Neanderthals and non-African modern humans interbred 49,000 to 45,000 years ago. Only 2% of our DNA comes from Neanderthals. A recent paper by Alexander Platt, Daniel Harris and Sarah Tishkoff looked at the distribution of these segments and found that they’re depleted on the X chromosome. Their simulations suggest that the best explanation is that most of the inbreeding was between Neanderthal men and modern human women. As Bridget Alex writes, it was likely a matter of mate choice: Either modern human females fancied Neanderthals over their own kind, Neanderthal males preferred modern females, or both.
Note: Are Neanderthals and human the same species? Technically yes, since they interbred. Still, they have two distinct names: Homo sapiens and Homo neanderthalensis. While I think “humans” should include Neanderthals, I made an exception for the title of this post since the alternatives such as “anatomically modern humans” to refer to non-Neanderthal humans are too clunky.
Nehaveigur 