Ancient DNA uncovers the origins of our ability to digest milk
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SYDNEY: A new genetic analysis of ancient human remains proves that humans were unable to digest milk prior to the spread of agriculture and dairy farming within the last 8,000 years.
Though all people can digest milk in infanthood, most of the world's population lose that ability at between two and five years of age.
At this time their bodies stop producing an enzyme called lactase, which is essential for digestion of lactose sugars found in dairy products. Most Asians, sub-Saharan Africans, native Americans and Pacific Islanders remain lactose intolerant today.
However, a mutation in many European and some African populations allows them to produce lactase into adulthood, and in these cultures dairy products - such as milk cheese and yoghurt - traditionally form a key component of the diet.
Researchers had been unable to agree on whether the ability to digest milk spread along with the practice of dairy farming or, conversely, whether dairy farming spread only in those populations that already had the mutation.
Now, researchers at Mainz University in Germany and University College London in England have settled the debate by extracting DNA sequences from the skeletons of nine Neolithic humans. These people come from sites across Europe and all lived around 8,000 years ago. The researchers found that the version of a gene, which allows Europeans to produce lactase today, was not present in these ancient people.
The absence of this gene, "indicates that the early farmers of Europe were not yet adapted to the consumption of unprocessed milk," write the authors this week in the U.S. journal Proceedings of the National Academy of Sciences.
This is some of the best "direct evidence that natural selection is working on human populations" lead author Joachim Burger told Cosmos Online. "It shows that a genotype that is nearly absent 8,000 years ago, can rise to a frequency of more than 70 per cent today, by natural selection."
The study adds to evidence that modern central and northern Europeans are mostly the descendents of a small group of dairy farmers found in the 5th millennium BC, he said.
"The ability to drink milk is the most advantageous trait that's evolved in Europeans in the recent past. Without the enzyme lactase, drinking milk in adulthood causes bloating and diarrhoea," said co-author Mark Thomas.
"The benefits of milk tolerance … include: the continuous supply of milk compared to the boom and bust of seasonal crops, its nourishing qualities and the fact that it's uncontaminated by parasites - unlike stream water - making it a safer drink. All in all, the ability to drink milk gave some early Europeans a big survival advantage," said Thomas
Geneticist Walter Bodmer at the University of Oxford in England, commends the painstaking four years of work that went into ensuring the DNA samples were free from contamination - a common problem when extracting DNA from ancient remains. "This study confirms that lactose tolerance was rapidly selected for after the development of agriculture," he said.
More information:
Joachim burger, Mainz University
Lactose intolerance, Wikipedia
Proceedings of the National Academy of Sciences
Lactose intolerant
We may have been lactose intolerant, but it doesn't mean we didn't drink milk.
Raw milk has an enzyme in it, called Lactase. So perhaps it is not that they didn't drink milk, but that they did not drink processed milk.
If you think about it, many African Americans are lactose intolerant, but in the African continent the Dinka, Neur and a majority of tall African tribes practically live on milk as their staple food.