DNA Influenced More by Natural Selection Than Previously Thought

A new extensive study suggests that our DNA has been shaped by natural selection in ways we didn’t fully appreciate, with gene variants linked to traits like red hair and pale skin being among those favored for survival.

Led by researchers from Harvard University, the study provides fresh perspectives on human evolution in relatively recent history.

This insight indicates that our evolutionary journey is still ongoing.

Often described as “survival of the fittest,” natural selection posits that organisms best adapted to their environment tend to reproduce more successfully, passing on their genes.

Previously, scientists believed that after transitioning from hunting to farming, our genetic evolution had stagnated. Past research identified only 21 genomic locations influenced by natural selection in Europeans over the last 10,000 years.

However, this new research uncovers that number to be in the hundreds: 479 genetic variants appear to have been strongly selected either for or against. Apart from variants affecting hair color and skin tone, the team also noted variants linked to disease risks and psychiatric traits.

“This single paper essentially doubles the body of ancient human DNA literature,” noted geneticist David Reich from Harvard.

“It reflects a concentrated endeavor to address gaps that previously limited detection of selection.”

The findings stem from analyzing an unusually large set of ancient genomes, involving nearly 16,000 individuals from the last 10,000 years in West Eurasia, alongside a new computational approach to track genetic variant trends over time.

The method employed by researchers isolates genes influenced by natural selection by examining relationships among individuals, including data from over 6,000 living people, to rule out migration or random chance as factors impacting survival.

While the study didn’t pinpoint specific reasons for the emergence of these variants, the researchers have some hypotheses.

For example, variants of the MC1R gene, known to be associated with red hair and pale skin, might have prospered due to lighter skin’s ability to absorb vitamin D more efficiently in sunlight.

This trait may have grown more advantageous as humans shifted from a hunting diet to a farming one, which featured more plants and grains. Sun became a crucial source of vitamin D, leading to potential adaptations in Europeans’ skin—though, of course, this remains an hypothesis.

Identifying gene variants selected for survival or reproductive advantage is quite challenging. Still, this new method illuminates ways to uncover natural selection’s influences.

“To reveal changes in genetic variant frequencies over the last ten millennia that exceed chance expectations, we need to detect subtle effects, necessitating thousands of genomes from that period,” explained Reich.

The researchers observed that some identified variants functioned collectively while others fluctuated over time—not all variants maintained robustness against change like those associated with red hair and pale skin.

Even with these advancements, the researchers stress a cautious approach to interpretation. Traits related to specific genes may not remain constant over millennia, and many elements of contemporary life lack direct ancient counterparts.

The team believes there’s still much more to uncover. They’ve made their analytical methods available for further research, which could be applied to DNA from other global regions, potentially shedding light on disease risks.

“With our new techniques and vast collections of ancient genomic data, we can now observe how selection has influenced biology in real time,” remarked geneticist Ali Akbari from Harvard.

“Instead of relying on simple models and assumptions to find the signs of natural selection in present-day genomes, we can let the data drive our understanding.”

The research has been published in Nature.