Here’s a hypothesis that I haven’t seen elsewhere: More beautiful women will be found in monogamous cultures, or among monogamously-inclined races.
Where women don’t (or can’t) sleep around, and where men are expected to assume a heavy economic and emotional responsibility for the women they woo, men will be choosier about the women they date and marry. Monogamy selects for male choosiness.
If you’re a man, and you’re limited to dating only a few women in your lifetime, and there are onerous familial and cultural pressures to marry the first or second woman you date, you are not going to throw away your one shot at a girl — not to mention all those resources you accumulated to win her over — on an Amanjaw Marcuntte. You’ll take your time assessing the available female goods, and aim for the hottest babe you can get. You’ll waste little time or energy spelunking slutty fat chicks or mustachioed feminists.
Over eons, this results in the more monogamous races and cultures of humanity producing more beautiful women. Of course, seismic shifts in the mating market have been underway for the past 60 or so years, so I expect a future of less beautiful women, on average and proportionate to their overall numbers, compared to the recent past. The one exception to this uglification trend will be the total bifurcation into a female beauty oasis of the 1% ruling class from the Gorgonian masses.
Relatedly, I am familiar with the theories that cad societies where men hypervigilantly (and hyperjealously) guard their women from alpha male interlopers, and geographic regions where high parasite loads influence the sexual selection process so that beauty — a sign of health and lack of genetic mutations — is favored, produce more beautiful women.
Arguing somewhat orthogonally to my monogamy-male choosiness theory is the theory that skewed sex ratios which favor men would produce more beautiful women over the generations. Such societies would be notable for their polygyny, de facto or de jure.
Perhaps all these theories reinforce each other, such that we would find the most beautiful women in countries with established monogamy norms, higher parasite loads, and sex ratios favoring men (caused predominately by men dying young, or otherwise taking themselves out of the sexual marketplace). Where we won’t find the most beautiful women, or any halfway-decent looking woman, is among the readership of Jizzebel or Feministing. Their high parasite load is offset by their self-selecting loserdom.