Lactase persistence (LP) is a genetically determined trait whereby the enzyme lactase is expressed throughout adult life. Lactase is necessary for the digestion of lactose – the main carbohydrate in milk – and its production is down-regulated after the weaning period in most humans and all other mammals studied. Several sources of evidence indicate that LP has evolved independently, in different parts of the world over the last 10,000 years, and has been subject to strong natural selection in dairying populations. In Europeans LP is strongly associated with, and probably caused by, a single C to T mutation 13,910bp upstream of the lactase (LCT) gene (-13,910*T). Despite a considerable body of research, the reasons why LP should provide such a strong selective advantage remains poorly understood. In this study we examine one of the most widely cited hypotheses for selection on LP – that fresh milk consumption supplements the poor vitamin D and calcium status of northern Europe’s early farmers (the calcium assimilation hypothesis). We do this by testing for natural selection on -13,910*T using ancient DNA data from the skeletal remains of eight late Neolithic Iberian individuals, whom we would not expect to have poor vitamin D and calcium status because of relatively high incident UVB-light levels. None of the 8 samples successfully typed in the study had the derived T-allele. In addition, we reanalyse published data from French Neolithic remains to both test for population continuity and further examine the evolution of LP in the region. Using simulations that accommodate genetic drift, natural selection, uncertainty in calibrated radiocarbon dates, and sampling error, we find that natural selection is still required to explain the observed increase in allele frequency. We conclude that the calcium assimilation hypothesis is insufficient to explain the spread of lactase persistence in Europe.
It thus seems likely that population turnover since or shortly after the Neolithic transition has been less severe in southwestern Europe than in central or northern Europe.
Correction: I wrongly reported the main European lactase persistence SNP as rs13910*T, when it is in fact rs4988235(T)
(already corrected in the text above) This was caused by the
nomenclature used in the Sverrisdóttir paper, where it refers to it as
-13910*T, which must be some other sort of naming convention. Thanks to Can for noticing.
- And in general category: lactose intolerance