Já pela "teoria nórdica" acho que o esperado seria que a pele tendesse sempre a clarear sempre que possível, o tanto quanto for possível. Parece bastante razoável esperar que fossem mais ou menos todos como os khoisan.
Buckaroo, você está criando um espantalho, Frost não afirma que caracteres de tipo ''nórdico'' sempre irão surgir nas populações do jeito que você está afirmando, tampouco diz que existe uma tendência a se clarear a pele onde quer que haja seleção sexual. Sua teoria afirma que devido a grande disparidade existente entre homens e mulheres (existiam muito mais mulheres) na Europa do Norte, algumas mulheres desses locais desenvolveram caracteres mais atraentes aos homens e esses caracteres foram passados adiante por seleção sexual.
Resumo contido no inicio do artigo, já que a maioria não vai ler:
SEXUAL SELECTION AND HUMAN GEOGRAPHIC
VARIATION
Peter Frost.
Department of Anthropology
Université Laval
Abstract
Among early modern humans, a woman would face stronger competition for a mate the
further away she was from the equator. Men were less available because they 1) hunted
over longer distances that increased male mortality proportionately and 2) were less able
to offset the resulting man shortage through polygyny. The longer the winter, the costlier
it became to provision a second wife and her children, since women could not gather food
in winter. Women competed the most for mates in the 'continental Arctic,' where
wandering herds were the main food source. Conversely, men competed the most for
mates in the Tropics, particularly after year-round agriculture emerged. This means of
subsistence allowed women to become primary food producers, thereby freeing men to
take more wives. Because mate competition has varied in intensity among human
populations, sexual selection has correspondingly varied in intensity for certain traits,
often highly visible and colorful ones. Intense female-female competition may explain an
unusual convergence of color traits in northern and eastern Europeans. Intense male-male
competition may explain increased masculinization of body build in highly polygynous
agricultural populations of sub-Saharan Africa.