Ancient DNA reveals migrations and exchange

Advances in ancient DNA sequencing are shedding light on the genetic links between our Stone Age ancestors and modern humans, say Chinese researchers, allowing researchers to untangle the twisting branches of the human family tree.

In a paper published in Trends in Genetics, scientists at the Chinese Academy of Sciences in Beijing summarise this flood of new research, reviewing analyses of the genomes of 24 individuals who lived in pre-agricultural Eurasia between 45,000 and 7,500 years ago. They outline new insights covering how ancient modern humans are related to present-day humans, how the populations migrated and interacted with each other, and how they interbred with archaic hominins such as Neanderthals and Denisovans.

The review found at least four distinct populations: Europeans, Asians, and two that did not contribute substantially to present-day populations. By between 14,000 and 7500 years ago, unexpected genetic connections were found between individuals from opposite sides of Eurasia, providing evidence for greater interactions between these geographically distant groups — likely due to climate and cultural change.

“We can now see the presence of multiple distinct subpopulations in Europe and in Asia, and these in turn contribute different amounts of ancestry to more recent sub-populations,” says Qiaomei Fu, co-author of the paper and a paleogeneticist at the Chinese Academy of Sciences.

Between 45,000 and 7500 years ago, modern humans — our ancestors — were spreading out across Eurasia, while archaic hominins were disappearing. However, the study highlights evidence that humans mixed with Neanderthals on two major occasions, 60,000 to 50,000 years ago and again around than 37,000 years ago. Although the genomes of Europeans show a gradual decline in archaic ancestry from 37,000 to 14,000 years ago, Neanderthals were still found to contribute to the modern human genome.

According to biological anthropologist Michael Knapp at the University of Otago, New Zealand, the ability to analyse early modern human genomes has resulted in “new and exciting insights into our ancestry, with new findings sometimes coming out on a monthly basis”.

Knapp, who was not involved in the study, says that new research will quickly overtake this review, but “that is part of what makes the field of human palaeogenomics so exciting at the moment”.

Improved sequencing technology and computing resources make the present a great time for studying human evolutionary genetics, according to Fu: “There is huge potential to understand the biology of human prehistory in a way that has never been accessible before.”

In the future, the team plan to use this type of sequencing to study the history of populations in East Asia, Oceania, Africa and the Americas.

“Any ancient DNA from those continents will likely resolve some major questions on human migration,” Fu concludes.

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