Jebel Irhoud rose to prominence in 1961, when miners turned the site into a quarry. They were looking for barite minerals, but to their surprise, they found a fossilized skull. Soon, they disinterred more bones: another skull, a child’s jaw, and fragments of arm bones and hips. From the start, these specimens were controversial. Their exact location was never recorded, which makes it very hard to work out their age. Scientists initially thought that they were the 40,000-year-old remains of Neanderthals—and were wrong on both counts. They’re much older, and they’re more likely to be Homo sapiens.

After those discoveries, Jebel Irhoud was neglected. But in 2004, Jean-Jacques Hublin from the Max Planck Institute for Evolutionary Anthropology led a team back to the site, clearing away decades’ worth of accumulated debris in a search for more fossils. And after a few seasons of digging, they found some—a partial skull, fragments of facial bones, a nearly complete adult jawbone, and other bits and pieces from at least five individuals.

These people had very similar faces to today’s humans, albeit with slightly more prominent brows. But the backs of their heads were very different. Our skulls are rounded globes, but theirs were lower on the top and longer at the back. If you saw them face on, they could pass for a modern human. But they turned around, you’d be looking at a skull that’s closer to extinct hominids like Homo erectus. “Today, you wouldn’t be able to find anyone with a braincase that shape,” says Gunz.

Comparison of the skulls of a Jebel Irhoud human (lleft) and a modern human (right) (NHM London)

Their brains, though already as large as ours, must also have been shaped differently. It seems that the size of the human brain had already been finalized 300,000 years ago, but its structure—and perhaps its abilities—were fine-tuned over the subsequent millennia of evolution.

At Jebel Irhoud, the team also found several stone tools—small pieces of flint with sharp edges. Several of these had clearly been heated in the distant past, but not because their makers were deliberately burning the implements. More likely, “you can imagine that people were dropping stones on the ground, and later starting fires on top,” explains Shannon McPherron, an expert on stone tools who was involved in the new study.

The team exploited this incidental heating to date the tools. Over time, flint gradually builds up a small charge as it reacts to natural sources of radiation around it. That charge dissipates whenever it’s heated, before growing again. By testing the stones back in their lab, McPherron’s team could work out how much charge they had accumulated since they were last heated—which must have been when they were dropped in the caves. This technique, known as thermoluminescence, told them that the tools were roughly 280,000 and 350,000 years old.

Some of the Middle Stone Age stone tools from Jebel Irhoud (Mohammed Kamal / MPI EVA Leipzig)

The team checked those dates by estimating the ages of the fossils. They first did that a decade ago, using the fossils collected in the 1960s, and they arrived at an age of 160,000 years. But that was based on imperfect guesses about the sediments in which the bones had been buried. This time, after taking careful readings from the site itself, the team could more accurately re-do their calculations. They got a much older date of 286,000 years, which matches well to the estimated age of the tools. “I think it’s a pretty tight picture,” says McPherron.