Also, maybe the reason marriage drains the desire for sex outta women is cause we're actually not built for monogmy. The whole idea only arose as a way to control land and keep property on for future male offspring. The idea being all the virile young thangs went for the Man Who Could Provide. Usually by being the best (or adequete enough) hunter etc. So some wiseguy thinks "hell I sure had to work hard to get this broad (do people actually use that word) why not make things easier for my offspring by constructing a system whereby this woman is bound to give sex only to me-thereby causing no confusion as to which one of us guys leaves his favourite spears/other bits of accumulated wealth, and giving my future offspring a headstart in the game of Better PROvider.