Milk drinking: in our genes?

The ability to digest the milk sugar lactose ? also known as lactase persistence ? is a selectively advantageous and recent evolutionary genetic trait, which emerged about 7,500 years ago in Europe and probably later in other parts of the world. This means that, once weaned, people in most parts of the world (large parts of Africa, most of Asia, and Oceania) cannot digest milk for the rest of their life. However, the study published in BMC Evolutionary Biology, shows that the four genetic mutations currently associated with the ability to digest milk cannot explain why many people in western and southern Africa, south eastern Europe, the Middle East, and southern and central Asia are able to digest milk. It also suggests that other genetic variants leading to the ability to digest milk exist, but have not yet been discovered. Lactase is the enzyme that breaks the lactose into two units that are digestible. It is produced by a gene and is active in human (and most mammalian) infants. Most human (and mammalian) adults cannot digest the sugar milk lactose after weaning.