Lactase persistence is the ability of adult humans to digest lactose. This ability has its origins in different parts of the world (which occurred through convergent evolution) such as Central and Northern Europe, West Africa, the Middle East and western India.
Historically, before the development of agriculture and the domestication of animals milk was only available from the lactating mothers. Its supply stopped after the weaning period.
With a sudden change in diet from breastfeeding through weaning, specifically because of the absence of milk, lactase was not required anymore and so its production by the body was drastically reduced.
Around 8000 years ago, Europe started domesticating milk-producing animals, allowing the consumption of milk on a regular basis. The trend spread to the Middle East and West India. (3)
In Africa, especially in the countries south of the Sahara, lactose persistence most likely originated thanks to the domestication of the camel. (4)
Consistent milk consumption existed in these locations for about 8,000 years which allowed for the genetic mutation to occur resulting in lactase persistence.
To visualize the centers of lactose persistence or see where lactose intolerance is most prevalent, see the following map. Red color represents the most lactose tolerant populations, while blue represents a high percentage of lactose intolerance. The further from the centers, the more lactose intolerant the populations are. (5)