Abstract
Ruminant milk and dairy products are important food resources in many European, African, and Middle Eastern societies. These regions are also associated with derived genetic variants for lactase persistence. In mammals, lactase, the enzyme that hydrolyzes the milk sugar lactose, is normally down-regulated after weaning, but at least five human populations around the world have independently evolved mutations regulating the expression of the lactase-phlorizin-hydrolase gene. These mutations result in a dominant lactase persistence phenotype and continued lactase tolerance in adulthood. A single nucleotide polymorphism (SNP) at C/T-13910 is responsible for most lactase persistence in European populations, but when and where the T-13910 polymorphism originated and the evolutionary processes by which it rose to high frequency in Europe have been the subject of strong debate. A history of dairying is presumed to be a prerequisite, but archaeological evidence is lacking. In this study, DNA was extracted from the dentine of 36 individuals excavated at a medieval cemetery in Dalheim, Germany. Eighteen individuals were successfully genotyped for the C/T-13910 SNP by molecular cloning and sequencing, of which 13 (72%) exhibited a European lactase persistence genotype: 44% CT, 28% TT. Previous ancient DNA-based studies found that lactase persistence genotypes fall below detection levels in most regions of Neolithic Europe. Our research shows that by AD 1200, lactase persistence frequency had risen to over 70% in this community in western Central Europe. Given that lactase persistence genotype frequency in present-day Germany and Austria is estimated at 71–80%, our results suggest that genetic lactase persistence likely reached modern levels before the historic population declines associated with the Black Death, thus excluding plague-associated evolutionary forces in the rise of lactase persistence in this region. This new evidence sheds light on the dynamic evolutionary history of the European lactase persistence trait and its global cultural implications.
Highlights
Lactase persistence (LP) is a common genetic trait in many European, African and Middle Eastern populations
We demonstrate that the frequency of the LP in this western Central European community, had already reached modern levels by AD 1200, and we report the highest LP T-13910 allele frequency determined to date for any ancient population
Non-European LP single nucleotide polymorphism (SNP) were not identified within our samples
Summary
Lactase persistence (LP) is a common genetic trait in many European, African and Middle Eastern populations. The enzyme lactase hydrolyses the milk disaccharide lactose into its component monosaccharides, galactose and glucose for absorption in the small intestine. If it is absent, the lactose cannot be absorbed by the intestinal mucosa and reaches the colon undigested where it is fermented by colonic bacteria, often causing symptoms such as abdominal pain, bloating and diarrhea [5]. Modern frequencies of lactase persistence vary throughout Europe according to a geographic cline. They are highest in northwestern Europe, gradually declining towards the southeast [6]. Because milk is the only natural source of lactose, it is thought that a culture of dairying must correlate with lactase persistence to some extent
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