"Would they have recognized each other as possible mates?" Harvati asked. "We know when closely related primate species meet, they sometimes interbreed in nature, not just in zoos, and this is something we see not just in primates, but with other closely related species among mammals."
That the least of it. Human beings have been known to have sex with just about anything animal, vegetable, and mineral. Some human beings like corpses while others prefer cows, goats, or dogs. The producers of one popular movie were so proud of the sex Jason Biggs had with an round-shaped apple dessert that they named the movie American Pie.
If homo sapiens lived at the same time as Neanderthals, there can't be much doubt that there was a fair amount of sex between members of the two groups. The only real question is whether the sex could have resulted in pregnancy.
At an October conference in Cold Spring Harbor Laboratory in New York, Pääbo — a
geneticist of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany — said the two species had sex, but it remained an open question as to
whether children resulted and left a legacy in our genomes.
A very open question.