85,000-year-old bone suggests humans inhabited Arabia millennia before previously thought

A lone finger bone unearthed in the Saudi Arabian desert suggests modern humans had already penetrated deep into the Arabian peninsula 85,000 years ago, said a study published on Monday, that suggests humans may have left Africa millennia before previously thought.

The research, published in the journal Nature Ecology & Evolution, challenges a long-held consensus that humans started their exodus from our birthplace in Africa only about 60,000 years ago, with a few small, unsuccessful migrations before.

Recent archaeological finds have started to question that idea, with some claiming evidence of homo sapiens spreading beyond Africa and into the neighbouring Levant region already 120,000 years ago or more.

However, many of those discoveries - including from China and Australia - have doubts hovering over their authenticity and dating, said the authors of the study. 

Their new fossil finger bone discovery however, unquestionably belonged to a human and could be dated directly using radiometric technology, said the team. It is the oldest adult bone to ever be discovered outside of Africa. 

Its age served as rare evidence that "our species was spreading beyond Africa much earlier than previously thought," said study co-author Huw Groucutt from the University of Oxford.

The bone, just 3.2 centimetres (1.6 inches) long, is thought to be the middle bone of a middle finger, likely of an adult. It was discovered in the al-Nefud Desert of Saudi Arabia in 2016 by Dr. Iyad Zalmout, a paleontologist with the Saudi Geological Survey, and analysed over two years.

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Groucutt and a team used a form of radiometry called uranium series dating to determine the bone's age by measuring tiny traces of radioactive elements.

The tests revealed it was at least 85,000 years old - possibly 90,000 - making it the "oldest directly-dated homo sapiens" fossil ever found outside of Africa and the Levant, said the team.

Hunter-gatherer with tools

It is the first fossil of a hominin - the group of humans and our direct ancestors - discovered in present-day Saudi Arabia.

Other archaeological finds, which their discoverers claim are even older, may very well be authentic but were not directly dated, said the research team. Most had their age calculated from the sand or rock layers they were found in, or other items in the vicinity.

Besides redating the human exodus from Africa, the study may also alter its route.

"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.

The mainstream theory on how humans spread throughout the world, argues that humans left Africa in a single wave, moving along the coast from Africa via southern Arabia and India all the way to Australia.

The Levant consists roughly of the eastern Mediterranean area today covered by Lebanon, the Palestinian territories, Israel, part of Syria, and western Jordan.

However the finger, discovered far from the coast, shows "that modern humans were moving across the interior, the terrestrial heart, of Eurasia - not along the coastlines," said Petraglia.

The bone was discovered in an area known as Al Wusta that 90,000 years ago would have looked very different to the desert it is today - with plentiful rivers and lakes.

The team found fossils of various animals, including hippos, as well as advanced stone tools.

This all pointed to the owner of the finger having been a member of a semi-nomadic hunter-gatherer group moving after water and animals.