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article imageAbility to digest milk is linked to a history of cattle rearing

By Tim Sandle     Mar 20, 2014 in Environment
A new study into lactose tolerance investigated the genetic origins of this ability. The findings reveal that the ability to digest milk was a powerful selective force in a variety of populations which raised cattle and consumed the animals' fresh milk.
Most babies are born with the ability to digest lactose, the sugar found in milk. However, some are not. The condition is known as lactose intolerance. This is the inability to digest lactose, a sugar found in milk and to a lesser extent dairy products. As a genetic disorder, it prevents babies from drinking human milk, which nearly quarters its risk of Sudden Infant Death Syndrome.
Most humans lose this ability after infancy because of declining levels of the lactose-digesting enzyme lactase. Some people can maintain high levels of lactase, and so arguably they reap the nutritive benefits of milk.
Research has shown that northern Europeans and people with northern European ancestry, as well as populations from Africa, the Arabian Peninsula and Central Asia with a tradition of fresh milk production and consumption, continue to express the lactase enzyme into adulthood. This relates to mutation that regulates the expression of the gene that codes for lactase.
To look at these further, researchers led field studies to often-remote areas of Kenya, Tanzania and Sudan to collect blood samples and perform a lactose tolerance test on people from diverse ethnic backgrounds. To look for genetic variations among the populations' abilities to digest milk, the researchers undertook genetic testing.
The analysis showed strong evidence of recent positive selection affecting several variants associated with lactase persistence in African populations. This is likely to have been a response to the cultural development of pastoralism.
The study was carried out by the University of Pennsylvania. The findings have been published in the American Journal of Human Genetics, in a paper titled “Genetic Origins of Lactase Persistence and the Spread of Pastoralism in Africa.”
More about Milk, lactose intolerant, lactose, Cows, Africa
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