Neanderthal genes make up 1-2% of the genomes of non-Africans. Scientists analyzed the lengths of regions of Neanderthal DNA in 58 ancient Eurasian genomes of early modern humans and determined that the introgressed genes result from interbreeding between Homo sapiens and Neanderthals about 47,000 years ago, over a single, extended period of about 7,000 years. The findings help pin down dates for out-of-Africa migration and the dispersal of Homo sapiens.