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Lactase persistence is a textbook example of natural selection in humans: it has been reported to present stronger selection pressure than any other known human gene. [24] However, the specific reasons as to why lactase persistence confers a selective advantage "remain open to speculation". [41]
Both mutations, C→T at position -13910 and G→ A at position -22018, have been independently linked to lactase persistence. [27] The lactase promoter is 150 base pairs long and is located upstream of the site of transcription initiation. [27]
Lactase persistence is a rare ability among mammals. [74] Because it involves a single gene, it is a simple example of convergent evolution in humans. Other examples of convergent evolution, such as the light skin of Europeans and East Asians or the various means of resistance to malaria, are much more complicated. [16]
Many adults are lactose intolerant because their bodies cease production of the enzyme lactase post childhood. However, mutations in the promoter region of the lactase gene (LCT) result in the continued production of lactase throughout adulthood in certain African populations, a condition known as lactase persistence. A study conducted by Sarah ...
Lactase persistence One of the best known examples is the prevalence of the genotype for adult lactose absorption in human populations, such as Northern Europeans and some African societies, with a long history of raising cattle for milk.
In most mammals, production of lactase diminishes after infants are weaned from maternal milk. However, 5% to 90% of the human population possess an advantageous autosomal mutation in which lactase production persists after infancy. The geographic distribution of lactase persistence is concordant with areas of high milk intake.
Mendelian traits behave according to the model of monogenic or simple gene inheritance in which one gene corresponds to one trait. Discrete traits (as opposed to continuously varying traits such as height) with simple Mendelian inheritance patterns are relatively rare in nature, and many of the clearest examples in humans cause disorders.
Genetic evidence shows that lactase persistence developed in East African populations between 7000 BP and 3000 BP, which is consistent with existing evidence for the introduction of livestock. [15] The shift from hunting-gathering to herding developed gradually, over thousands of years, during the Pastoral Neolithic. [15]