Ancient DNA Reveals Hitherto Unknown Aspects of Human Evolution

Ancient DNA from human remains that are around 45,000 years old has given scientists new insights into human evolution. It has enabled them to conclude that human populations fairly quickly adopted favorable genetic variants. Until now, this aspect of natural selection in human evolution has not been widely recognized.

Understanding the Tempo of Positive Selection in Human Evolution

The multinational study was published in the journal  Nature Ecology & Evolution . The study examined ancient  human genomes  to look at the role of natural selection in shaping biological diversity. So far, positive selection has mainly been studied using modern human genomic data which can be susceptible to distortions associated with unknown aspects of population history, in particular mixing of diverse population groups.

A report on the  University of Adelaide website  quotes Dr Souilmi as saying, “It was widely believed the genetics of our human ancestors didn’t change due to environmental pressures as much as other animals, due to our enhanced communication skills and ability to make and use  tools. However, by comparing modern genomes with ancient DNA, we discovered more than 50 cases of an initially rare beneficial genetic variant becoming prevalent across all members of ancient human groups.

“In contrast to many other species, evidence for this type of adaptive genetic change has been inconsistent in humans. This discovery consequently challenges the prevailing view of human adaptation, and gives us a new and exciting insight into how humans have adapted to the novel environmental pressures they encountered as we spread across the planet.”

Ancient Genomes Shed New Light on History of Human Evolution

According to the  University of Adelaide website , Dr Tobler explained that examining ancient human DNA had been critical to this fresh insight into human evolutionary history. “We believed historical mixing events between human groups might have hidden signs of genetic changes in modern human genomes. We examined DNA from more than 1,000 ancient genomes, the oldest which was around 45,000 years old, to see if certain types of genetic adaptation had been more common in our history than studies of modern genomes had suggested.”

Professor Christian Huber, an Adjunct Fellow at the University of Adelaide and an Assistant Professor at Penn State University, who is a senior author of the study added that using  ancient DNA  for the study was very important because it predated the major historical population mixing events that had radically altered  European genetic ancestry . This allowed them to capture historical signs of adaptation that cannot be obtained from an analysis of modern DNA.

Previous studies  indicated Europeans inherited blue eyes, lower cholesterol levels, a higher Body Mass Index (BMI), and darker hair colors from pre-migration hunter-gatherers. ( endrews21/ Adobe Stock)

The study team included researchers from the Mayo Clinic, the Garvan Institute of Medical Research, the Max Planck Institute for the Science of Human History in Germany, the University of New South Wales, and Massey University.

The Australian Centre for Ancient DNA was set up in 2005 for research and development of advanced ancient DNA for application in the fields of evolution, environment and conservation. 

Genomic datasets have rapidly become available to researchers studying human evolutionary history, accompanied by advances in statistical methods for detecting genetic signals of positive selection. However, such studies usually fail to account for past phases of interpopulation mixing that can alter genomic signatures and mask signals of positive selection, leading to faulty interpretations.

The University of Adelaide study has skirted this problem by examining ancient  DNA predating such human population intermixing events. It also studied three modern European population datasets to ascertain the impact of  Holocene admixture on modern European populations. This has allowed them to conclude that ancient human populations used positive selection and quickly adapted favorable genetic variants. As the paper published in  Nature Ecology & Evolution  states, “Through analyses of ancient and modern human genomes, we show that previously reported Holocene-era admixture has masked more than 50 historic hard sweeps in modern European genomes.”

Top image: Ancient DNA from human remains like this representation were used in the study. Source:  Erin Cadigan  / Adobe Stock

By Sahir Pandey