Abstract
Considering the recent experimental discovery of Green et al that present-day non-Africans have 1 to of their nuclear DNA of Neanderthal origin, we propose here a model which is able to quantify the genetic interbreeding between two subpopulations with equal fitness, living in the same geographic region. The model consists of a solvable system of deterministic ordinary differential equations containing as a stochastic ingredient a realization of the neutral Wright-Fisher process. By simulating the stochastic part of the model we are able to apply it to the interbreeding ofthe African ancestors of Eurasians and Middle Eastern Neanderthal subpopulations and estimate the only parameter of the model, which is the number of individuals per generation exchanged between subpopulations. Our results indicate that the amount of Neanderthal DNA in living non-Africans can be explained with maximum probability by the exchange of a single pair of individuals between the subpopulations at each 77 generations, but larger exchange frequencies are also allowed with sizeable probability. The results are compatible with a long coexistence time of 130,000 years, a total interbreeding population of order individuals, and with all living humans being descendants of Africans both for mitochondrial DNA and Y chromosome.
Highlights
The question of whether all of us, living humans, descend exclusively from a recent (i.e. 100,000–200,000 years old) anatomically modern African population which completely replaced archaic populations in other continents, or if Africans could have interbred with these local hominids has been the subject of a long lasting and interesting debate
In the framework of the model proposed in this article we could infer that the 1 to 4% fraction [8] of Neanderthal DNA in present day non-Africans can be explained with maximum probability by assuming that the AAE and Middle Eastern Neanderthals (MEN) subpopulations exchanged only pair of individuals in about 77 generations
The mean value of the exchange parameter in the model corresponds to a much larger frequency of 1 pair of individuals exchanged in about 12 generations
Summary
The question of whether all of us, living humans, descend exclusively from a recent (i.e. 100,000–200,000 years old) anatomically modern African population which completely replaced archaic populations in other continents, or if Africans could have interbred with these local hominids has been the subject of a long lasting and interesting debate. The first of these possibilities, known as Out of Africa model, is based mainly on genetic evidence [1] further supported by palaeontological [2] and archaeological findings [3]. The model consists of the following three stochastic steps:
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