For many adults in the world, the phrase “got milk?” is quickly followed by “got a nearby toilet?” Lactose, the primary sugar in milk, is a universal favorite in infancy but into adulthood the level of lactase-phlorizin hydrolase, the enzyme that metabolizes lactose in the small intestine, decreases and digestion of dairy products becomes difficult. In some populations, however, such as those located in northern Europe, the ability to digest milk remains most likely as a result of lifestyles based around cattle domestication. In 2002 Finnish scientists localized the genetic mutation that conferred this trait in northern Europeans to two regions on chromosome 2.
Now, the results of a four-year, international research project find that communities in East Africa leading traditionally similar pastoral lives evolved their ability to drink milk rapidly and independently of the northern Europeans. According to University of Maryland biologist Sarah Tishkoff, the lead author of a study appearing in today’s Nature Genetics, the mutation allowing them to “get milk” arose so quickly and was so advantageous that “it is basically the strongest signal of selection ever observed in any genome, in any study, in any population in the world.”
Swallow concedes: ” It looks jolly well as though drinking milk as an adult was good for some of us at some time in our history, that’s for sure.” African Adaptation to Digesting Milk Is “Strongest Signal of Selection Ever”
Lactose: some of us tolerate it, some of us don’t. Lactose intolerance is far more common than people think. Digestive problems associated with milk in an adult are more likely to be lactose intolerance than milk protein allergies or intolerances.
Digestive problems associated with breast milk in babies, on the other hand, are more likely to be caused by food chemicals than lactose intolerance.