My theory is that quantum mechanics is what makes human intelligence an advantage in the struggle for survival.

Take Schroedinger's Cat, in a superposition of alive and dead states. The superposition is the actual state of the cat. Dealing with a cat in a superposition of states is even harder than dealing with a cat that's just alive, and much harder than dealing with one that's just dead.

But with human intelligence, we have the massive power of being able to ignore complicating facts. So we just ignore the "dead" component, simplifying the problem enormously. (It's not just that there are two components, but what about the interactions between them?)

Multiply this by all the cats in the world. You can see that dealing with all the cats in the world, each in a superposition of all the possible states a cat can be in, would be beyond any mortal creature. But the human talent for ignoring facts makes this a world in which we -- albeit barely -- can stumble from from one moment to the next.