Our moms have all warned us that we are what we eat, usually with an eye to heading us away from French fries and toward carrot sticks. Research nowadays, however, shows that what and how we eat not only affects us as individuals, but has shaped the entire human race. The birth of farming, for example, did a job on human DNA.
The Agricultural Revolution not only brought us wheat, barley, millet, peas, cows, pigs, sheep, and goats, but triggered changes in the human genome, altering everything from our digestive and immune systems to our height and skin color. Blond Scandinavian supermodels may owe their pale hair and long legs to Stone Age farming and its new approach to food, and if you can drink milk—well, thank a Neolithic farmer.
Evidence for this comes from a study by an international team of scientists, published last month in the journal Nature. The team, led by population geneticists Iain Mathieson, David Reich, and colleagues from Harvard Medical School, analyzed the genomes of 230 people from archaeological sites across Europe who lived between 2,300 and 8,000 years ago, and compared them to the genomes of modern Europeans, gleaned from the 1000 Genomes Project.
Stone Age Europe was a melting pot. Its first inhabitants came from Africa and lived as hunter-gatherers for over 35,000 years, spreading across the continent from Spain to Siberia. The next wave of people arrived about 8,500 years ago from ancient Anatolia (now Turkey) bringing with them the practice of farming. About 4,500 years ago, the farmers were followed by an influx of nomadic herders from the steppes of Russia, a population known as the Yamnaya. By comparing DNA sequences from people who lived before, during, and after the introduction of farming, the researchers were able to trace the impact of the new lifestyle on human genes. Our ancestors adapted to agriculture through a process of natural selection in which some genes triumphed and others fell by the wayside.
One of the winners was a gene called LCT that codes for lactase, the enzyme that allows adults to digest lactose, the main sugar found in milk and other dairy products. The hunter-gatherers, the first farmers, and the Yamnaya all lacked LCT and were lactose-intolerant. However, the gene swept through Europe about 4,000 years ago, most likely since it conferred such a survival advantage on people who could use milk from domesticated animals as a protein source. Neolithic farming, in other words, is why today we can enjoy milkshakes.
Another foodie gene that emerged in the wake of farming is SLC22A4, which provides instructions for a cell-surface transport protein that allows cells to more effectively absorb the amino acid ergotheoneine. Wheat and other grain crops have low levels of this nutrient; the genetic absorption boost provided needed nutritional benefits to our distant ancestors. Unfortunately, there’s a flip side to the genes that confer such digestive advantages: some variants have been linked to higher risks of celiac disease. Today, irritable bowel syndrome may be a leftover from our early adaptation to an agricultural diet.
Farming also seems to have led to a protective uptick in our immune systems. Variant immune-associated genes were a plus, since a sedentary agricultural lifestyle meant more people living close to each other and to domesticated animals, which made for an increased risk of disease.
And farming seems to have turned many of us pale.
The earliest Europeans were dark-skinned, an advantageous trait in sunny southern latitudes. The arriving Anatolian farmers, however, carried genes for light skin, and it was these genes that took off, spreading across the continent in the wake of farming and interbreeding. Hunter-gatherers from sites in Spain, Luxembourg, and Hungary from about 8,500 years ago lacked two genes—SLC24A5 and SLC45A2—that cause skin depigmentation and pale skin. On the other hand, people from a 7,700-year-old archaeological site in Sweden had both, along with a third gene, HERC2/OCA2, that gives the bearer blue eyes and may contribute to blond hair.
Pale skin in the far north is most likely driven by our need for vitamin D. At latitudes where there’s little sunlight, people don’t absorb enough ultraviolet radiation to trigger the synthesis of vitamin D by skin cells. Light skin ups UV absorption and thus is an advantage for northerners. The spread of the light-skin genes in the wake of farming, Mathieson, Reich, and colleagues suggest, may have a similar explanation: since the farmers’ diet was less heavy in meat than that of the hunter-gatherers, their vitamin D intake was reduced. Pale skin enabled wheat-eating farmers to combat vitamin deficiency.
Height, the researchers explain, is a less straightforward story, since tallness results from the interaction of many different genes. Analysis of 169 height-related genes from ancient DNA samples, however, indicated that the arriving Anatolians were on the short side, while the Yamnaya were tall. In the aftermath of the European shift to farming, Europeans—particularly in the north, which received a higher concentration of Yamnaya genes—gradually grew taller, while southerners, with a higher dose of Anatolian genes, grew shorter.
Using new DNA extraction and analytic techniques and with an increasing number of available ancient DNA samples, we may soon be able to track human evolutionary history around the world. Next may be to discover whether the genes that contribute to Type II diabetes and obesity have their roots in the Neolithic shift to farming.