Lactose intolerance is a worldwide phenomenon that has been widely studied over the years in order to understand the influences of human evolution and migration over the ages.
With the advent of farming and maintenance of livestock, drinking an animal's milk product was found to be preferable to eating just the meat of an animal. During the Neolithic Era, milk consumption became common even among adults, as agriculture flourished.
In northern Europe, particularly Britain and Germany, unprocessed milk was consumed. However, milk consumption in adults was not common in southern European countries such as Italy. Even today, lactose intolerance is seldom seen in British, German and Scandinavian populations but is commonly seen among people from southern European, especially Italians.
Similarly, in Mongolia, horse milk was consumed on a regular basis and cases of lactose intolerance are fewer compared to China where ancient civilizations did not consume milk. The African Fulani population depended on milk from their livestock and now have little or no lactose intolerance in their current populations based in locations including Guinea-Conakry, Mali, Nigeria, Chad and Cameroon, amongst others.
Studies have shown that people who consumed milk in its unprocessed form were usually nomads who did not settle down for long enough to make cheese out of the milk. Overall, these population-based and anthropological studies have shown that adult populations have adapted to milk consumption over many years.
Genetic mutations, especially in chromosome 2, seem to be at the root of this evolved lactose tolerance. Some studies have shown that a single genetic mutation occurred in around 4500 BC that spread worldwide. Another mutation could have come from the East African Tutsi population. The mutation has led to the populations of Northern Europe and India developing lactose tolerance so that they can safely consume milk and milk products. On the other hand, populations in sub-Saharan African, southern Europe and people native to America and the Pacific Islands do not continue to possess lactase into adulthood and are lactose intolerant.