Many people agree with you. It's the whole When Harry Met Sally debate. I don't think it's written in one's DNA, however. I would posit that it's a learned behavior. Women don't befriend men we're hoping to be in a relationship with because we don't see friendship that way. Men, however, don't usually have the same kind of friendships women do and think it's perfectly acceptable to act like a friend while having ulterior motives. If my lesbian friends can be friends with me without sex on their minds, I'm pretty sure straight men can do it, too. I don't think it's coded in our DNA. I think it's accepted in society. But what if we taught boys the difference between true friendship and romantic relationships and the benefits of each? It might make for a different society with women feeling less used by men who only ever pretended to be a true friend.