Lactase persistence

Lactase persistence is the continued activity of the enzyme lactase in adulthood. Since lactase's primary function is the digestion of lactose in milk, in most mammal species, the activity of the enzyme is dramatically reduced after weaning. In some human populations, though, lactase persistence has recently evolved as an adaptation to the consumption of nonhuman milk and dairy products beyond infancy.

Overview

The majority of people around the globe remain lactase non-persistent throughout their life. However, not all humans become lactase non-persistent. For example, most people of European descent produce lactase throughout their life, a phenomenon known as lactase persistence. In these populations, the frequency of lactase persistence is now more than 90%, but it was less than 40% just 20,000 years ago.

Genetics

The genetic basis for lactase persistence/non-persistence is well studied. The trait is hereditary and depends on a single gene, the lactase gene (LCT). The persistence/non-persistence aspect of lactase is controlled by several polymorphisms in the MCM6 gene, located upstream of the lactase gene.

Evolution

The evolution of lactase persistence is a widely cited example of recent human evolution. It is thought to have evolved within the past 10,000 years among some populations, and the gene variant has been associated with regions where dairy animals were commonly kept.

Health implications

Lactase persistence/non-persistence can have a number of medical implications. For those who are lactase non-persistent, consumption of lactose can lead to lactose intolerance, characterized by digestive symptoms such as bloating, diarrhea, and gas. On the other hand, lactase persistent individuals have the ability to consume milk and other dairy products without these side effects.

See also

• Lactose intolerance
• Lactase
• Human genetic variation