Neanderthal - Interbreeding Hypotheses

Interbreeding Hypotheses

An alternative to extinction is that Neanderthals were absorbed into the Cro-Magnon population by interbreeding. This would be counter to strict versions of the Recent African Origin, since it would imply that at least part of the genome of Europeans would descend from Neanderthals.

Hans Petter Steensby, while strongly emphasising that all modern humans are of mixed origins, proposed the interbreeding hypothesis in 1907, in the article Race studies in Denmark. He held that this would best fit current observations, and attacked the by then widespread idea that Neanderthals were ape-like or inferior.

The most vocal proponent of the hybridization hypothesis is Erik Trinkaus of Washington University. Trinkaus claims various fossils as products of hybridized populations, including the "child of Lagar Velho", a skeleton found at Lagar Velho in Portugal dated to about 24,000 years ago. In a 2006 publication co-authored by Trinkaus, the fossils found in 1952 in the cave of Peștera Muierii, Romania, are likewise claimed as descendants of previously hybridized populations.

Genetic research has confirmed that some admixture took place. The genomes of all non-Africans include portions that are of Neanderthal origin, due to interbreeding between Neanderthals and the ancestors of Eurasians in Northern Africa or the Middle East prior to their spread. Rather than absorption of the Neanderthal population, this gene flow appears to have been of limited duration and limited extent. An estimated 1 to 4 percent of the DNA in Europeans and Asians (French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with Sub-Saharan Africans (Yoruba and San probands). Nonetheless, more recent genetic studies seem to suggest that modern humans may have mated with "at least two groups" of ancient humans: Neanderthals and Denisovans.

While modern humans share some nuclear DNA with the extinct Neanderthals, the two species do not share any mitochondrial DNA, which in primates is always maternally transmitted. This observation has prompted the hypothesis that whereas female humans interbreeding with male Neanderthals were able to generate fertile offspring, the progeny of female Neanderthals who mated with male humans were either rare, absent or sterile. However, some researchers have argued that there is evidence of possible interbreeding between female Neanderthals and male modern humans.