Sexual selection is one of the most interesting and weird aspects of evolution. I'll explain using an example. Suppose some women, due to random genetic variations, just happen to like men with unusually large noses. Who will they marry? Probably men with large noses. Now think about the children of these unions: They'll inherit the large noses from their fathers, and they'll inherit their mother's fondness for large-nosed men. So at the next generation, and on down through their descendants, men with small noses won't have very good luck, and men with larger and larger noses will be favored.
We see this all the time in nature. The tailfeathers of peacocks and birds of paradise, the huge antlers of moose and the elaborate dances of fruit flies are all excellent examples. We even find it in ourselves. For example, a woman's shapely figure is purely "for show." Other great apes such as chimpanzees and gorillas have no trouble producing milk without large breasts. And we men have genitals that are something like four times the size, relative to our body mass, of the other great apes. It's purely for show, and has nothing to do with our ability to have sex. The other apes do it with much smaller "equipment."
What does this have to do with the Roman Catholic Church? Everything.