Two skulls found in a Grecian cave paint a surprising portrait of who lived there hundreds of thousands of years ago. One fragmentary skull has been dated to 210,000 years ago, and researchers believe that it is the earliest evidence of modern humans living in Eurasia, according to a new study. The other, more complete skull belonged to a Neanderthal who lived 170,000 years ago.
Finding both in the same cave illustrates that multiple early migrations out of Africa, rather than a single event, helped early humans spread, according to the researchers. Southeast Europe is considered to be one of those major migration corridors out of Africa.
The study was published in the journal Nature on Wednesday.
Both skulls were found in a block of breccia, or broken fragments of rock and fossil cemented together, wedged high between the walls of the Apidima Cave in southern Greece. The skulls were discovered in 1978, when the National and Kapodistrian University of Athens was conducting research.
The breccia was dated to between 100,000 and 190,000 years old at the time. The skulls were not removed from the breccia and remained at the museum. Given the fragmentary nature of the skulls, they were difficult to remove and clean, though that eventually happened in the 1990s.
Apidima 1 was in pieces, and Apidima 2, the most complete skull belonging to the Neanderthal, was distorted. At the time, researchers focused on the latter. It had all of the characteristics of a Neanderthal, like a thick and rounded brow ridge.
Researcher Katerina Harvati and her colleagues, who focus on reevaluating the existing fossil record with cutting-edge dating techniques, were invited to study the Apidima fossils.
They scanned the fossils and created 3D reconstructions of them. The shape of each skull was compared with those of other species from the fossil record.
Apidima 2, which is essentially just the facial region of a skull without the lower jaw, matched yet again as a Neanderthal skull, despite its distortion.
Apidima 1, just the back of a skull, was fragmented but not distorted, so the researchers were able to use mirroring to re-create it.
The researchers were surprised to find all of the signatures of an early member of the Homo sapiens family in the Apidima 1 skull. The rounded back is just like a modern human's; Neanderthals have a bulge at the back of the skull that almost resembles a hair bun.
The oldest known fossils of early humans were found at Jebel Irhoud in Morocco, dating to 315,000 years ago. But the Jebel Irhoud fossils display more primitive features than Apidima 1.
Apidima 1 is now the oldest known European modern human fossil, 160,000 years older than previous discoveries.
The researchers also used uranium-series dating to determine the ages of each skull, putting Apidima 1 at 210,000 years old and Apidima 2 at 170,000 years old. Previously, it had been assumed they would both be the same age, given that they were found in the same breccia and only the breccia was initially dated.
But the cave system where they were found allowed for the remains of humans and animals from different time periods to accumulate.
The cave is reachable only by water now. At the time when modern humans and Neanderthals lived there separately, sea levels were lower. The cave overlooked a coastal plain that was probably perfect for hunting, while the cave itself provided shelter. Southern Greece would have been attractive during glacial times, offering a milder climate, the researchers said.
Given the fact that the modern human skull is older than the Neanderthal skull, which was unexpected, researchers believe that a group of modern humans lived in the area but didn't thrive. Climactic events or competition from Neanderthals caused them to die off, leaving no genetic trace behind in the population. Without further evidence, it's difficult to know what happened to them.
Then, Neanderthals lived in the area. And about 40,000 years ago, the last of the Neanderthals died off, and modern humans thrived.
Previous discoveries of early modern human fossils in Israel, dated between 90,000 and 194,000 years ago, could also represent populations that failed to thrive after leaving Africa.
Many questions remain for the researchers. They want to know the underlying cause for the early migrations, if there were technological advancements that allowed for those migrations and why some of the modern human populations didn't persist in the areas where they migrated.
They were also unable to recover DNA from the skulls but will analyze ancient proteins that could be preserved in the fossil, a method known as palaeoproteomics.