Coevolution, man. We outsourced our sense of smell to dogs a LOOOONNNG time ago, and that let us grow other parts of our brain. Might also have let us squeeze out our pesky Neanderthal neighbors.

Fascinating demonstration of the Jagger Principle:

[Laughs] The Jagger principle is, "You can't always get what you want, but sometimes you find you get what you need." Life may not be perfect, life may not be simple, but with a little luck and ingenuity you may get what you need. I regard that as a very important ecological principle.

Modern humans clearly changed something about the way they were hunting, and it was something crucial. But Neanderthals didn't change. They continued to do things in the same old Neanderthal way as life got hard and times cold. They continued to hunt the same animals with the same tools in the same way. And that lack of adaptability may have been a telling failure as these new invaders moved in. If you then add in wolf dogs, Neanderthals were at a terrific disadvantage.