Ancient DNA has helped scientists reconstruct evolution and adaptation among humans living in Eurasia over the course of 30,000 years.
That lengthy period of evolution — starting about 85,000 years ago — would have aided human adaptation to changing climatic conditions so they could leave the middle east and migrate to colder climes across Asia and Europe.
The analysis of thousands of ancient genomic samples by scientists from the Australian National University, University of Adelaide, UNSW and UTS, shines a light on a period of stagnated human movement they describe as the ‘Arabian Standstill’.
“There are way more signatures of very, very strong adaptive evolution in humans than previously thought,” says the study’s co-lead author Dr Yassine Souilmi.
Evidence that human evolution driven by major environmental pressures discovered
This adaptive evolution appears to be a response to the arrival of humans in new locations, as well as natural changes to the climate.
As the genetic evidence of a shared evolutionary event is carried by most modern humans, this points to a momentary adaptation that occurred before groups left the mid-east and spread across the planet.
“In the general vicinity of the middle to near East, people have stagnated there for a good period of time until they actually adapted to the colder climates,” Souilmi says.
“That’s what we call the ‘Standstill’, so they’ve just hung around there – obviously it wasn’t an organised thing – and it’s that they expanded from there when it became advantageous or possible.
“And it’s very, very, very slow – we’re talking around 30,000 years, that’s three times longer than we’ve had farming.”
Certain genes were also found to be associated with adaptations across species.
Those which code for the development of cilia – minuscule hairy projections on cells that support lung health in cold and dry conditions – were found to be overrepresented among evolutionary events between both humans and other mammals like arctic foxes and polar bears. Similar adaptations were found in Inuit populations in Greenland.
“By bringing in that evidence, we can say it’s actually cold adaptation that’s the main driver. Then we map those [gene] targets back to the biological function,” Souilmi says.
Ancient markers answer modern questions
Among the markers identified as points of genetic adaptation were ones closely linked to modern-day conditions like diabetes, obesity and neurodegeneration.
Increases in ancient DNA availability are now starting to influence medical research, which can begin finding locations on the human genome that might be highly conserved over tens of thousands of years, and those which might show signs of sudden, adaptive changes among particular groups.
Souilmi says linking long-term genetic changes to unique characteristics is a tool health scientists can use to learn more about which parts of the genome perform specific functions.
“Medical research is up against a very, very big problem, which is the human genome – it’s three billion base pairs, it’s got about 19 to 20,000 genes… and a few other things in between.
“Only about 6000 of them [genes] are very well annotated, the rest of them – we’re actually not sure what they do.
“And so adaptation, while not a silver bullet to solve medical problems, you don’t have in a region of the genome coming under selection unless it has a phenotype.
“We don’t know what the phenotype is – so it’s a different problem – but it says at least telling us that that region is functionally important.”