Lactase Persistence - Evolutionary Advantages

Evolutionary Advantages

The question then arises: if lactase expression is not necessary after infancy, why has it persisted? Lactase expression persistence is largely due to natural selection. Natural selection is a component of evolution by which a trait affects the chances of the survival of organisms, and consequently, the trait becomes more prevalent in the population over time. Especially in Europe, the genetic variant -13,910*T has been strongly associated with lactase persistence and has been favored by natural selection in the past 10,000 years. Indeed, the consumption of lactose has been proven to benefit humans through adulthood. For example, the 2009 British Women's Heart and Health Study investigated the effects on women's health of the alleles that coded for lactase persistence. Where the C allele indicated lactase non-persistence and the T allele indicated lactase persistence, the study found that women that were homozygous for the C allele exhibited worse health than women with a C and a T allele and women with two T alleles. Women who were CC reported more hip and wrist fractures, more osteoporosis, and more cataracts than the other groups. They also were on average 4–6 mm shorter than the other women, as well as slightly lighter in weight. In addition, factors such as metabolic traits, socioeconomic status, lifestyle, and fertility were found to be unrelated to the findings, and thus it can be concluded that the lactase persistence benefited the health of these women.

Evidence that lactase persistence has been favored by natural selection was found in a 2006 study. The analysis process consisted of plotting extensive linkage disequilibrium of ancestral and current alleles. The researchers were able to conclude that the score did in fact reflect positive selection of lactase persistence. It has also been reported that lactase persistence presents stronger selection pressure of any other known human gene.