Redheads have spent centuries as the subject of folklore and a disproportionate number of Halloween costumes. Now, science is handing them a win. A sweeping new study out of Harvard found that natural selection has been actively pushing red hair genes forward for thousands of years, and the trend is still going.
The research, published inNatureand led by Harvard geneticist David Reich, is one of the largest ancient DNA studies ever conducted. Reich's lab spent seven years assembling DNA sequences from ancient people who lived across Europe and parts of the Middle East, ultimately combining newly reported data from over 10,000 ancient individuals with thousands of previously published sequences and modern genomes, covering nearly 16,000 people across 18,000 years of history. "This single paper doubles the size of the ancient human DNA literature," Reichsaid.
What the data revealed upended a long-held assumption in evolutionary biology. Scientists had largely believed that directional selection, the process by which natural selection consistently favors one trait over others, was rare in humans. The new analysis identified hundreds of instances of it, far more than the roughly 20previously documented cases.
"Perhaps having red hair was beneficial 4,000 years ago, or perhaps it came along for the ride with a more important trait," the study noted. Either way, the gene stuck around and spread.
The research found that genes linked to lighter skin tones and certain health-related traits also increased over time.
For a long time, the working theory was that once humans figured out agriculture, medicine, and technology, the brutal pressure of natural selection eased up. This study disagrees. Evolution didn't plateau after the advent of farming — it just found new pressure points. Lead author Ali Akbari, a senior staff scientist in Reich's lab, put it this way: "With these new techniques and a large amount of ancient genomic data, we can now watch how selection shaped biology in real time."
Reich got to the point. "This work allows us to assign place and time to forces that shaped us," he said. The team plans to take the research to East Asia and East Africa next, hunting for additional genetic variations that could eventually help with disease prevention. The redheads, for their part, can enjoy the moment.