Evolution still shaping modern humans
A sweeping genetics study suggests that human evolution has not slowed in recent millennia. By analysing DNA from nearly 16,000 ancient individuals and more than 6,000 living people, researchers found clear evidence that natural selection has continued to shape populations in West Eurasia.
Among the most striking findings is that genetic variants linked to red hair and fair skin have been actively selected for more than 10,000 years. The study did not aim to explain why this occurred, but it challenges the long-held assumption that major evolutionary changes largely stalled after the rise of agriculture.
Hundreds of genes influenced by natural selection
The team identified 479 genetic variants that appear to have been favored over time. In addition to traits associated with red hair and lighter skin, the researchers observed increases in variants connected to coeliac disease susceptibility and decreases in genes associated with diabetes, baldness and rheumatoid arthritis.
Previous research had documented only about 21 clear examples of recent directional selection in humans, including the well-known ability to digest milk in adulthood. The limited evidence led some scientists to believe evolution had largely plateaued after modern humans dispersed from Africa roughly 300,000 years ago.
This new analysis, using a much larger ancient DNA dataset and advanced computational tools, suggests otherwise. According to Dr Ali Akbari of Harvard University, the techniques now allow scientists to “watch how selection shaped biology in real time.”
Possible advantages in ancient environments
Some evolutionary patterns appear intuitive. Variants associated with red hair and fair skin may have supported improved vitamin D synthesis in regions with low sunlight, particularly among early farmers whose diets lacked sufficient vitamin D.
Other findings are more complex. A mutation strongly linked to coeliac disease first appeared around 4,000 years ago and has steadily increased in frequency. Despite raising the risk of autoimmune problems, carriers may have gained survival advantages in certain historical contexts.
Similarly, a variant of the immune gene TYK2, which increases susceptibility to tuberculosis, rose in frequency between 9,000 and 3,000 years ago before declining. Researchers suggest that some disease-associated genes may have provided protection against other pathogens prevalent at the time.
The study also detected negative selection against combinations of genes promoting high body-fat levels. This supports the “thrifty genes” hypothesis: traits that once helped hunter-gatherers survive food scarcity may have become disadvantageous after agriculture ensured more stable food supplies.
Senior author Prof David Reich noted that the work allows scientists to assign both place and time to evolutionary forces. While the analysis focused on West Eurasia, it remains unclear whether similar trends occurred globally. The findings were published in the journal Nature.