for National Geographic News
Milk wasn't on the Stone Age menu, says a new study which suggests the vast majority of adult Europeans were lactose intolerant as recently as 7,000 years ago.
While cow's milk is a mainstay in the diet of modern-day Europeans, their ancestors weren't able to digest the nutritious dairy product after childhood, according to DNA analysis of human skeletons from the Neolithic period.
The study was led by Joachim Burger of the Institute of Archaeology at Mainz University in Germany.
The findings supports the idea that milk drinkers became widespread in Europe only after dairy farming had become established there—not the other way around.
Most mammals lose their ability to digest milk after being weaned, but some humans can continue to benefit from the calcium-rich, high-energy liquid.
This is because they carry a mutation that lets them continue producing lactase, the gut enzyme needed to break down the milk sugar lactose, in adulthood.
Lactose tolerance is most common in people of European origin, especially those from the northern and central areas of the continent. It is relatively rare in Asian and Native American populations.
High levels of lactose tolerance among these European groups are thought to reflect an evolutionary advantage. Early farming communities that could digest milk could consume the liquid during otherwise poor harvests, for instance.
Some scientists argue this adaptation was previously very rare in humans, spreading only after the introduction of farming to Europe.
Others say prehistoric populations were already split between those who could and couldn't drink milk as adults. This split, the researchers say, determined which groups became dairy farmers.
Burger's team analysed the DNA of well-preserved Stone Age skeletons from locations in northern and central Europe.
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