A Cornell University study finds that ancestral access to dairy herds could be raised safely and economically eventually developed the ability to digest milk, such as Europe.
In the very hot or very cold climates of Africa and much of Asia, deadly cattle diseases present before 1900 prevented such practices and the populations there have not had as much time to evolve a physiological adaptation to mil digestion after infancy.
"Evolutionary biologist Paul Sherman, a professor of neurobiology and behavior at Cornell said that "This is a spectacular case of how cultural evolution - in this case, the domestication of cattle - has guided our biological evolution.""
See "Lactose Intolerance Linked To Ancestral Environment." Reported by Science Daily, 2nd June 2005.