around the Mediterranean until their disappearance between 50,000 BP and 35,000 BP (Timmermann, 2020). Since this rather rapid event coincides with the arrival of Anatomically Modern Humans (AMH) in Europe at around 46,000 BP (Hublin et al., 2020), researchers consider that AMH played an important role in the decline of Neanderthals, who were “exterminated” by the newcomers through direct or indirect competition (Tattersall and Schwartz 1999). Nonetheless, Neanderthals’ archaeological record is not sufficiently different to that of AMH and does not help explain their population decline in terms of observable inferiority (Villa and Roebroeks 2014).

2Neanderthals’ demography was modelled over the 15,000 years prior to their extinction in an attempt to understand how it “functioned”, as modelling can help explain a complex phenomenon – here, the extinction of a species as a set of simple mathematical equations. Ecological models of competition, studied and mathematically demonstrated by Vito Volterra (1926, 1931) and Alfred J. Lotka (1925, 1932), and analysed empirically by Georgy Gause (1934), were adapted, in particular, the Flores model (1998).

3Four different scenarios (A, B, C and D) were tested to analyse Neanderthal population dynamics over the last 15,000 years of their existence. The values used were taken from the literature (Tables 1 and 2). For each of the scenarios, the two extreme values of Neanderthal population size were considered: 5,000 individuals and 70,000 individuals.

	Scenario			Population size	Fertility rate	Mortality rate
	Neanderthal alone	Scenario A	1	5 000	0,141	0,4029
			2	70 000	0,141	0,4029
	Neanderthal + migrations	Scénario B	1	5 000	0,141	0,4029
			2	70 000	0,141	0,4029
	Néandertal + migrations + crossings	Scenario C	1	5 000	0,141	0,4029
			2	70 000	0,141	0,4029
	For which fertility and mortality values does Neanderthal disappear in 15,000 years?	Scenario D	1	5 000	0,001	0,3342
			2	70 000	0,001	4,6675
			3	5 000	0,141	0,4742
			4	70 000	0,141	4,8075

Table 1: Presentation of the parameters for each scenario, the origin of the values is presented in Table 2.

Parameter	Value	Source
Neanderthal population (N)	Between 5,000 and 70,000	Bocquet-Appel & Degioanni 2013
Date of Neanderthal extinction	Between 50,000 and 35,000 BP	Timmermann 2020
Period during which HAM and Neanderthal coexist	From 50,000 to 35,000 BP	Villanea & Schraiber 2019
Neanderthal fertility rate (Fn)	Between 0,1415 et 0,13	Degioanni et al. 2019
HAM fertility rate (Fc)	0,403	Bocquet-Appel 2008
Mortality rates of the HAM (Dc) and Neanderthal (Dn)	0,4029	Bocquet-Appel 2008
Interbreeding frequency	Once every 37 years	Currat & Excoffier 2011
Similarity(ies) parameter	0,998	Adapted from the equation of Flores 1998
Migrations	1 group/iteration	Kolodny & Feldman 2017

Table 2: Parameters used, values assigned and sources.

4In scenario A, Neanderthals are the only occupants of their territory during the last 15,000 years of their existence. In scenario B, Neanderthals are still the only occupants of their territory, but recurrent migrations of AMH from Africa are considered (the number of AMH immigrants is randomly drawn between 0 and 200, if this number is between 10 and 21 then a group of AMH is allowed to migrate). Scenario C allows for admixture between the two populations. Indeed, paleogenetic analyses demonstrate that a fraction of the genome of present-day non-African humans is inherited from Neanderthals (Green et al. 2010). Upon their arrival on Eurasian territory, AMH interbreed with Neanderthals and give rise to fertile and viable individuals. In this scenario, “hybrid” births are classed as AMH and the frequency of this admixture is very low, with one successful hybridisation every 37 years (Currat and Excoffier 2011). Tests of the first three scenarios, A, B and C (fig. 1), using the values proposed in the literature, show that population dynamics are such that Neanderthals do not disappear. There are only two possibilities: either the model is “unlikely" or the proposed values are incorrect.

1. Population dynamics of Neanderthals (red) and HAM (blue) over 15,000 years.

The solid line illustrates scenario A2: Neanderthals are alone on the Euro-Asian territory;
The dotted line illustrates scenario B2: small groups (less than 20 individuals) of HAM immigrate;
The small line illustrates scenario C2: between Neanderthals and HAM there is interbreeding and the newborns integrate the HAM.

5For scenario D, instead of the data proposed in the literature, different values for mortality and fertility of Neanderthals were tested, and the values retained were exclusively those that allowed for their disappearance (i.e., population size equal to 0) after 15,000 years. For a population of 70,000 Neanderthals to disappear in 15,000 years, the fertility value must vary between 0.001 and 1.141, and the mortality value between 4.8075 and 4.6675 (fig. 2). For a population of 5,000 Neanderthals to become extinct in 15,000 years, the fertility value must fall between 0.07 and 1.141, and the mortality value between 0.4029 and 0.4742.

6None of the scenarios proposed explain the extinction of Neanderthals as the result of competition between two species with almost similar needs in the same environment. For the whole population of individuals with Neanderthal traits to disappear, the values of the main demographic parameters (fertility and mortality rates) must therefore change considerably from the values selected for the implementation of our model.

2. Population dynamics of Neanderthals (in red) and HAM (in blue).

The dotted line illustrates scenario D2: very low fertility value of Neanderthals;
The solid line illustrates scenario D4: very high Neanderthal mortality value.

7Unfortunately, these results remain unsupported by archaeological data. It is possible that some parameters have not been considered and that this model is too “simplistic. Indeed, it is not spatially explicit. Consequently, the results reflect the general demographic dynamics of a population whose territory is not delimited. Moreover, Neanderthals were not a single population but lived in small groups, accordingly the values of the main parameters may vary from group to group. Finally, in this analysis, the age structure of the population was not considered and a single fertility and mortality rate was used for all age categories. Previous research has shown (Degioanni et al 2019) that a simple reduction in the fertility rate of the youngest females can have a very important impact on population dynamics.

Supplementary data

8MeN-R-Script is a compplementary data from the article Louise Ouvrard, Anna Degioanni "Modelling the extinction of the Neanderthal", Préhistoires méditerranéennes vol. 9.1|2021.
This script was written and used by Louise Ouvrard for her Master 2 project (Aix-Marseille Univ, MMSH, LAMPEA), "Extinction of the Neanderthal: the impact of crossbreeding and competition with anatomically modern humans", academic year 2020/2021.

Name

9MeN-R-Script
R-Script for a Modelling Neanderthal Extinction

Repository location

10Nakala [dataset]. Interface for depositing and managing data from Huma-Num Research Infrastructure.

Permanent link

11https://doi.org/​10.34847/nkl.fce42542
DOI : 10.34847/nkl.fce42542

creation and deposit date

12V1 created on 2021/12/09
V1 published on 2021/12/17

Dataset Format

13.txt

Software version

14RStudio Team 2020
Package used: svDialogs

License

15Etalab Open License 2.0