[Kenny Bunk]

That Neandertals and Cromagnons interbred is, IMNVHO, an established fact. Now the question becomes, "How well and how often did they interbreed?" Was the half-breed hybrid offspring successful? As a hybrid a Neandertal/Cromagnon cross might have been mostly sterile, like a horse/donkey cross. Maybe a few of the hybrids were able to breed, but bred with other Cromagnons, diluting the DNA.

E.G., they have spent years trying to crossbreed cattle and buffalo. Looks as if it would be easy, right? So nowadays, we are a modern human/Neandertal hybrid, but the Neandertal DNA is down to just a trace. So, like horse and donkey, we remain two separate species, and with just a trace, we identify with the Mod Hums.

PS:
Warning. All I know about anthropology and Paleontology, I learned from Red Badger and from the pamphlets in a Holiday Inn Express suite.

[Scoutmaster]

and from the pamphlets in a Holiday Inn Express suite.

Laz? That's where you left them.

[Nepeta]

That Neandertals and Cromagnons interbred is, IMNVHO, an established fact. Now the question becomes, "How well and how often did they interbreed?" Was the half-breed hybrid offspring successful? As a hybrid a Neandertal/Cromagnon cross might have been mostly sterile, like a horse/donkey cross.

Given the prevalence of Neanderthal DNA in world populations, the hybrids were anything but sterile.

[Verginius Rufus]

I think the differences between horses and donkeys are much greater than between Neanderthals and Cro-Magnons. If I remember rightly, horses and donkeys have different numbers of chromosomes.

How did Neanderthals and Cro-Magnons interbreed? Sounds like a topic for a federal research grant. "Hey, baby, want to see my cave paintings?" Did Cro-Magnons need beer goggles?