If it wasn't for an extinct relative of modern humans known as the Denisovans, some researchers think our own species might never have made it to the highest and largest plateau in the world.
The Tibetan Plateau is often referred to as the roof of the world because it is 4,000 meters above sea level.
One of the last places where Homo sapiens settled permanently is the vast sweep of elevated land that cuts through China, Russia and Mongolia. There have been periods of occupation by various ancestors over the past 160,000 years, but there are gaps in the record.
Is it the case that people have always been on the roof of the world, or is it the case that each period is a new community resettling?
A geneticist and an Archeologist have suggested a new timeline that works with the limited evidence we have.
The researchers used both archaeological and genetic evidence to create two different models of occupation. The two models can be tested, which could tell us how far back modern populations are.
Humans spent tens of thousands of years on and off in the model.
Evidence supports permanent colonization that began between 30,000 and 40,000 years ago. If so, the long genetic line might have passed on some helpful tricks for living up where the air is thin.
A single crossbreeding event between Denisovans and H. sapiens in East Asia may have given our species the genes they needed to live in a low oxygen environment.
"Although we don't know if Denisovans were adapted to the high altitude, the transmission of some of their genes to us could be the game-changer thousands of years later for our species to get adapted to hypoxia," says Nicolas.
That is a great story.
It's not clear whether that's a true story.
Evidence shows Denisovans first appeared on the Tibetan plateau about 160,000 years ago. It's not known if these early humans made their home here all year round or just visited on occasion.
The same is true of our species. The first archeological evidence of H. sapiens is from 40,000 years ago, but it may have taken 11,000 years for continuous occupation to occur here.
The truth will only be figured out if we include genetic data.
Most modern Tibetans have a variation in the EPAS1 gene that helps them survive at high altitudes by increasing oxygen transport in the blood.
A Denisovan finger bone was found in the mountains north of the Tibetan plateau in 2010. Did Denisovans have a similar haplotype?
The short answer is that maybe. We don't have enough Denisovan to confirm.
According to the authors of the current paper, recent genetic research has shown that all East Asians, including Tibetans, have the same patterns of Denisovan DNA.
The interbreeding event which was specific to East Asians probably occurred between 46,000 and 48,000 years ago.
The genes they acquired from Denisovans in the lowlands are thought to have been the reason H. sapiens made it to the top of the world.
How long would it take for those genes to be selected for the East Asian population?
The quirk in the EPAS1 gene haplotype in modern Tibetans was positively selected between 2,800 and 18,300 years ago, according to research.
The genetic divergence of modern Tibetans and Han Chinese seems to have happened 30,000 years ago.
The authors of the current paper argue that we shouldn't rule out the possibility that H. sapiens lived on the Tibetan Plateau as far back as 40,000 years ago.
The authors say that the low-resolution data does not allow a complete validation of either hypothesis.
The models could show archaeological and genetic predictions for further studies.
The study was published in a journal.
