Humans and Neanderthals may have some genetic similarities, but scientists suggest that sex between the two species did not occur very often.
Scientists also suggest that when sex did occur between the two species, it rarely produced a child. And even when there was a child, the hybrid offspring had trouble surviving.
Mathias Currat from the University of Geneva and Laurent Excoffier from the University of Berne published their research in the journal Proceedings of the National Academy of Sciences (PNAS).
They based their conclusions on the results of data and a computer model that suggested the interbreeding success rate was not high, MSNBC.com reported.
The model was based on DNA from modern humans in France and China and showed that intercourse resulting in a child happened less than two percent of the time, Discovery News reported.
There could have been extremely strong barriers to gene flow between the two species because of a very low fitness of human-Neanderthal hybrids, a very strong avoidance of interspecific mating, or a combination, they said, Discovery News reported.
David Reich was one of the researchers involved in the Neanderthal sequencing effort.
People today mix with people who speak their language and share similar traditions, and these groups were more diverse than modern ones, he said, Discover reported. This says to me that where modern humans and Neanderthals were in the same area of the world, Neanderthals would tend to mix with Neanderthals and humans would tend to mix with humans. I would be shocked if they mixed randomly.