Your ancestors didn’t.
About 10 millennia ago, human adults couldn’t drink milk.
The BBC article, “How Human Culture Influences Our Genetics,” outlines why the human adults of today are more lactose tolerant, while those of yesteryear were not.
Lactose tolerance – or intolerance – is genetic.
Prior to dairy farming, only children could manage to chug a glass of milk without getting sick.
When some cultures began dairy farming, a genetic mutation created an ability amongst adults to digest milk properly.
This mutation was passed on to offspring over time.
Last week, we discussed how culture is outpacing genetics when it comes to human evolution.
This is one example where culture may not have outpaced genetics but still worked symbiotically to evolve a tolerance to milk through natural selection.
Lactose Tolerance Today
As mentioned, those cultures with a background in dairy farming are significantly more lactose tolerant today, because they’ve developed the related gene.
This is another example of how culture impacts biological evolution.
That gene effectively produces the enzyme, lactase, which breaks down lactose (the sugar found in dairy products) in the small intestine.
Cultures with a higher prevalence of lactose intolerance see lesser production of lactase in infancy.
Upwards of 70 percent of adults from East Asian and West African cultures suffer lactose intolerance, along with those of Greek, Italian, Jewish, and Arab heritage.
On the opposite end of the spectrum, those cultures with high lactose tolerance include Northern European cultures, particularly those of the Nordic region.
The populations of Sweden and Finland have a reported tolerance of 74 percent and 82 percent, respectively.
These tolerance levels might be related to the immigration of lactose tolerant groups to these regions, rather than a background in dairy farming, as the cultures aren’t historically rooted in the production or consumption of milk.
But these countries may be the exception that proves the rule.
As anthropologist and co-author of The 10,000-Year Explosion: How Civilization Accelerated Human Evolution, Henry Harpending, writes:
“Which came first, the cattle or the mutation, you can’t tell. If the mutation had not occurred, there wouldn’t be so much dairying. But if people who could digest lactose didn’t have cattle, the mutation would have had no advantage.”
The Cow or the Milk
Although we may not know what came first – the cow or the milk tolerance – we can spot some aspects of “survival of the fittest” in the evolution of these cultures.
Cultures with higher lactose tolerance were historically able to survive famine at a higher rate and may have even made for stronger warriors, due to bone health.
In his research on the subject, Professor Daniel Wegmann of the University of Fribourg in Switzerland, concludes:
“Over the past 3,000 years, lactase-persistent individuals had more children or, alternatively, those children had better chances of survival than those without this trait.”
We can only expect lactose tolerance to grow even more within the next 3,000 years.