Two skulls chiselled from a slab of Greek rock have deepened our understanding of early humans living on the European continent.
The specimens were found in the Apidima Cave – a site etched into a seaside cliff – in Southern Greece in 1978. Their significance is only now being revealed, in a paper published in the journal Nature.
Both skulls – named Apidima 1 and Apidima 2 – were washed into a gap in the cave wall and then cemented into place thousands of years ago.
Despite being found just 30 centimetres apart in the same block of breccia, the new study reports that they aren’t the same age. Nor are they from the same species.
“Previous studies have all assumed that these two specimens were of the same geological age, but also the same taxonomic attribution,” says palaeoanthropologist Katerina Harvati from Eberhard Karls University of Tübingen in Germany, who led the study.
Harvati and her colleagues created careful 3D reconstructions of both skulls, and compared them, using a shape analysis technique known as geometric morphometrics, to other fossil specimens and modern-day human skulls.
The Apidima 2 skull, which includes the individual’s face and top of the head, is the more complete of the two, yet it is badly distorted and fragmented. Nonetheless, after virtual reconstruction, the shape analysis identified it as belonging to a Neanderthal.
Meanwhile, analysis of Apidima 1, which consists of an undistorted but smaller portion of the back of the skull, turns out to be one of our own – Homo sapiens.
“The shape of the skull is surprisingly rounded in side view – a modern human feature,” says Harvati. “However, it is the statistical, geometric morphometric shape analysis that brings home just how modern human-like this specimen is.”
Uranium-series dating of fossil fragments suggest that Apidima 1 is at least 210,000 years old. That makes it the oldest evidence of Homo sapiens in Europe.
The Neanderthal skull, Apidima 2, dates to 170,000 years ago.
Homo sapiens evolved in Africa. Skulls from the Jebel Irhoud site in Morocco that date to around 315,000 years ago are the oldest known evidence of modern humans.
But early modern humans didn’t just stay in Africa.
In 2018, a modern human jawbone from the Misliya Cave in Israel was found to be 177,000 to 194,000 years old. Stone tools from the site date back even further, to 274,000 years ago.
The Apidima 1 population may have dispersed from this population in Israel.
Neither of these populations went on to contribute to modern human genetics, however. Instead, they were part of an early wave of human migrations out of Africa that didn’t stick.
“Probably we’re seeing evidence of human dispersals that are not just limited to one major exodus out of Africa, as perhaps we have thought in the past, but multiple dispersals, the earliest ones of which did not necessarily leave a genetic contribution to modern Europeans or modern Eurasians living today,” says Harvati.
Modern humans with ancestry outside of Africa can trace their roots to a dispersal of Homo sapiens out of Africa much later, between 70,000 and 50,000 years ago, she says.
The earlier dispersals could have contributed genes to Neanderthals, as there is evidence in Neanderthals of an early interbreeding event with early humans.
Neanderthals probably trekked south to Greece and the middle east from further north in Europe at the height of the Ice Ages.
Whether Neanderthals and early modern humans ever met or co-existed in southern Greece is unknown. How and why modern humans died out in the area also remains a mystery.
“It’s a complex scenario of population dispersal, range contraction, and possibly also contact,” says Harvati.
Israel Hershkovitz from Tel Aviv University, who led the study of the Misliya specimens, is sceptical about the certainty of the Apidima skulls’ identification.
“There is no way to be absolutely sure they don’t belong to the same [species],” he says.
The lack of associated artefacts such as stone tools is also problematic, says Hershkovitz.
“The most important thing is to find the archaeological context,” he says. “Without it, you are working in the dark when it comes to the exact dating of the fossils.”
Nevertheless, Hershkovitz wouldn’t be surprised to find early modern humans in Greece that are as old as Apidima 1, given the similarity in climate and its proximity to Israel.
Harvati and her colleagues are continuing excavations at the site. And, despite the unfavourably warm and humid conditions at the site, they will also try to extract ancient DNA and proteins from the specimens to better nail down their relationship to other humans of the time.
They also hope to find more fossils in Greece and its surrounds, a region that palaeoanthropology has, until recently, neglected, says Harvati.
“The human fossil record of the region is hypothesized to be highly diverse and to reflect population movements, late survivals, range contractions and potential interactions among populations,” she says.
“We have not been able to really test these ideas. This study is, I hope, a first step in that direction.”
Related reading: Zlatý kůň: The oldest human genome