Writing for Slate, Benjamin Phelan tackles the phenomenon known as lactose intolerance: the inability to digest milk and milk products because of a deficiency of lactase.
It seems all humans were lactose intolerant until around 10,000 B.C., when a genetic mutation appeared somewhere near modern-day Turkey that turned on the lactase-production gene permanently.
Phelan says the original mutant was probably a male who passed the gene on to his children, and those carrying the mutation could drink milk their entire lives.
“Genomic analyses have shown that within a few thousand years, at a rate that evolutionary biologists had thought impossibly rapid, this mutation spread throughout Eurasia, to Great Britain, Scandinavia, the Mediterranean, India and all points in between, stopping only at the Himalayas.”
Phelan adds that other mutations for lactose tolerance arose in Africa and the Middle East, though not in the Americas, Australia, or the Far East.
Suddenly, in evolutionary terms, 80 percent of Europeans became milk-drinkers, and in some populations, the proportion is close to 100 percent — even though globally, lactose intolerance is the norm with around two-thirds of the population unable to drink milk in adulthood.
Phelan claims the speed of this transformation remains a mystery in the story of human evolution, even more so because it’s not clear why anybody needed the mutation to begin with.
The reason is that our lactose-intolerant ancestors consumed dairy products such as yogurt without getting sick. The fermentation process that transforms milk into yogurt consumes lactose, which is a sugar.
This is why many lactose-intolerant people can eat yogurt.
Man’s hunting and gathering mode of sourcing food provided a healthy diet because of the variety, but it turned man into “a rootless species of nomads.”
Agriculture, on the other hand, offered stability.
But Phelan points out that although agriculture offered stability, once humans began to rely on the few crops that we knew how to grow reliably, our collective health collapsed.
“The remains of the first Neolithic farmers show clear signs of dramatic tooth decay, anemia, and low bone-density. Average height dropped by about 5 inches, while infant mortality rose.”
In addition to the exclusion of food variety resulting from agriculture, people began to live in cities where infectious diseases spread.
It was in these conditions that the lactose tolerance mutation took hold, says Phelan.
“Reconstructed migration patterns make it clear that the wave of lactose tolerance that washed over Eurasia was carried by later generations of farmers who were healthier than their milk-abstaining neighbors.”
Phelan adds that everywhere that agriculture and civilization went, lactose tolerance came along.
“Agriculture-plus-dairying became the backbone of Western civilization.”
The rise of civilization coincided with the human consumption of animal fluids. “Western civilization, which is twinned with agriculture, seems to have required milk to begin functioning.”
And although there are many theories, Phelan insists that it’s hard to know with any kind of certainty why milk was so beneficial.
“No one can say why.”
November 14th, 2012