Advertising agencies live by the aphorism that sex sells because it's one of the most basic, driving forces in our lives. Getting it, however, is a different matter altogether. In the animal kingdom, males and females of many species are known to trade resources for sex. Humans are no different. In the most basic terms, men can be said to offer protection to females, while females offer the promise of offspring to the males (we're talking caveman mentality here; let's leave the modern societal norms aside for a moment).