The mutation for milk-drinking evolved independently in different parts of the world over the last 10,000 years as a result of strong natural selection, but why was it so advantageous?
Among the more momentous developments in human evolution was the ability to digest milk beyond early childhood.
Mutations that enabled lifelong milk drinking appeared independently in several parts of the world over the last 7,500 years, according to growing evidence. And those genes spread rapidly. Today, about a third of adults around the world can drink milk without stomach problems, a trait known as lactase persistence.
But why was milk drinking so advantageous to humankind?
A new study debunks one leading theory: that milk provided a valuable source of vitamin D, which would've helped people absorb its calcium.
Newly analyzed human skeletons from an ancient site in Spain show that the milk-drinking gene spread just as rapidly in that sun-drenched climate as it did in other places, suggesting that milk must have been beneficial there for some reason other than its vitamin D content.