We were learning about the skeleton in class the other day and something I found really interesting was that there are actually differences between male and female skeletons.
Particularly in the pelvic region, obviously because the woman has to carry children. I think the lecturer basically said that if they were any wider, the woman wouldn't be able to walk upright and if they were any thinner the head of a newborn wouldn't fit. Unfortunately, thinner means being able to run faster.
He did point out that there was a particular kind of leg crossing that women can do because of the wider pelvis that men cannot, so I guess we get some perks.