The Origins of Lactase Persistence in Europe

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. Modern DNA evidence indicates that this trait: (1) is caused, in Europeans, by a single mutation that arose in the last 12,000 years (-13,910*T), (2) has evolved independently multiple times in Africa, and (3) has been the target of strong natural selection. Furthermore, ancient DNA work has shown that the -13,910*T variant 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 lead 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 variant frequency and farming arrival dates across Europe, and approximate Bayesian computation to estimate parameters of interest, we infer that the -13,910*T variant 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. Furthermore, our results suggest that natural selection favouring a lactase persistence variant 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 co-evolution of lactase persistence and dairying in Europe.