You don’t suppose that widespread adoption of same-sex marriage among Neanderthals might have had something to do with their ultimate downfall and disappearance, huh...
Some hold that the Neanderthals were harem-keepers and that Modern Man did them one better by pioneering the nuclear family structure.
Physical evidence cannot tell one way or the other, however.
Also a mystery is the artistic/technological explosion among humans about 40,000 years ago. Modern humans did not seem to live any differently from the Neanderthals until that moment.
Alien monoliths, anyone?