I once read about a study in which thousands of heterosexual men were given a bundle of photographs of women and thousands of heterosexual women were given a bundle of photographs of men and all were asked to assess the attractiveness of each person depicted.
This produced a consensus list of the most to least attractive man and most to least attractive woman.
When those lists were put side by side it produced a near perfect list of men and women who were couples; that is, those running the experiment had collected pictures of people who were in couples, had separated them into random bundles of pictures of men and women, and – indirectly – collected opinion had ordered them all back into couples.
So, it would seem, unattractive people are not less likely to reproduce: they are simply unlikely to reproduce with attractive people; attractive people will be reproducing with attractive people and unattractive people will be reproducing with unattractive people.
[I’m sorry to say that I cannot now find the report.]
Attractiveness can vary a lot on cultural norms and on who you ask. If you look at, for example, art through the ages meant to depict ideals of beauty, you will find that over time, the ideal image of beauty will keep changing, and different cultures have different standards for beauty.
Also, there isn’t a single “attractive” gene. Facial features and whatnot are controlled by many different genes, and putting two attractive people together does not necessarily mean that their offspring will be attractive, and the same goes for putting two unattractive people together.