Lactose intolerance has been studied as an aid in understanding ancient diets and population movement in prehistoric societies.
Milking an animal vastly increases the calories that may be extracted from the animal, as compared to the consumption of its meat alone.
It is not surprising, then, that consuming milk products became an important part of the agricultural way of life in the Neolithic.
Roman authors recorded that the people of northern Europe, particularly Britain and Germany, drank unprocessed milk.
This corresponds very closely with modern European distributions of lactose intolerance, where the people of Britain, Germany and Scandinavia have a good tolerance, and those of southern Europe, especially Italy, have a poorer tolerance.
In east Asia, historical sources also attest that the Chinese did not consume milk, whereas the nomads that lived on the borders did. Again, this reflects modern distributions of intolerance.
China is particularly notable as a place of poor tolerance, whereas in Mongolia and the Asian steppes horse milk is drunk regularly.
This tolerance is thought to be advantageous, as the nomads do not settle down long enough to process mature cheese.
Given that their prime source of income is generated through horses, to ignore their milk as a source of calories would be greatly detrimental.
The nomads also make an alcoholic beverage, called Kumis, from horse milk, although the fermentation process reduces the amount of lactose present.
The African Fulani have a nomadic origin and their culture once completely revolved around cow, goat, and sheep herding. Dairy products were once a large source of nutrition for them.
As might be expected if lactase persistence evolved in response to dairy product consumption, they are particularly tolerant to lactose (about 77% of the population).
Many Fulani live in Guinea-Conakry, Burkina Faso, Mali, Nigeria, Niger, Cameroon, and Chad.
There is some debate on exactly where and when genetic mutation(s) occurred, although a recent study suggests that the genetic change that enabled early Europeans to drink milk without getting sick has appeared in dairying farmers who lived around 7,500 years ago in a region between the central Balkans and central Europe.
Some have argued earlier for separate mutation events in Sweden (which has one of the lowest levels of lactose intolerance in the world) and the Arabian Peninsula around 4000 BC.
However, others argue for a single mutation event in the Middle East at about 4500 BC, which then subsequently radiated. Some sources suggest a third and more recent mutation in the East African Tutsi.
Whatever the precise origin in time and place, most modern Northern Europeans and people of India, as well as people of European or Indian ancestry, show the effects of this mutation (that is, they are able to safely consume milk products all their lives), while most modern East Asians, sub-Saharan Africans and native peoples of America and the Pacific Islands do not (making them lactose intolerant as adults).
The Maasai ability to consume dairy without exhibiting symptoms may be due to a different genetic mutation, or it may be due to the fact that they curdle their milk before they consume it, removing the lactose.
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