Ancient DNA from West Eurasia has revealed that, over the last 10,000 years, the human genome has been affected by natural selection far more than previously suspected, according to groundbreaking recent research.
The study, led by Harvard University researchers, analyzed almost 16,000 ancient DNA samples for their new human genome paper published in Nature, revealing that, instead of the expected dozens of genes affected, hundreds appeared to result from recent natural selection.
Studying ancient DNA reveals more than esoteric knowledge of the past; it explains current health issues by showing that parts of the human genome that are today strongly associated with disease risks once provided a now-unknown survival benefit.
Advancing the Human Genome
This is far from the first study investigating how ancient DNA relates to the modern human genome. Since the first recovery of ancient human genomic data in 2010, the field has grown rapidly, aiming to identify genetic relationships between populations over time. Early research identified only about 21 examples of extreme traits—such as lactose tolerance—that spread so widely they came to dominate populations.
In this scenario, when a specific extreme trait confers a strong reproductive advantage, it is known as directional selection. Most previous evidence suggested that, since humans left Africa roughly 300,000 years ago and diverged into separate populations, directional selection had become extremely rare.
The new research challenges that assumption, suggesting that directional selection has actually increased in the human genome since the end of the last Ice Age. This conclusion was made possible through new computational tools capable of analyzing unprecedented volumes of genomic data.
Entering the Human Genome
Interestingly, while these gene variants must have once offered some advantages, many are now associated with conditions such as lactose intolerance, type 2 diabetes, and schizophrenia. Exactly what benefits they once provided remains unclear, potentially obscured by differences between modern lifestyles and those of our ancient ancestors.
Research into how these genes entered the human genome could provide essential clues for understanding—and potentially treating—health conditions with genetic roots.
“With these new techniques and a large amount of ancient genomic data, we can now watch how selection shaped biology in real time,” said lead author Ali Akbari, a senior staff scientist in the lab of Harvard geneticist David Reich. “Instead of searching for the scars natural selection leaves in present-day genomes using simple models and assumptions, we can let the data speak for itself.”
“This work allows us to assign place and time to forces that shaped us,” said senior author David Reich, professor of genetics in the Blavatnik Institute at Harvard Medical School and professor of human evolutionary biology in the Harvard University Faculty of Arts and Sciences.
New Ways to View the Human Genome
The study introduced two major innovations that enable scientists to analyze genomic data more clearly and at larger scales. The first involved data collection, with the Reich Lab assembling a vast archive of European and Middle Eastern DNA, including more than 10,000 newly sequenced ancient samples, nearly 6,500 modern samples, and close to 6,000 previously published ancient DNA sequences.
“This single paper doubles the size of the ancient human DNA literature,” Reich explained. “It reflects a focused effort to fill in holes that limited the power of previous studies to detect selection.”
The researchers also developed an important computational tool to analyze the data, capable of readily distinguishing directional selection from other mechanisms of gene frequency change, such as population mixing.
“Ali developed a powerful technique that could zoom in on the patterns that actually mattered,” said Reich.
Analysis Results
While the team’s findings indicate that only 2 percent of the human genome is under directional selection, this still represents a significant portion of DNA. Akbari identified 479 gene variants that were strongly selected for or against within the dataset, and was even able to determine when and where some of these variants entered or exited the West Eurasian genome.
Although the new computational method streamlined the identification of directional selection, researchers say nearly 8,000 additional signals remain unclear and require further study to determine whether they are also the result of directional selection.
The Harvard team believes that continued research across the broader human genome will reveal similar evolutionary pressures in other populations. The dataset has been made publicly available for further analysis.
“To what extent will we see similar patterns in East Asia,” Reich asks, “or East Africa or Native Americans in Mesoamerica and the central Andes?”
“If we can’t use ancient DNA to study the most important period in human evolution, 1 million to 2 million years ago, then at least we can study selective pressure on human genomes during more recent periods of change and learn broader principles.”
The researchers noted that one key takeaway from the study is that removing gene variants associated with negative outcomes may be more complex than previously thought—especially if the original advantages those variants conferred remain unknown.
The paper, “Ancient DNA Reveals Pervasive Directional Selection Across West Eurasia,” appeared in Nature on April 15, 2026.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.