I saw a documentary about how the neanderthals may have died out. According to one theory tha Neanderthals were more muscular had shorter legs and had no waistline. they lived in forest areas. They hunted with heavy spears and crept up on the animal being hunted. The spear was not thrown but thrust into the animal at close quarters.
The forests were decreasing during an ice age and open plains were increasing.
The theory is that modern humans started to inhabit the open plain areas because they were more athletic and were using a light spear which was thrown. Usually an animal runs quite a distance especially when a lighter spear hits its intended targetso even after the hit modern humans may have to run quite a distance to take down there quarry. The Neanderthal was just not athletic enough for this new type of hunting.
Did they interbreed? No! They kept their penis in their genis