“This discovery of a fossil finger bone for me is like a dream come true because it supports arguments that our teams have been making for more than 10 years,” Michael Petraglia, an archaeologist from the Max Planck Institute for the Science of Human History in Germany and an author on the paper, which was published in Nature Ecology & Evolution, said during a media briefing.
“This find, together with other finds in the last few years, suggest that modern humans, Homo sapiens, are moving out of Africa multiple times during many windows of opportunity during the last 100,000 years or so,” he said.
Arabia was at the heart of that dispersal from Africa into Asia. But at the time when this ancient person lived, the Arabian Peninsula was almost alien from what it is today. Instead of being bone dry with endless red sand, it was a lush grassland awash in lakes and rivers and teeming with wildlife like ostriches, gazelles and hippos.
“Our study shows that the early spread of our species was aided by climate change and that humans spread into very diverse types of habitats as they moved beyond Africa,” Huw Groucutt, an archaeologist from the University of Oxford and lead author on the paper, said at a media briefing.
For more than a decade, the team had searched the vast desert for clues. They had dug up hundreds of stone tools, collected satellite imagery of thousands of paleolakes and found numerous bones belonging to wild cattle, antelopes and other animals.
“But one thing was always missing: ancient human fossils,” Dr. Groucutt said.
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. He spotted something white sticking halfway out from the sediment surface. Dr. Zalmout pulled up a cylindrical bone, barely bigger than an inch, that had a socket at one end and a protrusion at the other.
“I said: ‘What could this be? It doesn’t look like any other mammal that we’ve seen here before,’” said Dr. Zalmout.
He showed the find to a colleague, who suggested it may have belonged to a primate, possibly human. Back at the camp they compared it with images of Neanderthal finger bones, but it was much longer and thinner. They concluded it was most likely the phalanx, or middle finger bone, of a Homo sapiens.
Biological anthropologists from the University of Cambridge made a three-dimensional model of the bone, which they used in a statistical analysis to determine its origin. The test compared the bone with more than 200 finger bones belonging to humans, extinct hominins like Neanderthals and the ‘hobbit,’ Homo floresiensis, and nonhuman primates like gorillas and chimpanzees.
“These studies very strongly demonstrated that this finger bone belongs to a member of our species, Homo sapiens,” Dr. Groucutt said.
The team suspects that the bone came from a middle finger, though they aren’t sure if it was from the right or left hand. They also ruled out the possibility of extracting ancient DNA from the specimen because the arid environment most likely destroyed any genetic material, they said.
To determine how old the bone was, the team sent it to Rainer Grün, a dating specialist at Griffith University in Australia, who had previously helped date a 180,000-year-old jawbone from an Israeli cave.
Using a laser, he and his colleagues drilled seven microscopic holes into the bone. When the bone was buried, it absorbed uranium, which can be measured and provide a minimum age estimate. The fossil came back as being about 88,000 years old. The team also dated a hippopotamus tooth, stone tools and sediments, which provided similar date ranges of about 85,000 to 90,000 years.
Dating sites of ancient human occupation can be controversial because often they rely only on measurements of sediments where human remains were found and not the remains themselves.
“But here we’ve dated both the deposits and the fossil finger bone directly,” Dr. Petraglia said. “And so we think we have a very, very strong case to make in terms of the dating of this site.”
So far, the finger bone from Al Wusta is the oldest Homo sapiens fossil found outside of Africa and the Levant that has been directly dated.
Dr. María Martinón-Torres, the director of the National Research Center on Human Evolution in Spain said the team’s dating techniques were solid.
“Homo sapiens fossils with reliable dating and context around this period, outside Africa, are very scarce,” she said. “This is the type of solid evidence we need to challenge some models that were close to becoming a dogma rather than a scientific hypothesis, like the recent ‘Out of Africa’ model.”
For Dr. Petraglia, the finding opens up an opportunity for further exploration of Saudi Arabia’s ancient past. Because the country has historically closed itself off from foreign researchers, its role in modern humans’ early migration story has been largely underrepresented.
Ahmad Bahameem, a member of the Saudi Geological Survey said he was optimistic about future Homo sapiens discoveries from the Arabian Peninsula.
“This fossil is just a piece of a whole skeleton, like a drop of rain,” Mr. Bahameem said. But, he added, “the rain is coming.”