It is my understanding, that humans that are descended from indigenous populations whose society was built around herding animals for milk and meat are actually very well adapted to consuming milk. This was important for survival during winter periods, when milk and meat were the primary foods available.

Populations that over centuries adapted to a more agrarian society are not adapted to drinking milk and tend to suffer lactose intolerance. Instead, their diets are more geared to fish, limited amounts of meat, grains and vegetables.

The same can be said of "gluten". Agrarian societies where wheat and other high gluten grains were consumed, tend to have lower rates of gluten intolerance, while those societies that did not rely on high gluten grains are more prone to gluten intolerance.

There is a tendency to say all humans are the same... but the truth is we are fundamentally the same, but we also have very stark differences in how our bodies respond to the environment including the foods we eat based on where we came from.