88,000-Year-Old Finger

Ancient finger brings new questions
about human habitat and migration

It’s just a lone, boney finger, but the scientists who found it say it’s the oldest directly dated fossil of our species to ever be found outside of Africa and the Levant, a region that today comprises Israel, Syria, Lebanon, and Jordan. In 2016, Iyad Zalmout, a scientist with the Saudi Geological Survey, was participating in the Al Wusta archaeological dig in the Nefud Desert, the former site of an ancient freshwater lake in what is now the barren Arabian desert, when he discovered the ancient finger.

Two years prior, archaeologists had discovered the site, finding fossilized animal bones and troves of stone tools, tantalizing clues that hinted at former human occupation. Upon Zalmout discovering the human finger, he hurriedly grabbed the attention of the project leaders, Huw Groucutt from the University of Oxford and Michael Petraglia from the Max Planck Institute for the Science of Human History.

The finger, along with other samples found at the Al Wusta site, then traveled to the Australian National University in Canberra where scientists used several dating techniques to age the specimen, including uranium series dating, in which a laser pokes microscopic holes into the fossil to measure the ratio between traces of radioactive elements. The finger, the Australian researchers concluded, was 88,000 years old. The results of this study were published in Nature Ecology & Evolution.

That makes it the oldest directly dated fossil of Homo sapiens to be found outside of Africa and the Levant, the term “directly dated” being of crucial importance. Ancient human-like fossils and artifacts have been found elsewhere in east Asia and Australia, along with the remarkable but highly contentious discovery of 120,000-year-old human fossils in China. But in these cases, the human origin of the fossils isn’t entirely clear, and the items were indirectly dated, meaning the deposits enclosing the fossil or artifacts were dated, and not the fossil itself.

That anatomically modern humans were living in Saudi Arabia some 88,000 years ago is actually quite unsurprising. A jaw fossil found in Israel’s Misilya Cave, just a few hundred miles to the north, suggests ancient Homo sapiens were living in the Levant as long as 175,000 years ago, and possibly as long as 200,000 years ago. But what makes this new study exciting is that it’s the first direct evidence of early modern humans venturing outside of Africa and the Levant. What’s more, it affirms that migrations into Eurasia were more expansive than previously thought.

Traditionally, scientists figured modern humans migrated out of Africa in a single wave some 50,000 to 70,000 years ago, moving along the coast and subsisting off marine resources. But the discovery of this finger bone suggests humans were moving about 20,000 to 25,000 years earlier than assumed. “The discovery of this fossilized finger bone is a dream come true,” said Petraglia. “This find supports a model of not a single rapid dispersal, but a much more complicated scenario of migration. Combined with other discoveries made in the last few years, this suggests humans moved out of Africa multiple times during many windows of opportunities in the last 100,000 years or so.”

Interestingly, the fossil was discovered in the harsh Arabian desert, but back then the region was home to a very favorable environment, featuring humid and monsoonal weather conditions, extensive grasslands, rushing rivers, and sprawling lakes. In addition to the human finger, the researchers found fossilized traces of hippos and freshwater snails. For these early humans, the Levant and the Arabian region was merely an extension of Africa, with climate change and dynamic environmental conditions pushing and pulling them away from their continent of origin. As prey animals migrated, so too did these early humans. By adapting to this semi-arid grasslands in the Arabian interior, these early humans were setting the stage for a larger, more global expansion, according to the researchers.

As for the finger, the researchers don’t know the former owner’s gender or age, nor which hand it came from, but it does exhibit signs of manual stress. A lump in the bone has been interpreted as an injury caused by repetitive physical activity, perhaps from knapping stones into tools. However, doubt remains to whether the bone is actually from a human or not.

Anthropologist Rolf Quam from Binghamton University and Katerina Harvati, head of paleoanthropology at the Senckenberg Center for Human Evolution and Paleoenvironment, likes the new study, saying the authors did all they could to analyze the finger bone. “However, a finger bone is not very informative: a lot of overlap exists between the anatomy of modern human and, for example, Neanderthal, finger bones,” Harvati stated. “That being said, the results of their analysis strongly suggest that this bone indeed belonged to a human. Quam added, “In the end, I think we can’t say for sure what species this finger bone represents.”

Jean-Jacques Hublin, director of the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology, disagrees, saying the finger appears to be anatomically human, and that it does not contain any features usually found in Neanderthals. Hublin’s issue with the analysis, however, has to do with the uranium series technique, a dating method that he believes “is not very reliable on bone.” The dating of the surrounding deposits, which have been timestamped to 90,000 years ago, provide a “safer chronological position” in his opinion.