How long have adult humans been consuming milk?

Lactase is the enzyme that breaks down the milk sugar lactose, and in most mammals, including most humans, lactase activity is down-regulated after the weaning period is completed. However, in about 35% of adults worldwide, lactase continues to be expressed throughout adulthood, a feature termed lactase persistence (LP). Genetic evidence indicates that LP is a recent human adaptation, and its current geographic distribution correlates with the relative historical importance of dairying in different human populations. Investigating archaeological evidence for fresh milk consumption has proved crucial in building an account of the joint evolution of LP and dairying. A powerful technique for investigating food processing, including milk processing, in ancient populations is lipid residue analysis on archaeological pottery. We review here the archaeological and genetic evidence available that have contributed to a better understanding of the gene-culture co-evolution of LP and dairying.

Evolution of lactase persistence: an example of human niche construction

Niche construction is the process by which organisms construct important components of their local environment in ways that introduce novel selection pressures. Lactase persistence is one of the clearest examples of niche construction in humans. Lactase is the enzyme responsible for the digestion of the milk sugar lactose and its production decreases after the weaning phase in most mammals, including most humans. Some humans, however, continue to produce lactase throughout adulthood, a trait known as lactase persistence. In European populations, a single mutation (−13910*T) explains the distribution of the phenotype, whereas several mutations are associated with it in Africa and the Middle East. Current estimates for the age of lactase persistence-associated alleles bracket those for the origins of animal domestication and the culturally transmitted practice of dairying. We report new data on the distribution of −13910*T and summarize genetic studies on the diversity of lactase persistence worldwide. We review relevant archaeological data and describe three simulation studies that have shed light on the evolution of this trait in Europe. These studies illustrate how genetic and archaeological information can be integrated to bring new insights to the origins and spread of lactase persistence. Finally, we discuss possible improvements to these models.