Gene–culture coevolution: lactase persistence

Abstract

Our capacity for culture, or for social learning, is one of the defining characteristics of our species and is responsible for our extraordinary demographic success. Cultural practices play a large role in shaping the human environment and therefore in shaping our ongoing evolution. The concept that species shape the environment in which they evolve is known as niche construction. Conversely, the genetic makeup of human populations may influence the cultural ideas and practices they adopt. In other words, genes and cultures coevolve. Lactase persistence, the ability to digest lactose and therefore to drink fresh milk after the nursing period, exemplifies the process of gene-culture coevolution. Most people have the phenotype of lactase restriction. The expression of lactase (the enzyme required for the digestion of lactose) and the ability to drink fresh milk is restricted to the nursing period and declines in mid-childhood, shortly after weaning. Older children and adults have lactose intolerance and are unable to consume fresh milk. Many people in populations that have a long history of dairying have the trait of lactase persistence. They express lactase and can consume fresh milk throughout life. Clearly, the availability of fresh animal milk created an environment that selected for lactase persistence. Likewise, the cultural practices of dairying and milk drinking have spread in populations with a high prevalence of people with lactase persistence.