Impact of Selection and Demography on the Diffusion of Lactase Persistence – PLoS ONE

Here’s a freely accessible paper which amongst many considerations, discusses genetic diffusion in pastoral human populations at the Neolithic transition, and why Lactose Persistence, or specifically lactase persistence allele(s) (LCT*P),  which allows for the digestion of fresh milk, was strongly selected for in northern Europe, at the start of agricultural domestication. This is the introduction:

Lactase is an enzyme that allows lactose digestion in fresh milk. Its activity strongly decreases after the weaning phase in most humans. However, in many European individuals and in people from various populations of other continents, lactase is still active throughout adult life [1]. This dominantly inherited genetic trait is called lactase persistence and at least three mutations are tightly associated with it: −13,910 C/T (generally linked to −22,018 G/A) in northern Europe (100% association) [2], [3], −14,010 G/C in East Africa and −13,915 T/G in the Middle-East/North Africa [4], [5]. In this study, we will use LP to refer to the lactase persistence phenotype, LCT to refer to the lactase gene and LCT*P to refer to the lactase persistence associated allele(s).

The particular distribution of lactase persistence throughout the world indicates that this trait evolved under strong positive selection [5], [6], [7]. Two main hypotheses have been proposed: gene-culture coevolution (gcc) [8], [9], which suggests that lactose digestion confers a nutritional advantage to milk-consuming (e.g. pastoralist) populations; and calcium assimilation (cal) [10], which proposes that carriers of LCT*P are favoured in high-latitude regions, where lactose would substitute vitamin-D (deficient when sunlight is low) to allow accurate calcium assimilation, thus preventing rickets. Holden and Mace [11] studied the two mentioned hypotheses and a third one, proposing that LP was favoured in highly arid environments, where people would have drunk milk to prevent dehydration [12], [13]. Their conclusion was that LP is an adaptation to pastoralism, in agreement with the gcc model, while no evidence for the other hypotheses was found. Compatible with this theory, Coelho et al. [14] suggested that −13,910*T originated in Eurasia before the Neolithic Era, and observed a significant departure from neutrality of this variant in the few populations examined. On the other hand, these studies do not explain the significant correlation found between LP frequencies and latitude in Europe [15], as predicted by the cal model.

Reference: Selection and Demography on the Diffusion of Lactase Persistence

Gerbault P, Moret C, Currat M, Sanchez-Mazas A, 2009 Impact of Selection and Demography on the Diffusion of Lactase Persistence. PLoS ONE 4(7): e6369. doi:10.1371/journal.pone.0006369

See also: Science DailyLonger Life For Milk Drinkers, Study Suggests

4 thoughts on “Impact of Selection and Demography on the Diffusion of Lactase Persistence – PLoS ONE

  1. Interesting. I miss the sampling of Basques, who have the highest lactase persistence levels in Southern Europe (very close to those found in the North in fact).

    Several factors are speculative. There is some (necessarily scant) evidence that Neolithic Central Europeans did not have the LPT gene but we know nothing of Atlantic Neolithics, among whom this trait is most common nowadays. This is important, I’d say, because the trait shows significant correlation with neutral genes, like Rh, what makes me think it was actually present in relative high levels among pre-Neolithic Europeans (why? accident maybe – otherwise I’d have to start speculating again about Magdalenian horse domestication).

    Whatever the case the authors seem to have confirmed some selection in NW Europe for this trait (but looks neutral in the rest).

  2. pretty interesting archaeogenetics. has anyone studied whether vitamin d production differences in the northernmost regions of europe versus the southernmost regions is so vastly different that rickets is more of a problem in say, scandinavia compared to northern spain?

  3. Vitamin D is much more than mere rickets. Vitamin D is essential for correct brain development in embryos and children, for good bactericidal response and even prevents artherosclerosis.

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