A team of international scientists has just completed a comprehensive study of ancient European milk drinking habits. They wanted to see if there was a connection between increased milk consumption and the development of the capacity to digest animal milk fully and properly. It appears that a genetic mutation entering humanity’s collective genome about 4,000 years ago was responsible for the latter change. Before then humans were naturally lactose intolerant.
The Evolution of Human Lactose Intolerance
Despite the disturbing effects milk products can cause in the lactose intolerant , the scientists discovered that ancient Europeans drank milk in huge quantities for thousands of years before lactose tolerance became widespread. This is a significant finding, because it upends current evolutionary theory that suggests people only began drinking milk in large quantities after the genetic mutation that allowed them to digest it efficiently had taken root and spread through a sizeable percentage of the population.
The participants involved in this research included experts from the fields of genetics, archaeology, epidemiology, history, biochemistry, and more. They analyzed information about milk consumption in Europe from around 7000 BC to approximately 1500 AD, and discovered that patterns of consumption did not correlate with lactose tolerance to nearly the extent that had been expected.
“Prehistoric people in Europe may have started consuming milk from domesticated animals thousands of years before they evolved the gene to digest it,” the authors of this comprehensive new study explained in an article just published in the journal Nature. Since cattle were first domesticated in southwest Asia in the 9th millennium BC and introduced to Europe a few centuries after that, this statement could be 100 percent accurate.
Oxen on their way to work by Constant Troyon, 1855. The study found that prehistoric peoples began consuming milk when humans were naturally lactose intolerant. ( Public domain )
Natural Selection of a More Complex Kind
The Agricultural Revolution began about 12,000 years ago, and the domestication of dairy-producing animals like cows represented a major step forward in this transformation of humanity’s food acquisition practices. An increased tolerance for milk products followed on the heels of this dramatic change, which suggested to evolutionary scientists that there were survival-related advantages to being able to consume milk products without suffering from gastrointestinal distress.
The theory was that those who could digest milk would have gained a new source of calories and nutrients, they therefore would have been healthier and would have produced healthier children (and more of them) in comparison to those who were lactose intolerant. Lactose intolerance is the label used to designate people who lack the ability to produce the enzyme responsible for efficient milk digestion. This would have been the case whether the latter individuals chose to drink milk and suffer the consequences, or pass on milk and deal with the nutritional deficiencies that would have resulted.
In either scenario, the evolutionary scales would have been tipped toward those who could drink and digest milk completely. Those who couldn’t would have faced higher rates of premature death. Through natural selection the capacity to digest milk efficiently would have thus become more common over time—as it did starting approximately 4,000 years ago among separate populations living in Europe, Africa, South Asia, and the Middle East.
Analysis of Ancient Pottery Provides a Complicated Milk Drinking Picture
This was supposedly how human beings developed a widespread tolerance for milk after being almost universally lactose intolerant beforehand. What the new research reveals, however, is that the milk drinking picture is more complicated and interesting than previously imagined.
The scientists involved in the international study analyzed data obtained from chemical tests that found milk-fat residues on several thousand pieces of pottery collected from more than 550 archaeological sites in Europe. These pottery samples were linked to sites that had been occupied between 9,000 and 500 years ago, which allowed the scientists to determine how productive the dairy industry had been and how popular milk drinking had been at various times and in different places throughout ancient European history.
Once this exhaustive process was finished, the scientists then cross-correlated historical patterns of milk production in Europe with genetic data taken from the skeletal remains of nearly 1,300 people who’d lived in the same regions during the same 9,500-year time period, all of whom possessed the genetic markers associated with lactase persistence, lactase being the enzyme that helps the body break down and digest the sugars in milk, and persistence refers to the capacity of the body to produce ample quantities of it.
The study analyzed the molecular remains of food left in pottery discovered in Europe to assess dairy consumption throughout ancient history. In the image pottery from the archaeological site of Verson, France. (Annabelle Cocollos / Conseil départemental du Calvados )
Surprising Conclusions Emerge About the History of Lactose Intolerance
Much to their surprise, the scientists discovered that lactase persistence did not become common in Europe until around 1,000 BC. This was nearly 3,000 years after it was first detected in the ancient European gene pool, which means the genetic change that allowed for stress-free milk consumption hadn’t spread through the population as rapidly as had been previously believed.
In contrast, milk drinking had been popular for much longer. There were fluctuations in dairy production and milk drinking over the 9,500-year time period, according to the scientists’ analysis, but they did not correlate with changes in lactase persistence in any noticeable way. Interestingly, the data revealed that sudden increases in the incidence of lactase persistence were associated with periods where famines and disease outbreaks were likely experienced, independently of what was going on with the milk supply.
“All previous hypotheses for what was the ‘natural-selection advantage’ of lactase persistence pegged themselves to the extent of milk use,” study co-author Mark Thomas, an evolutionary geneticist from University College London, told Nature in a separate article from the one that introduced the results of the new research.
Obviously, the facts contradict this thesis. It seems that lactase persistence/lactose tolerance spread only in certain special conditions, specifically when societies were under siege by natural forces that threatened group survival. In these circumstances anything that improved or damaged a person’s health to even the smallest degree might have had evolutionary implications.
Milk. ( Yingko / Adobe Stock)
People Really Like Their Milk, Both Now and Then
Searching for more data to back up their findings, the scientists took a closer look at current milk consumption to see how it was impacted by lactose intolerance. Retrieving information from the UK Biobank, a collection of genetic and health-related data for 500,000 people from the United Kingdom, they found that lactose intolerance had little impact on levels of milk drinking.
Among Biobank contributors who were lactose intolerant, 92 percent preferred fresh milk over other options. Notably, the scientists also were unable to find any link between lactase persistence and better health or enhanced fertility in general.
Mark Thomas suggests the negative impact of drinking milk while lactose intolerant wouldn’t have kept people away in ancient times any more than it does now. “If you’re healthy, you get a bit of diarrhea, you get cramps, you fart a lot. It’s unpleasant, but you’re not going to die,” he said.
But effects like these could have been risky for ancient peoples who were sick from disease, infection, or malnutrition. In these circumstances, lactose intolerance could have led to higher death rates, lower fertility, and a less robust response to potentially life-threatening developments, such as drought-related crop loss, warfare, natural disasters, population growth or even more competition for resources. This would explain some of the more intriguing results of this new study, which found that ancient peoples who were exposed to pathogens and food shortages were more likely to develop widespread tolerance for milk consumption shortly thereafter.
In the final analysis, this new study did confirm that tolerance for milk products increased as a result of evolutionary pressures. Nevertheless, they concluded that this happened in response to emergency conditions and did not represent a general principle of development. Future research might very well show that other helpful genetic mutations took hold in the same way, as an indirect consequence of highly challenging environmental, social, cultural, or economic circumstances.
Top image: Farmer milking cow. Source: peopleimages.com / Adobe Stock
By Nathan Falde