Finger fossil find in Saudi Arabia pushes back migration date

THE discovery of a fossilised human finger bone in the desert of Saudi Arabia, that archaeologists said was 85,000 years old, if confirmed, would be the first and earliest Homo sapiens fossil found on the Arabian Peninsula. It will also be the oldest specimen of our species to be directly dated outside Africa and its doorstep, the Levant.

Along with recent finds of 80,000-year-old human teeth from Asia and 65,000-year-old human relics from Australia, the finger bone provides further evidence that early modern humans spread out of Africa much earlier and farther than previously thought. “This discovery of a fossil finger bone 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 of the paper, which was published in Nature Ecology & Evolution, said. “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, which was at the heart of that dispersal from Africa into Asia, was a lush grassland awash in rivers and teeming with wildlife such as ostriches, gazelles and hippopotamuses. For over 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,” Huw Groucutt, an archaeologist from the University of Oxford and lead author of the paper, said.

In 2016, Iyad Zalmout, an archaeologist with the Saudi Geological Survey and author of 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 out from the sediment surface. Zalmout pulled up a cylindrical bone, barely bigger than an inch, that had a socket at one end and a protrusion at the other. A colleague 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 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 non-human primates like gorillas and chimpanzees. “These studies very strongly demonstrated that this finger bone belongs to a member of our species, Homo sapiens,” Groucutt said. The team suspects that the bone came from a middle finger, though they are not sure if it was from the right or left hand. 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.

So far, this finger bone is the oldest Homo sapiens fossil found outside of Africa and the Levant that has been directly dated. María Martinón-Torres, director of the National Research Centre on Human Evolution in Spain, 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.”

Nicholas St. Fleur