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ABSTRACT The main carbohydrate in milk is lactose, which must be hydrolyzed to glucose and galactose before the sugars can be digested. While 65% or more of the total human population are lactose intolerant, in some human populations lactase activity commonly persists into adulthood. Lactose tolerance is exceptionally widespread in Northern European countries such as Sweden and Finland, with tolerance levels of 74% and 82%, respectively.Theoretically, this may result either from a strong local selection pressure for lactose tolerance, or from immigration of lactose tolerant people to Northern Europe. We provide several lines of archaeological and historical evidence suggesting that the high lactose tolerance in North Europeans cannot be explained by selection from in situ milk consumption. First, fresh cow milk has not belonged to the traditional diet of Swedes or Finns until recent times. Second, not enough milk has been available for adult consumption. Cattle herding has been neither widespread nor productive enough in Northern Europe to have provided constant access to fresh milk. We suggest that the high prevalence of lactose tolerance in Finland in particular may be explained by immigration of people representing so-called Corded Ware Culture, an early culture representing agricultural development in Europe.
THE MAIN CARBOHYDRATE in milk is a sugar called lactose, which must be broken down (hydrolyzed) to the monosaccharides glucose and galactose by the enzyme lactase (or lactase-phlorizin hydrolase) before the sugars can be digested by the human intestine. If there is no lactase enzyme activity in the villi of enterocytes of the small intestine, bacterial procession of lactose causes diarrhea, bloating, and flatulence (Järvelä et al. 2009). Moreover, the absorption of other nutrients such as calcium may become disturbed in the absence of lactase.
In adult mammals, lactose tolerance or lactase persistence (LP) normally disappears after weaning.However, in some human populations lactase activity persists into adulthood. According to Ingram et al. (2009), lactase non-persistence phenotype is frequent in humans, affecting an estimated 65% or even more of the total human population (Campbell,Wand, and Matthews 2005). Geographical variation in the degree of lactase persistence is remarkable (Swallow 2003). LP remains common in adult inhabitants of Northern Europe, or more generally those of Northern European ancestry, as well as in some pastoralist populations from Africa and the...