Some 4,000 years ago, as the Minoans flourished on Crete and the Neo-Sumerians held sway in Mesopotamia, a quieter transformation unfolded in the DNA of people living across Europe and the Near East. A study published last week in Nature reveals that two genetic variants linked to celiac disease became markedly more common during this period — a shift driven not by migration or cultural change, but by natural selection acting directly on human biology.
The research, led by scientists at Harvard University, analyzed the genomes of 22,000 individuals: 10,000 ancient genomes never before studied, 6,000 previously published ancient sequences, and 6,000 modern genomes for comparison. Spanning regions from Iceland to Israel and from Spain to Iran, the dataset allowed researchers to track how gene frequencies changed over the past 10,000 years. What they found was a pattern of pervasive directional selection — meaning certain gene variants consistently increased in frequency as they conferred a survival or reproductive advantage.
Before this study, only 21 such genetic shifts attributable to natural selection — as opposed to demographic events like population movements or admixture — had been documented in humans. This work identified hundreds more, with the celiac-linked variants standing out for their dramatic rise in frequency. One of these variants, associated with immune response to gluten, became significantly more common in populations that had adopted agriculture and were consuming more cereals.
“It’s so powerful to be able to watch evolution happening in action, not just to study the scars that evolution leaves on modern patterns of variation,” said David Reich, the study’s senior author and a geneticist at Harvard, in a video interview with The Times of Israel. Reich, whose lab has pioneered methods for extracting and analyzing ancient DNA, noted that the technology to retrieve usable genetic material from ancient human remains only became available around 2010. Since then, the field has transformed our understanding of the past, allowing researchers to observe evolutionary processes in real time across millennia.
The study’s approach differed from earlier ancient DNA research, which often focused on tracing migrations or reconstructing population histories. Instead, the team treated ancient genomes as a window into biological adaptation — asking how traits like disease susceptibility, metabolism, or immune function changed under evolutionary pressure. This shift in perspective reflects a broader maturation of the field: early pioneers in ancient DNA were often archaeologists or historians; today, many are biologists and geneticists interested in the mechanics of human evolution.
One of the study’s deeper implications lies in its challenge to the idea that genetic adaptations to pathogens or dietary changes are rare or fleeting. The celiac-associated variants, while increasing susceptibility to an autoimmune disorder in modern environments, may have offered advantages in the past — perhaps by enhancing immune defense against intestinal pathogens common in dense, agricultural settlements. This trade-off, where a gene variant increases risk for a condition today but was beneficial yesterday, illustrates how evolution does not optimize for health in the modern sense, but for reproductive success in a given ecological context.
The research also underscores the role of agriculture as a driver of biological change. As farming spread across West Eurasia over the last 10,000 years, human diets shifted dramatically toward domesticated cereals like wheat and barley. The rise in celiac-linked variants suggests that populations adapting to this new dietary landscape underwent genetic changes that helped them cope — or at least survive — despite the immunological costs.
By comparing ancient and modern genomes, the study provides a rare direct observation of selection in action. Unlike inferences based on patterns in contemporary DNA — which can be confounded by demographic history — ancient DNA offers a chronological record, allowing scientists to see when and how fast certain variants rose in frequency. This methodological strength is what enabled the researchers to distinguish true biological selection from the noise of population movements.
The findings contribute to a growing body of work showing that human evolution did not stop with the advent of agriculture or even industrialization. Instead, our genomes have continued to respond to pressures from diet, disease, and lifestyle — often in ways that are only now becoming visible through the lens of ancient DNA.
Why did the frequency of celiac-linked gene variants increase if they raise disease risk today?
The variants may have provided advantages in ancient environments — such as stronger immune responses to intestinal pathogens — that outweighed their costs, illustrating how evolution favors traits that enhance survival and reproduction in specific contexts, not long-term health.
How does this study differ from earlier ancient DNA research?
While much ancient DNA work focuses on tracking migrations and population mixtures, this study specifically examined how natural selection shaped human biology over time, treating ancient genomes as a record of adaptation rather than just demographic history.