The geographic hypothesis and lactose malabsorption. A weighing of the evidence.

Reviewed in this article is evidence bearing on the geographic hypothesis advanced eight years ago to explain the striking ethnic or racial differences in prevalence of primary adult lactose malabsorption that are found around the world. Most evidence is found to support the hypothesis and the likelihood that some human groups came to have low prevalences of such lactose malabsorption because of selective pressures over a long historical period that favored the adult lactose absorber under particular ecological conditions.