In the late 1970s, anthropologists exploring a cave on the rugged coast of southern Greece found two mysterious hominin skull fossils. Time had left them fragmented and distorted, and the jumbled stratigraphy of the cave made them hard to date. For decades, the fossils sat on a shelf, their identity unknown. Now, a state-of-the-art analysis of their shape together with new dates suggest one skull might represent our own species, living in Greece more than 200,000 years ago. The findings, reported in Nature this week, would make this the oldest known Homo sapiens fossil found in Europe, by at least 150,000 years.
If so, H. sapiens's first forays out of its African cradle likely happened earlier and extended much farther than most paleoanthropologists thought, into territory dominated by Neanderthals, our extinct cousins. "And then [H. sapiens] disappeared" from Europe, says Eric Delson, a paleoanthropologist at the City University of New York in New York City, until a later wave successfully spread across the continent about 50,000 years ago. But because the evidence is no more than a piece from the back of the skull, some researchers aren't sure the fossil can be definitively identified as H. sapiens. And others question the old date.
Katerina Harvati, a paleoanthropologist at the University of Tübingen in Germany, has long suspected that southeast Europe was a hot spot for ancient humans. Not only is the region "at the crossroads of three continents"—Africa, Asia, and Europe—but it enjoyed a relatively mild climate when other parts of Europe were covered by glaciers, she says. So she was thrilled to receive permission to study the fossils, which are named for the cave. The first individual, Apidima 1, is represented by the skull piece. The second, Apidima 2, is more complete and includes the face.
The Apidima 1 skull fragment was more complete on one side than the other, and Apidima 2's skull and face were distorted. So Harvati began by figuring out what they originally looked like. She and her team scanned both fossils with x-rays and created 3D reconstructions. They digitally broke Apidima 2 into 66 bone fragments and painstakingly reassembled them into what was likely their original shape. The result showed the face of a typical Neanderthal, jutting from the skull and complete with protruding brow ridges. The ratio of uranium to its decay products in the bones revealed an age of about 170,000 years old.
For Apidima 1, Harvati and her team created a mirror image of the fossil and stitched the two together to see the full shape of the back of the skull. It was short and round, like the skulls of H. sapiens, and lacked a ridge and furrow that Neanderthal skulls typically have at the back. "You couldn't bend [the Apidima 1 reconstruction] into a classic Neanderthal cranium," agrees Christoph Zollikofer, a paleoanthropologist at the University of Zurich in Switzerland who wasn't involved in the research. Harvati and her team concluded that the skull most likely belonged to H. sapiens.
The finding startled Harvati herself—especially because the uranium dating of Apidima 1 put its age at 210,000 years old. That makes it at least 15,000 years older than the next oldest fossil of our species found outside of Africa, in Misliya Cave in Israel. It's about 100,000 years younger than the oldest known H. sapiens fossils in the world, from Jebel Irhoud in Morocco. But Warren Sharp, a uranium dating expert at the University of California, Berkeley, points out that the Apidima 1 samples actually returned dates ranging from more than 300,000 years old to less than 40,000 years old. "It's not a well-behaved sample," he says. "You have this huge spread of apparent ages, and you don't know if any of them are any good."
Researchers are also divided on whether Apidima 1 convincingly represents a member of our species. "[Apidima 1] pretty clearly preserves enough of the cranium to demonstrate that it is definitively Homo sapiens," Delson says. But not everyone agrees. "It's plausible," says Susan Antón, a paleoanthropologist at New York University in New York City. "But for me it's not a slam dunk."
In ancient humans, the shape of the back of the skull doesn't always predict the shape of the face, she says. The Jebel Irhoud skull, for example, has an archaic, elongated back but a distinctly modern face. Zollikofer adds that the Neanderthal lineage may encompass more anatomical variations than researchers yet realize—perhaps including a short, round skull. "It highlights the scarcity of our knowledge," he says. In fact, Marie-Antoinette de Lumley, a paleoanthropologist at CNRS, the French national research agency in Paris, has recently argued that both skulls are actually ancestors of Neanderthals.
Israel Hershkovitz, a paleoanthropologist at Tel Aviv University in Israel who found the fossils in Misliya Cave, thinks that because members of H. sapiens were in the Middle East about 200,000 years ago, they could have made an early excursion to southern Europe, too. Harvati points out that some Neanderthal genomes preserve a trace of an interbreeding event with H. sapiens that took place before 200,000 years ago, a sign that our ancestors must have entered Neanderthal territory early, before vanishing again. Perhaps "they didn't like the climate, or didn't like the fauna to eat, or didn't like having Neanderthals around, and pulled back," Delson says.
But Hershkovitz isn't convinced Apidima 1 represents those ancient pioneers. Without more complete fossils and confirmation of their dates by other techniques, he says, "The evidence is very weak."