how come a lot of people are lactose intolerant if everyone started off by drinking milk as a baby?

Question

how come a lot of people are lactose intolerant if everyone started off by drinking milk as a baby?

In: 327

Answer 1

Most of the world is lactose intolerant. The ones that aren’t have lactose persistence. Everyone can digest lactose as a baby, but those with persistence never lose the ability as they grow up. It is a trait that evolved in regions where people drink a lot of dairy, like Scandinavia. In places without milk drinking, producing the enzyme to digest milk as an adult is wasted metabolic effort.