Link: Why women have breasts

From the article:

In peacocks, however, the males are the pretty ones. In humans, somehow this is reversed: women are the pretty ones, and men are all astonishingly ugly. In most species, the females are the replicators, and must be sensible about camouflage and the like, and so can't afford to be showy, but even if most of the males die because of their hampering plumage, this doesn't matter, since those left can fertilise all the females, and will probably have the best genes anyway, since they managed to survive. This occurs in its most extreme form in species where the males play little or no part in the rearing of offspring. Humans have fairly high male parental investment, however, and so the males are more valuable, and as said before, mortality due to predation in adult females, even those hampered by udders, would be so low, that this rule could in humans be sex-reversed.