First, the question:
@gregory Dyke asks: "A tongue in-cheek question to balance out the overly serious nature of the past few discussions. Is the theory set forward in http://www.youtube.com/And here is my initial response:watch?v=Jqmd75VsVFU @1.30 correct? Beauty and good dancing in women are linked because men do the asking, are shallow and therefore invite the beautiful women, thus affording them more opportunity to dance and become good?"
Holy long response that I just typed out and have decided would be a better blog post. Short answer: as an evolutionary biologist, this theory (as in, prettier girls have more OPPORTUNITY to become better dancers because they'll get asked more often at the beginning) is totally plausible and would not require a large bias at all. A very small (or unconscious bias) would be plenty sufficient. As a follow whose default look is butch and scruffy but who can clean up to what might be described as glamour tomboy, I can say that when I make more effort to look more attractive, I get more dances, hands down.
But here is my slightly more complete response....