Late last month, we reported on how new fossil finds had changed what were thought to be settled questions about the last common ancestor between chimpanzees and humans. Now, we’ve got news of another major upset to the known human timeline and our own appearance on planet Earth.
Previously, the earliest fossil remains of anatomically modern humans (AMH) were found in Ethiopia and dated to ~200,000 years ago. Many other AMH fossils have been found in the same areas of Africa, and the scientific consensus has been that these finds represented the first appearance of modern humans. This single origin hypothesis isn’t the only theory for how humanity first emerged and then spread across the continent and planet, but it’s been the most common argument for a number of years. These new finds, located in Morocco, challenge the existing narrative. It was believed that humanity spread across Africa for over a hundred thousand years before traveling to new continents roughly 70,000 years ago.
This new work is from a site named Jebel Irhoud, where excavations have been ongoing for decades. Part of what sets them apart is that the research team isn’t working from just one skull or bone fragments from a single individual, but a group of five separate people. Dr. Hublin and his colleagues used a technique known as thermoluminescence, a technique that measures the accumulated radiation dose of objects that have previously been heated or exposed to sunlight to measure how old they are. The degree of luminescence is proportional to the radiation dose absorbed by the material in question.
In this case, the dating method established that flint blades buried at the site had been burned, probably through exposure to cooking fires, roughly 300,000 years ago. The skulls the expedition found were in the same rock layer as the flint blades, which strongly implies they date to roughly the same time period.
One of the interesting differences between early and modern humans (both of which are classified as homo sapiens sapiens) is that while they looked nearly identical to us, their brains were shaped differently. It’s proven difficult to find a comparison image of brain size, but this slide does show the subtle difference in skull shape between early and modern man.
Both our skulls and our brains have become rounder over the millennia, possibly driven by an enlarged parietal lobe and cerebellum compared with the earliest examples of modern humans. How and if this changed how humans think is unknown. The humans who lived at Jebel Irhoud could start fires and craft spears. The flint that they used for their weapon tips wasn’t local to the area, but came from a site some 20 miles south of Jebel Irhoud. This suggests that early humans knew how to find resources and utilize them even when said resources were scattered rather than grouped in a single location. That’s significant in and of itself, particularly for remains as unusual as these.
The argument advanced by Dr. Gunz and Dr. Hublin is that human beings didn’t evolve at a single location or even one specific place. “What we think is before 300,000 years ago, there was a dispersal of our species — or at least the most primitive version of our species — throughout Africa,” Hublin toldNature. Around this time, the Sahara was green and filled with lakes and rivers. Animals that roamed the East African savanna, including gazelles, wildebeest and lions, also lived near Jebel Irhoud, suggesting that these environments were once linked.”
So how do these finds, assuming they prove to be accurately dated and to belong to our own species, change our understanding of human evolution? They suggest, at minimum, that homo sapiens sapiens was around much earlier than we previously thought it was. Whether our species evolved in a single specific location or more generally across the continent is still unclear. And not every scientist agrees with Gunz and Hublin that the Jebel Irhoud bones are clear evidence for AMHs more than 100,000 years before they were previously thought to have emerged.