Red hair and thinning hair: Study of ancient DNA shows human evolution has accelerated over the past 10,000 years

Some of the relatively recent genetic traits, such as red hair, might get carried along into descendant populations without actually being the effective cause of increased evolutionary fitness, researchers say. Photo by Clodagh Kilcoyne/Getty Images/File

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Something happened around 4,000 years ago in West Eurasia that made red-haired people more common.

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But not just redheads. New research shows genetic variants linked to celiac disease, schizophrenia, light skin, a lower chance of male pattern baldness, and B blood type all arose and caught on quickly among prehistoric humans because they gave some sort of evolutionary advantage. Genes relating to body fat and cognitive performance, and resistance to various diseases such as leprosy also saw major spikes in frequency around this time, and made those who had them more likely to pass their genes on to descendants.

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Other genetic variants relating to tuberculosis, arthritis and multiple sclerosis saw rapid decreases in frequency.

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It seems to have had something to do with the development of agriculture in this geographical area, roughly Europe and the Middle East, and with the changing evolutionary pressures that farming brought about, including changing diet and exposure to new diseases.

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The new research, published Wednesday, shows for the first time that hundreds of these rapid evolutionary adaptations in humans have occurred in just the past 10,000 years, far more than previously thought, and much more recently. Fewer than two dozen had previously been identified, the best known being a tolerance for lactose after infancy that evolved in European populations.

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The new study, by lead author Ali Akbari, a computational geneticist in the Harvard University lab run by co-author David Reich, is the largest of its kind in the newish field of ancient human genetics.

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It shows changes that happened for the first time among those West Eurasian human populations have major relevance to the health of modern day human populations all over the world, and it suggests human genetic evolution is not fixed in time but is in fact accelerating, the authors say.

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The majority of the newly discovered adaptations are related to disease risk, although it remains uncertain why each gene gave people an evolutionary advantage in the past.

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In a statement, Reich said this research “allows us to assign place and time to forces that shaped us.”

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DNA sequencing technology has in recent years allowed scientists to see more deeply into the finds of archeologists, and to track single genes as their prevalence rises and falls in various prehistorical populations whose members today are physically reduced to a few shards of teeth or bone.

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So, instead of looking in present-day human DNA for clues about how it evolved, or what Akbari calls “the scars of natural selection” that are visible on the modern human genome, this research shows they can instead track that selection over time.

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“Rather than being trapped in the present and studying the scars left by selection on the genomes of descendants, ancient DNA makes it possible to test directly whether frequencies of variants shifted more than could be expected by chance,” reads the paper in the journal Nature.