My theory on looks:
Believe or not, I doubt that we're as advanced as we think. Humans still have the same primitive wants as all animals: food, shelter and sex.
In the animal kingdom, they would pick their mates on physical features. The strongest, or the fastest or whatever. This is because the stronger or better mates are usually the best at breeding and protecting. I think that this physical attraction remains in human, and proves that perhaps guys are less evolved then girls (maybe?). This is why guys like the shape of girls (big hips = good mother), and are generally obsessed with size.
Another theory I have attached to this, is that girls who are sexier, or more attractive, would be more fertile. Of course, I'm not a scientist and there's probably no moral way to work out if this is true, but it'd still be interesting to work out.