Why the Neanderthal went extinct.

Bottom line - longer tendons and not enough trees.

Our ancestors evolved as cursorial hunters on the open lands of Africa, where they would simply chase animals into exhaustion.  In the European forests, chasing animals into exhaustion wasn't going to happen, so Neanderthals became ambush predators, learning to fight animals at close quarters.  As the glaciers advanced, Europe became unforested tundras, just as our ancestors were evolving.

But for that ecological change, Europe might still be in the hands of a species of humanity that would win every Olympic contest involving strength.