Bonus – Lactose tolerance
Another story of evolution…
Man has been drinking milk for some 9,000 years, even though he has long been lactose intolerant as an adult.
Lactose is the main sugar found in milk. Lactose intolerance is a normal physiological phenomenon. It is caused by a decrease in the production of an enzyme called lactase (LCT) in early adulthood. This lactase is present in the small intestine (more information on the lactase in the UniProtKB database).
The persistence of lactase in adulthood is the consequence of genetic variations in the MCM6 gene, variations that appeared in the human population long after the start of milk consumption.
In some 6,000 years, these genetic variations have spread like wildfire in Europe. One hypothesis is that diseases and famines in those periods favored the emergence of these genetic variations, lactose intolerance being possibly fatal under these extreme conditions.
Today, nearly 1/3 of the world’s population is tolerant to lactose in adulthood.
