The quantity of gametes produced by and the possible reproductive frequency of each gender are grossly disproportional. As a male I am (theoretically) fertile at all times from puberty until I die and am not biologically constrained to fathering children once every nine months. Social stigmatization, morals, ethics and child support aside, I am want to spread my seed as much as possible. Women, however, are relatively constrained in their ability to reproduce and it is much more expensive for them. Not to mention it being historically dangerous for them (not from fundamentalists, but from death in childbirth).
So biologically women are generally more selective about who they mate with. However, that doesn't mean that male-dominated societies haven't attempted to tip the scales in their favour somewhat.