This next case study is rather intriguing, and I'm inclined to agree with it.
If more attractive parents have more daughters and if physical attractiveness
is heritable, it logically follows that women over many generations gradually become more physically attractive on average than men.
"In men, by contrast, good looks appear to count for little, with handsome men being no more successful than others in terms of numbers of children. This means there has been little pressure for men’s appearance to evolve.
More here from the Times Online.
The only problem with this hypothesis is that there has to be a set definition of what "beauty" is. And that, as they say, is in the eye of the beholder.