The NYT has an interesting article about a theory that I’ve always thought to be true (but now has, you know, evidence). Actually, I would say my opinion was heavily swayed by Howard Bloom’s book, The Lucifer Principle.
What we think of as good and evil – the basis for the modern understanding of morality – is for a large part decided by natural selection. There are many reasons why we don’t go around killing each other, not the least of which is that what’s good for the group is generally good for the individual. This is not because God said so, but because we have learned that the group can help us, protect us – and we should therefore protect it. Mr. Bloom goes into much greater detail and cites countless scientific studies to back up his claim that what we would call good and evil are in fact the by-products of some evolved trait. I highly recommend the book.
This also goes to dispute the claim that mankind needs religion to act morally. We have evolved to who we are because it works – it seems a blatantly obvious thing to say, but it is something that many people (because of their taught reverence for religion) have never considered.