My impression is that most mammals function in a like matter. We know or should know that sexual climax releases endorphins, a natural high. The act and climax along with intimacy is highly desired by most of us. But in a pinch climax is enough. Evidence is that most people engage in sex on most occasions for enjoyment, not procreation, but the official reason is that "nature" induces us to engage in sex for the purpose of procreation and continutaion of the species. We also know that humans are attracted to the opposite gender based on appearance we call "sexy", but are also known to help the species procreate and be successful. There for a certain proportion in women, including child bearing hips that without thinking about it, men find desirable. Strong virile or men who have personal wealth has traditionally been a desirable trait women look for to have strong healthy children, or to ensure their personal security during child raising years. I've noted that the latter (possession of wealth) may be reversing genders as more women become the bread winners of the family and instead of having a biological basis is probably just cultural common sense. How did these characteristics become part of our make up? Do animals engage in sex because they know they are procreating or are they just being lured by the pleasure of sex? It can be argued that without this incentive, most mammals are not thinking about procreating, and would not engage in such activity just for that purpose (procreation), or would they? So the question is wow did these mechanisms get established in organisms? I have no idea. I know what is. I just don't know how such things developed. Any biologists on the forum who'd care to comment? Here's an interesting article about Why We Have Sex at Psychology Today. Enjoy!