A study led by Harvard geneticist David Reich found evidence that natural selection has favored the gene responsible for red hair, contributing to its increased prevalence over thousands of years. The research, published in the journal Nature, challenges the assumption that human evolution has largely stopped in recent history.
Nearly 16,000 genomes, 10,000 years of history
The Harvard team assembled DNA sequences from ancient people across Europe and parts of the Middle East, combining data from more than 10,000 ancient individuals with thousands of previously published sequences and modern genomes — nearly 16,000 people in total, spanning roughly 10,000 years of human history.
A new method to detect evolution in progress
Researchers developed a new statistical method to isolate directional selection — the persistent trend of a genetic trait becoming more or less common in a population over time. This method allowed them to detect signals of evolutionary change that previous techniques couldn’t pick up, effectively proving that human evolution hasn’t slowed down; earlier methods were just missing the signal.
Why would red hair be favored?
The gene most strongly linked to red hair and pale skin is MC1R. Researchers believe these variants may have spread because pale skin absorbs vitamin D from sunlight more efficiently — an advantage that could have become more important as humans shifted from a hunter-gatherer diet to a farming diet higher in grains and lower in vitamin D-rich foods. The study also found selective advantages in genes linked to reduced male-pattern baldness, suggesting both traits may have influenced reproductive success in certain populations.
What it means going forward
Red hair remains relatively rare globally and is most concentrated in populations of European descent, but the study’s authors say its prevalence is measurably increasing due to ongoing natural selection — not by chance. The findings add a significant case study to broader efforts to map human genetic evolution, illustrating that specific physical traits are still actively shaped by a mix of environmental, cultural, and genetic forces well into the present day.
