A few fossilized bones from the back of a skull may prove that our species spread into Eurasia much earlier than previously suspected. A new study of the partial skull, which was excavated from Apidima Cave in southern Greece 40 years ago, suggests that the fossil is Homo sapiens and that it’s roughly 210,000 years old. That makes it the oldest member of our species ever found outside of Africa.

The fossil, known as Apidima 1, is likely the remains of a member of an early wave of humans who spread into Eurasia. Based on genetic studies and the fossil record, anthropologists think these early pioneers failed to gain a successful foothold and ended up being replaced by Neanderthals (for a while, at least).

A new look at an old skull

Archaeologists excavating Apidima Cave in the 1970s found the partial skull lodged in a chunk of breccia, just a few centimeters away from a broken and distorted Neanderthal skull called Apidima 2, which dated to 170,000 years old. For decades, archaeologists assumed Apidima 1 was a Neanderthal, too. But Eberhard Karls University of Tübingen paleoanthropologist Katerina Harvati and her colleagues recently took a second look at Apidima 1. The partial skull included just the right pieces of bone to reveal something important: the skull was rounded at the back—a feature that’s unique to Homo sapiens.

And according to uranium-series dating, the skull could be as much as 210,000 years old. That’s a few thousand years older than Misliya-1, the previous holder of the Oldest Human Outside Africa title (at 194,000 to 177,000 years old). It fits pretty well with the growing pile of evidence that the earliest humans (like many of our hominin relatives) spread farther and faster than anthropologists have previously given them credit for.

“We never imagined anything like this for this area, but in hindsight, it’s not actually a very surprising result,” said Harvati. Evidence of Homo sapiens in Israel dates to at least 177,000 years ago, and southeastern Europe was probably an important route from the Levant into Europe and parts of Asia. “It’s not actually so unimaginable that some of these populations would have expanded their range to reach southeast Europe,” said Harvati.

Let the scientific debate begin

Harvati and her colleagues CT scanned the bone so they could digitally reconstruct the broken, distorted pieces of skull, then performed statistical analysis of how its dimensions and shape compared to other fossil skulls from humans, Neanderthals, and even older hominins. Consistently, the analysis suggested that Apidima 1 was human.

But that’s not to say there won’t be some debate, especially about the fossil’s age. Most calcium carbonate rocks, minerals that precipitate out of flowing water, also contain some uranium. By looking at the ratios of uranium isotopes in a rock or fossil, geochemists can date when it formed. In this case, Harvati and her colleagues came up with several potential dates, some of which are much earlier than 210,000 years ago. Geochemist Rainer Grün of Griffith University says that those earlier dates are probably the product of uranium from the breccia deposit—where the partial skull ended up after being washed through the cave sometime after death—leaching into the fossil bone over time.

It’s pretty common for paleoanthropologists to re-analyze, re-date, and argue about fossils, especially when they’re the centerpiece of a superlative claim like this one. Although Apidima 1 isn’t that much older than Misliya-1, it’s the oldest Homo sapiens fossil in Europe by a margin of about 150,000 years, and that’s a significant claim. It’s probably reasonable to expect to hear more about Apidima 1 in the future, one way or another.

A long, complicated relationship

“It’s a fantastic coincidence that you have two skulls together, 30cm (11.8 inches) apart,” said Grün. “In all of Greece, you have one more skull—that’s it—in that timeframe. It’s a wonder of nature that you find the two together.” The human and the Neanderthal probably died around 40,000 years apart, in different places in the labyrinthine Apidima cave system. At some point, water flowing through the cave washed both skulls down into the same chamber. The uranium isotope ratios in Apidima 1 were different from the surrounding rock, suggesting that they started out in different places and formed at different times. The Neanderthal’s signature, meanwhile, was more similar to the surrounding breccia.

The result may offer an uncanny fossil snapshot of our complicated history with the Neanderthals. Genetic studies of Neanderthal DNA have suggested that those living in Europe sometime after 270,000 years ago met early waves of human migrants. Those encounters left traces of human alleles in Neanderthal genomes, in the same way that Neanderthals, in turn, left traces in our modern genomes. Harvati says that Apidima 1 may be part of that long-lost group of humans who mingled with Neanderthals and then, apparently, disappeared.

Genetic evidence suggests that non-African populations today all descend from the wave of humans who dispersed into the rest of the world between 70,000 and 50,000 years ago. Older waves of dispersal, humans who left tools and bones at sites like Misliya, Qafzeh, and Skhul Caves in Israel, seem to have faded away without leaving descendants behind. And at several of those sites in Israel, the fossil record contains Homo sapiens remains in earlier layers, followed by Neanderthals in later ones. That suggests that somehow, Neanderthals temporarily replaced humans living in the area. Something similar likely happened to the first wave (or waves) of humans in Europe, as well.

“I would suspect that these were relatively small populations that made it all the way to Greece—for example, probably smaller than the source population in Israel, and of course ultimately from Africa,” said Harvati. Smaller groups would have been more vulnerable to local extinction. The first Homo sapiens may have arrived in the Levant and Europe to find Neanderthals already living there, and they co-existed for awhile before somehow dying out. Or perhaps the humans moved into unoccupied territory, only to later be edged out or absorbed by groups of Neanderthals migrating into the same region.

More questions to answer

But for now, paleoanthropologists don’t know exactly what transpired between the two species, or why—just as they don’t know exactly why the Neanderthals went extinct around 40,000 years ago. They need more evidence to tackle those questions and to understand exactly when, where, and why our species began to explore the world outside Africa. That means looking for more fossils, of course, but it also means prying more information out of the fossil record that’s already sitting in museums and university collections.

“I think the questions that will be asked now are what caused this early dispersal? What enabled it in terms of land bridges or particular routes of dispersal? Were there any technological advances that enabled such a far geographic intrusion into Europe?” said Harvati. “And also why did they die out?”

Harvati and her colleagues plan to try to find ancient DNA and proteins in the skulls from Apidima Cave, though she admits she’s not optimistic because the fossils are so old and the site is in such a warm region. Heat seldom bodes well for DNA preservation.

Meanwhile, Greece, like much of southeastern Europe, hasn’t exactly been a hotspot for paleoanthropology—despite its geographic importance. That’s mostly because archaeology in the region has been more focused on much later periods of human history. Paleoanthropology has started to get more attention in recent years, though, and that may eventually yield more finds like Apidima 1.

“We did not suspect this, so it’s possible that we will find [early human fossils] also elsewhere. It’s possible that they reached further than we thought before,” said Harvati. We can only answer this by finding more evidence.”

Nature, 2019. DOI: 10.1038/s41586-019-1376-z. (About DOIs).

https://arstechnica.com/?p=1533711