Ancient DNA Shows That Human Evolution Never Slowed Down — It Sped Up After Farming
Natural selection is generally a term reserved for science textbooks and not for conversations about contemporary humans. For decades, scientists believed that human evolution largely slowed after our species spread across the globe. But a new analysis of ancient DNA, published in Naturesuggests the opposite.
According to the new study, natural selection has not slowed down, but has accelerated.
By analyzing nearly 16,000 genomes spanning 10,000 years, researchers found that hundreds of genetic variants evolved much more recently than previously thought, many of them with distinct links to modern health and disease.
“This work allows us to assign a place and time to the forces that shaped us,” David Reich, lead author of the study, said in a press release.
How natural selection accelerated
At the heart of this study is a concept called directional selection. This form of natural selection occurs when a specific version of a gene becomes more common over generations because it improves survival or reproduction.
Previously, researchers had identified only a handful of such cases in ancient human DNA, suggesting that this process was relatively rare in recent human history.
However, the new research turns this idea on its head. Instead of a few isolated examples, scientists discovered 479 genetic variants that were heavily favored – or actively eliminated – in Western Eurasian populations over the past 10,000 years.
“This single paper doubles the size of the ancient literature on human DNA. It reflects a focused effort to fill gaps that limited the power of previous studies to detect selection,” Reich explained.
Many of these genetic changes are still visible today. Some are linked to physical traits like lighter skin or red hair, while others influence health outcomes, including reduced risks of illnesses like bipolar disorder or alcoholism.
One of the most significant findings is that natural selection intensified after humans moved from hunting and gathering to agriculture. As lifestyles have changed, so have evolutionary pressures, favoring traits better suited to agricultural diets, denser populations, and new disease environments.
Learn more: A single DNA letter change can cause female mice to develop testes
Innovative methods behind the breakthrough
Researchers spent seven years assembling one of the largest ancient DNA datasets ever compiled, combining genetic material from more than 10,000 newly analyzed individuals with thousands of previously studied genomes.
The real breakthrough came from new computational techniques designed to isolate the true signals of natural selection. In ancient populations, gene frequencies can change for many reasons. To address this problem, the team developed methods to distinguish true evolutionary pressure from these other factors.
“Thanks to these new techniques and the vast amount of ancient genomic data, we can now observe in real time how selection has shaped biology,” said first author Ali Akbari. “Instead of searching for the scars that natural selection leaves in today’s genomes using simple models and hypotheses, we can let the data speak for themselves. »
What this means for future ancient DNA research
Given that more than half of the identified genetic variants are linked to modern traits and disease risks, this research opens new avenues for studying human health. By tracing where certain genetic traits became common, scientists could better understand why certain populations are more sensitive or resistant to specific conditions.
The researchers made their data and methods public, paving the way for similar analyzes in other regions and time periods.
“To what extent will we see similar patterns in East Asia or East Africa or among Native Americans in Mesoamerica and the central Andes? If we cannot use ancient DNA to study the most important period of human evolution 1 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,” Reich concluded.
Learn more: Neanderthals mated with modern human women – and it still shapes the DNA of many people today
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