Are Neanderthals Extinct Because We Were Too...

 ...sexy? Hot?

A new paper theorizes that the reason for Neanderthal extinction is that too many of them were mating with modern humans...and not with each other.

And it also notes that Neanderthal mitochondrial DNA has been lost, which might indicate that there was only one successful breeding...between a male Neanderthal and a female modern.

When breeding equine hybrids, the vast majority are mules (male donkey, female horse). Hinnies (male horse, female donkey) are much rarer because it is harder for a stallion to get a jenny pregnant. People tend only to breed hinnies when they really like the cross as it often takes several matings to be successful. And in ligers, the mating is indeed only successful in one direction. (The loss of the Neanderthal Y chromosome is indicative of a feline-type hybrid pattern, which also includes the first generation males being infertile).

Also interesting...the late Neanderthal sequences don't show any modern DNA.

Which might also tie into that if the humans that expanded into Europe were matrilocal. In a matrilocal society, you become a member of your mother's clan or tribe. Neanderthals appear to have been patrilocal in Siberia, but we don't know in Europe. It's also possible that a lot of these matings were trysts rather than longer term relationships, perhaps due to the language barrier. But the theory is that Neanderthal individuals were joining modern groups (I know that's an awkward phrasing, but both species are, in fact, human) and removing themselves from the Neanderthal gene pool.

If the vast majority of hybrids were born to anatomically modern mothers and stayed with those mothers, then our ancestors benefitted from useful Neanderthal genes...but not the reverse.

So, it's possible Neanderthals are extinct because Neanderthal men couldn't resist modern women.