If you study psychology and sociology, you will find the answer.
my cliff notes response, is that we learn our values, from those around us and the influences in your culture.
Beauty, religion, morality, sexuality, appetite, and practically everything else in your life comes from others.
Parents, uncles, aunties, friends, those you spend time with, and look up to.
I have dozens of friends and family that are perfect examples of this phenomenon. Look around you, I'm sure you can find patterns, if you know where to look, and what to observe.
I have nieces that are obessed by 'hot' guys, and will do anything to try and get their attention. And guess what? Their mother is always reading National Enquirer, People, and watching e! TV and Entertainment Tonight. That is the household they grew up in. The mom is always talking to them about which celeb just got implants, and who's trading up and dumping whom, etc. See the correlation?
Then I have other nieces, who, were home schooled, they didn't own a TV, and so had little media influence for much of their youth. They went to church regularly, and now, the are studying to be a doctor and vet. They are kind, polite, take care of their grandma, and are the sweetest girls in our family. And guess what? They are slender, tall and very attractive. Except they wear glasses (easily solved by contacts).
I can give other examples of nephews, friends kids, and more, but I'm trying to keep it short here.
Of course, just like in nature and biology, you will always find exceptions, (like hermaphroditic fish that can be difficult for scientists to categorize in taxonomy, the hibiscus flower, marsupials, etc.), but as in science, you can make some broad generalizations, and find that it is a 'rule of thumb' that will apply to most situations.
So that is the explanation for you, who was asked the 'pretty' question, by the girl.
But the response you want to give to THAT girl, that you might have used, if you were quick to the draw, could have been a quip such as:
- not me, i like them fat and fugly, (thats why I hang wit u), :o
- for the same reasons that girls go for guys; [with] money, power, fame,
- its in the male genetic potential, to find a attractive mate, 'survival of the fittest,'
- men are more visual than women, women are more emotional, like peacocks, but in reverse,
- its more fun that way, after all, who wants to be with a 'fatty?!'
- and probably a hundred other one liners.
Hope this helps.