Human evolution has accelerated since our ancient ancestors began farming to favour traits like red hair and lower body fat, according to a new study.
Led by researchers from Harvard University, the study analyzed DNA samples from nearly 16,000 ancient humans who lived in Europe and parts of the Middle East over a period of more than 10,000 years. In that time and region, researchers found that natural selection sped up for hundreds of genes linked to traits like hair colour, skin tone, body shape, disease resistance and behaviour.
“This work allows us to assign place and time to forces that shaped us,” senior author David Reich, a professor of genetics and human evolutionary biology at Harvard University, said in a news release.
From red hair to lower body fat
For the study, researchers spent seven years building a collection of DNA sequences from ancient people who lived in West Eurasia, which encompasses Europe and parts of the Middle East. Working with 250 archeologists and anthropologists, they logged new DNA data from more than 10,000 ancient humans. Researchers also analyzed previously-sequenced DNA data from around 5,800 ancient individuals and sequences from 6,400 modern humans to create the largest study of its kind.
“This single paper doubles the size of the ancient human DNA literature,” Reich explained. “It reflects a focused effort to fill in holes that limited the power of previous studies to detect selection.”
When the DNA from these ancient humans was analyzed using new computational methods, researchers were able to identify 479 gene variations that had spread or declined. Such genetic changes, they discovered, accelerated after the region began transitioning from hunting and gathering to agriculture, roughly 10,000 years ago.
The DNA variants that were identified are linked with physical traits like red hair, light skin tone and a lower chance of male-pattern baldness.
In terms of health, the genetic changes led to increased immunity to HIV infection and leprosy, a lower risk of rheumatoid arthritis and alcoholism, and an increasing prevalence of B blood types.
Changes associated with a reduction of harmful traits were also observed, including a lower risk of bipolar disorder and schizophrenia, lower body fat and waist-to-hip ratios, and a decreased risk of tobacco smoking.
‘Richness of variation’
Researchers say the results show that since modern humans arose in Africa some 300,000 years ago, our species has continued to evolve more than previously thought.
The study was published on Wednesday in the academic journal Nature.
The team now wants to look even further back in time as well as at the evolution of other populations around the world.
“To what extent will we see similar patterns in East Asia or East Africa or Native Americans in Mesoamerica and the central Andes?” Reich said.
“This paper shows how complex selection can be and provides an opportunity to consider the richness of variation in human populations.”
