Ancient finger bone pushes back human migration from Africa

​London: Scientists have discovered a fossilised finger bone of an early modern human in Saudi Arabia, dating back to about 90,000 years, that may rewrite the history of our ancestors' migration out of Africa. Published in the journal Nature Ecology and Evolution, the discovery from the Nefud Desert of Saudi Arabia is the oldest directly dated Homo sapiens fossil outside of Africa and the Levant. It indicates that early dispersals into Eurasia were more expansive than previously thought. 

"This discovery for the first time conclusively shows that early members of our species colonised an expansive region of southwest Asia and were not just restricted to the Levant," said Huw Groucutt from the University of Oxford in the UK. "The ability of these early people to widely colonise this region casts doubt on long held views that early dispersals out of Africa were localised and unsuccessful," said Groucutt. 

Previously it was thought that early dispersals into Eurasia were unsuccessful and remained restricted to the Mediterranean forests of the Levant, on the doorstep of Africa. The finding from the Al Wusta site shows that there were both multiple dispersals out of Africa, and these spread further than previously known. "The Arabian Peninsula has long been considered to be far from the main stage of human evolution," said Michael Petraglia, a professor at the Max Planck Institute for the Science of Human History in Germany. 

"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. Numerous fossils were discovered at the site of Al Wusta, an ancient fresh-water lake located in what is now the hyper-arid Nefud Desert. 

Among these finds was a well preserved and small fossil, just 3.2 centimetre long, which was immediately recognised as a human finger bone. The bone was scanned in three dimensions and its shape compared to various other finger bones, both of recent Homo sapiens individuals and bones from other species of primates and other forms of early humans, such as Neanderthals. 

The results conclusively showed that the finger bone, the first ancient human fossil found in Arabia, belonged to our own species, researchers said. Using a technique called uranium series dating, a laser was used to make microscopic holes in the fossil and measure the ratio between tiny traces of radioactive elements, they said. 

These ratios revealed that the fossil was 88,000 years old. Other dates obtained from associated animals fossils and sediments converged to a date of about 90,000 years ago.