Darwinian Medicine, a new interdisciplinary branch of medical science, considers why, rather than how certain conditions and symptoms develop. In the case of lactose intolerance, it has shown a clear relationship between our ancestral environment and our ability to tolerate milk sugar.

A team from Cornell University compiled data from 270 indigenous African and Eurasian populations in 39 countries, from southern Africa to northern Greenland, and found that, on average, 61% of those studied were unable to tolerate lactose, ranging from only 2% in Denmark to 100% in Zambia.

The lactose intolerance 'map' shows that it is primarily people whose ancestors came from places where dairy herds could be raised safely and economically, such as Europe, who have developed the ability to digest milk and maintain this ability throughout life. Those of Asian and African descent stop producing lactase - the enzyme required to digest milk sugar - as they mature and so lose the ability to digest milk after infancy.

The Cornell team concluded that adults from Europe can tolerate milk because their ancestors lived where dairying flourished, and passed on gene mutations which maintain lactase production into adulthood.

Source: Cornell University News Service, 1st June, 2005.

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First published in June 2005

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