http://en.wikipedia.org/wiki/Lactose_intoleranceQUOTE
Lactose intolerance is the inability to metabolize lactose, a sugar found in milk and other dairy products, because the required enzyme lactase is absent or its availability is lowered. It is estimated that 70% of adult humans are lactose intolerant.
* 6% to 15% in white Americans and northern Europeans
* 18%, 30%, and 47% in Mexican Americans
* 25%, 45%, and 60% in black South Africans
* approximately 30%, 80%, and 85% in Chinese and Japanese
* 30–55%, 90%, and >90% in Mestizos of Peru[26][27]
Most of us lose our ability to digest the lactose sugar by 4 years old. Some peoples retain theirs, like the Masai of Africa, Most Europeans, half of Hispanic peoples, and only 20-10% of Asian population retain that enzyme lactase.
Almost 100% of Native Americans are lactose intolerant.