Question of the Day

I was having a conversation with my BF the other day, and I was trying to explain to him how life evolves which eventually transformed into us reciting quotes from the Ben Stiller movie Meet the Parents...anyway somewhere in our discussion this question was raised:

Why do men have nipples?

I must confess, I have no idea. It doesn't fit with anything I know about the evolution of humans. Did men once lactate?  Or are all men sprung from women, and so retained the characteristic? I haven't done any research on it, maybe I will this weekend. But before we find out, do any of you want to theorize with me on possible answers?