Natural selection is a great example for more than one reason: Darwin wasn't the very first to think it, but Origin of the Species is perhaps the most beautiful science ever written.

Darwin actually held back Origin species for more than ten years because it clashed with his religious beliefs. He only released it when Alfred Russell Wallace sent him a letter asking him to look through a new theory on evolution, which of course was the exact same one that Darwin had come up with many years before.

And yes I agree with you - the implications of this theory are so broad that with a bit of stretching it can probably explain the whole field of psychology. An amazing insight.