This "paradox" seems to me to be inherently wrong anyway, it makes the assumption that women have always been free to choose who they marry, which of course is blatantly not the case. It also of course neglects the impact of women choosing to marry for reasons other than looks, money being the obvious example.
Regardless of this, the researchers Professor Marion Petrie and Dr Gilbert Roberts of Newcastle University believe they have found a mechanism that explains why we are not all models.
The scientists claim that since genetic mutations can occur anywhere in the genome, some will affect the DNA repair kit possessed by all cells.
As a result, some individuals have less efficient repair kits, resulting in greater variation in their DNA as damage goes unrepaired.
This variation leads naturally to a variation in looks, it probably has other effects which are more beneficial to the population, like providing a wide range of mutations some of which could be useful in fending off disease for example. In other words it looks like there is a balance in a population between everyone looking good and having a wide enough variation in the population to be able to resist changes in the environment. Exactly as natural selection would predict.