The co-evolution of lactase persistence and dairying

 

Most Europeans take drinking milk for granted; it’s the everyday consumption of an everyday drink. But for most adult humans, indeed, for most adult mammals, milk is very far from an everyday drink. Milk is something that we have specifically evolved to be able to consume in the relatively recent past. The ability to digest the sugar in milk is called Lactase Persistence and Darwin’s engine of evolutionary change, natural selection, has probably worked harder on this trait than on any other biological characteristic of Europeans in the last 10,000 years. In this presentation we will see how Genetics, Archaeology, Anthropology, Physiology, ancient DNA and computer simulations can be combined to understand where, when and how Lactase persistence co-evolved with the culture of dairying in Europeans.

Lactase persistence (LP) is common among people of European ancestry, but with the exception of some African, Middle Eastern and southern Asian groups, is rare or absent elsewhere in the world. Lactase gene haplotype conservation around a polymorphism strongly associated with LP in Europeans (-13,910 C/T) indicates that the derived allele is recent in origin and has been subject to strong positive selection. Furthermore, ancient DNA work has shown that the -13,910*T (derived) allele was very rare or absent in early Neolithic central Europeans. It is unlikely that LP would provide a selective advantage without a supply of fresh milk, and this has led to a gene-culture co-evolutionary model where lactase persistence is only favoured in cultures practicing dairying, and dairying is more favoured in lactase persistent populations. We have developed a flexible demic computer simulation model to explore the spread of lactase persistence, dairying, other subsistence practices and unlinked genetic markers in Europe and western Asia’s geographic space. Using data on -13,910*T allele frequency and farming arrival dates across Europe, and approximate Bayesian computation to estimate parameters of interest, we infer that the -13,910*T allele first underwent selection among dairying farmers around 7,500 years ago in a region between the central Balkans and central Europe, possibly in association with the dissemination of the Neolithic Linearbandkeramik culture over Central Europe. Furthermore, our results suggest that natural selection favouring a lactase persistence allele was not higher in northern latitudes through an increased requirement for dietary vitamin D. Our results provide a coherent and spatially explicit picture of the coevolution of lactase persistence and dairying in Europe.

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