Re: Do we know the origin of lactose intolerance/tolerance in the human genome?

April 1, 2001 
Dear Suzanne, 
Up to about 3 years old humans can digest lactose because we have an enzyme 
called lactase. Afterwards, depending on one's alleles This process 
continues or ceases. Lactase deficiency is predominant among the world's 
people. The major hypothesis is that prior to dairy herding almost all 
humans were lactase deficient. Later on, in populations which long depended 
on dairy hearding and the ingestion of milk selection worked to the 
advantage of lactase sufficient individuals. In time, lactase suffient 
individuals increased in frequency in these populations. These populations 
include Europeans and Northeastern and Southern Africans. For further 
information see a good Physical or Biological Anthropology Textbook.
Dr. Smerken