In "Direct evidence for positive selection of skin, hair, and eye pigmentation in Europeans during the last 5,000 y" Wilde et al. suggest that, in addition to low sunlight exposure, a transition to farming exerted a selection pressure in favor of less skin melanin in the evolution of Europeans:
This hypothesis may explain why Northern populations that did not transition to farming – such as Mongolians, Eskimos, and the Eurasian tribes that populated North America – have retained darker skin until present times, while Europeans became white.
This could mean that white Europeans are descendants of ancestors specifically adapted to a more plant-based agricultural diet providing less dietary vitamin D than a hunter-fisher-gatherer diet would provide.
This evidence-based hypothesis suggests that modern white Europeans may be more highly genetically adapted to a farmed, highly plant-based diet than to an animal-based hunter-fisher-gatherer diet. It casts additional doubt on the paleolithic diet hypothesis that modern people, particularly modern white Europeans, should avoid farmed foods such as whole grains and legumes, and stick to the diet eaten by (dark-skinned) hunter-gatherers 50,000 years ago.