Lactose Tolerance: The Genetic Mystery Behind Milk Drinking

Abstract

Lactose tolerance, or the ability to digest lactose into adulthood, is one of the most prominent examples of recent human genetic evolution. In contrast to most other mammals, in which the activity of the lactase enzyme decreases post-weaning, some human populations have evolved lactase persistence, allowing for the lifelong consumption of milk and dairy products. The purpose of this study is to explore the genetic, evolutionary, and population dynamics behind lactose tolerance. This review integrates evidence from genome-wide association studies (GWAS), population genetics, and anthropology to examine the worldwide distribution of lactase persistence alleles. The results show a significant link between lactase persistence and past dairy cattle-keeping cultures, providing evidence for a gene-culture co-evolutionary model. Lactase persistence is believed to have evolved in Europe during the Neolithic transition, together with the domestication of animals and the development of agriculture. Independent adaptations also occurred in African and Middle Eastern pastoralist groups. Some important regulatory single-nucleotide polymorphisms (SNPs) that play a crucial role in the persistence of lactase expression in adulthood are found upstream of the LCT gene, especially −13910T and −14010C. The distribution of these variants differs considerably among different populations, which is a result of different evolutionary pressures driven by dietary selection. Besides genetic factors, epigenetics and gene-environment interactions could also affect lactase activity. In conclusion, this study illustrates the intricate dynamics among genetic transmission, dietary practices, and natural selection in the evolution of human nutritional adaptation. The evolutionary origins of lactose tolerance provide important information on human population diversity, evolution, and contemporary health aspects of lactose intolerance.