"What we're arguing here is that there were multiple dispersals out of Africa, so the process of the movement and the colonisation of Eurasia was far more complicated than our textbooks tell us", said study co-author Michael Petraglia of the Max Planck Institute for the Science of Human History in Germany.
In 2016 their colleague Iyad Zalmout, an archaeologist with the Saudi Geological Survey and author on the paper, was prospecting in a site called Al Wusta in the Nefud Desert in the northern part of the Arabian Peninsula.
85,000 years ago, the Al Wusta site was rich grassland covered by permanent freshwater lakes, as Arabia's climate was wetter than it is now.
"We know that shortly after they lived, the rains failed and the area dried up".
A basic visual examination suggested it belonged to Homo sapiens, Groucutt said. The small finger bone was a brief glimpse into a slice of time from so long ago.
In order to confirm that the fossil was human and not Neanderthal or another relative species, the researchers scanned the fossil in three dimensions.
What remains a mystery is whether the fossil finger belonged to a male or a female. This is how the researchers dated the fossil and found that the finger bone was approximately 88,000 years old. There they found the middle bone of a middle finger. But 90,000 years ago, there would have been a large river and an extensive fertile area that welcomed plants, animals and even humans.
"And that makes sense when you think these guys are making [and using] stone tools so they're really using their hands to do a lot of hard, manual labour".
Arabia was at the heart of that dispersal from Africa into Asia.
"This discovery firmly puts Arabia on the map as a key region for understanding our origins and expansion to the rest of the world", said Petraglia, who led the project.
The exhumation began at Al Wusta.
"With the finding in Al Wusta, I would say that presence of Homo sapiens in Asia before 50,000 to 60,000 years ago is out of doubt, and we can now move on to the next questions: how and why modern humans left Africa and why they took so long to enter Europe", she said. This fossil proves those claims wrong and shows that humans first dispersed further than was thought. The researchers found at least 860 animal bones, and the most common were water-loving animals like hippos and buffalo.
"They're coming up against animals that they've never seen before; environments they've never seen before", he said.
"This discovery for the first time conclusively shows that early members of our species colonized an expansive region of southwest Asia and were not just restricted to the Levant", said lead author Dr. Huw Groucutt, from the University of Oxford in the United Kingdom and the Max Planck Institute for the Science of Human History in Germany. Genetic studies show that humans may have made it to Eastern Asia as early as 80,000 years ago.
The study was published online today (April 9) in the journal Nature Ecology & Evolution.