Pedigree information from families provide support for this explanation. The following three sample pedigrees of American Indian families illustrates this concept. About 10,000 years have passed since the milking of domestic animals was begun. Nigeria is a case that demonstrates the significance of this lifestyle on human evolution. In the southern region, where conditions are not favorable for cattle, milk is not part of the diet.
People there develop lactose intolerance.
In contrast, a nomadic tribe that has been raising milk cattle for thousands of years remain lactose tolerant. Most African Americans are descendants of the nonpastoral tribes from Western Africa and do not tolerate lactose well. This has strong implications in relief efforts to aid those suffering from starvation in various parts of the world. Powdered milk has been a favorite food for shipping to needed areas but it frequently causes illness in those people the aid is meant to help. Calcium deficiency can be a dietary concern for seven out of ten African Americans who are lactose intolerant and who should avoid eating large quantities of dairy products.