Comparisons of DNA sequences between Neandertals and present-day humans have
shown that Neandertals share more genetic variants with non-Africans than with
Africans. This could be due to interbreeding between Neandertals and modern
humans when the two groups met subsequent to the emergence of modern humans
outside Africa. However, it could also be due to population structure that
antedates the origin of Neandertal ancestors in Africa. We measure the extent
of linkage disequilibrium (LD) in the genomes of present-day Europeans and find
that the last gene flow from Neandertals (or their relatives) into Europeans
likely occurred 37,000-86,000 years before the present (BP), and most likely
47,000-65,000 years ago. This supports the recent interbreeding hypothesis, and
suggests that interbreeding may have occurred when modern humans carrying Upper
Paleolithic technologies encountered Neandertals as they expanded out of
Africa