About 7000 years. More like 9000 years in a few other areas of the world.
It is a weird thing to do, to drink the milk of another mammalian species. What is especially strange about it is that we can do it at all. In fact, most adult humans lack the right enzyme in their guts (lactase) to break down the primary sugar in milk (lactose). This enzyme is present in nearly all human children, but they lose it by puberty or so. But some folk, especially Europeans, some Africans and middle-easterners, can drink cow's milk all their lives; we have an advantageous mutation.
In evolutionary terms, 7000 years isn't that long. About 7000 years ago most people in Neolithic Britain couldn't drink cow's milk (analysis of DNA in bone reveals). And yet most Europeans can today.
The reason why must be that those people whose bodies continued to produce lactase into adulthood had an enormous evolutionary advantage; they were more likely to survive long enough to have children with the same late-lactase producing ability -- and thus, a certain food supply.
It is a weird thing to do, to drink the milk of another mammalian species. What is especially strange about it is that we can do it at all. In fact, most adult humans lack the right enzyme in their guts (lactase) to break down the primary sugar in milk (lactose). This enzyme is present in nearly all human children, but they lose it by puberty or so. But some folk, especially Europeans, some Africans and middle-easterners, can drink cow's milk all their lives; we have an advantageous mutation.
In evolutionary terms, 7000 years isn't that long. About 7000 years ago most people in Neolithic Britain couldn't drink cow's milk (analysis of DNA in bone reveals). And yet most Europeans can today.
The reason why must be that those people whose bodies continued to produce lactase into adulthood had an enormous evolutionary advantage; they were more likely to survive long enough to have children with the same late-lactase producing ability -- and thus, a certain food supply.