Lactase persistence

Lactase persistence is the continued activity of the enzyme lactase in adulthood. Since lactase's only 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. The majority of people around the world remain lactase nonpersistent, and consequently are affected by varying degrees of lactose intolerance as adults. However, not all genetically lactase nonpersistent individuals are noticeably lactose intolerant, and not all lactose-intolerant individuals have the lactase nonpersistence allele.