Evolution is not quite as easy as everyone assumes it is. I don't know much about it myself, but I do know enough to know that I can't appeal to it to make arguments about human nature.
Evolution, at its core, strives for only one thing: propagation of the species. Taken to this level, it's a wonder that everyone isn't spending their time either at drunken orgies, or fighting each other to get into the drunken orgies. Somehow, "civilization", "culture", and "society" have guided human development away from that model - and I don't presume to know how it happened.
Taken to the extreme, why have we even developed arms, legs, eyes, ears, and minds? Simple bacterial reproduction does just fine. In fact, there is so much bacteria in our gut and sinuses that 90% of the DNA molecules in our bodies are foreign. One begins to wonder, then, whose purpose our human bodies really serve.