This definitely ties in with the body image issue. Not only does our culture have a very narrow range of body shapes that we need to fit to be acceptable, but there's also a very narrow window of what makes us 'pretty' on the surface. There is a seemingly innate need for girls to feel like they need to meet that standard and it is more important than other traits that can ensure better survival (e.g., intelligence, resourcefulness, compassion).
Here is Katie Makkai talking about 'pretty' poetry slam style. Enjoy!