Our species may be 150,000 years older than we thought

Has our species been hiding its real age? Fossils found in Morocco suggest the Homo sapiens lineage became distinct as early as 350,000 years ago – adding as much as 150,000 years to our species’ history.

“It was indeed a big wow [moment],” says Jean-Jacques Hublin at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the analysis with Abdelouahed Ben-Ncer at the National Institute of Archaeology and Heritage in Rabat, Morocco.

On a literal reading of the fossil record, H. sapiens was thought to have emerged in East Africa roughly 200,000 years ago. But some researchers have long suspected that the roots of our species are deeper, given that H. sapiens-like fossils in South Africa have been tentatively dated at 260,000 years old.

The new evidence provides solid support to those suspicions. It comes from a Moroccan site called Jebel Irhoud (pictured below), which has been puzzling human evolution researchers for more than 50 years.

Hominin remains were found at the site in the 1960s. They have such an odd mix of ancient and modern features that they were initially mistaken for an African version of Neanderthals. Later reassessments put them closer to our species, and about a decade ago a dating technique suggested they were about 160,000 years old.

But by that point in prehistory, it is conventionally assumed that our fully modern species were already living in Africa, which made the Jebel Irhoud hominins’ mix of ancient and modern features confusing.

So Hublin and Ben-Ncer’s team returned to Jebel Irhoud to try to solve the puzzle. In fresh excavations, they found stone tools and more fragmentary hominin remains, including pieces from an adult skull.

An analysis of the new fossils, and of those found at the site in the 1960s, confirms that the hominins had a primitive, elongated braincase. But the new adult skull shows that the hominins combined this ancient feature with a small, lightly built “modern” face – one that the researchers say is virtually indistinguishable from H. sapiens.

But what about the confusing date? In a complementary study, Shannon McPherron, also at the Max Planck Institute for Evolutionary Anthropology, and his team took a closer look at the stone tools. Many of them had been baked, he says – probably because they were discarded after use and then heated when the hominins set fires on the ground nearby.

This heating “resets” the tools’ response to natural radiation in the environment. By assessing the levels of radiation at the site and measuring the radiation response in the tools, McPherron and his colleagues established that the tools were heated between 280,000 and 350,000 years ago. McPherron’s team also re-dated one of the hominin fossils found in the 1960s using their insight into the radiation levels at Jebel Irhoud and concluded it is 250,000 to 320,000 years old.

Armed with these dates, the Moroccan hominins become easier to understand, says Hublin. The researchers suggest that H. sapiens had begun to emerge – literally face-first – between about 250,000 and 350,000 years ago. Although other features of their anatomy still looked primitive, the Jebel Irhoud hominins should be considered the earliest known members of our species, say Hublin and his colleagues.

Not everyone is convinced, however. “There is a bit of a redefinition of what a modern human is here,” says Lee Berger at the University of the Witwatersrand in Johannesburg, South Africa.

Modern-looking face

“The face is modern looking,” says Juan Luis Arsuaga at the Complutense University of Madrid, Spain. “But the mandible [jawbone] is not clearly modern. I would say that Jebel Irhoud is not yet H. sapiens, but I would bet that H. sapiens evolved from something very similar to Jebel Irhoud.”

However, Chris Stringer at the Natural History Museum in London is willing to loosen the definition of H. sapiens. He says he would once have restricted the name to “anatomically modern humans” – those with the full set of features we see in living people. “Now, I think that anatomically modern humans are only a sub-group within the species H. sapiens,” he says. We should consider including the Moroccan hominins in our species even though some of their features look ancient, he says.

Stringer thinks we shouldn’t be surprised to discover that our species is far more ancient than once thought. We know that our lineage split from the Neanderthal lineage at some point in prehistory, with Neanderthals then evolving in Europe while H. sapiens evolved in Africa. Recently, fossil and genetic evidence has suggested that this split occurred at least 500,000 years ago. “In my view, the date of this divergence should mark the origin of these two groups,” says Stringer.

This would imply that, roughly 500,000 years ago, Neanderthal-like hominins began appearing in Europe and H. sapiens-like hominins began appearing in Africa. In keeping with this idea, 430,000-year-old hominins found at a site called Sima de los Huesos in Spain do seem to be Neanderthal-like. Jebel Irhoud could be seen as the African, H. sapiens equivalent of Sima de los Huesos, says Stringer.

Well-dated fossils

Aida Gómez-Robles at University College London agrees with this way of thinking. “I would predict that we will find in the future even older transitional forms for both Neanderthals and modern humans,” she says.

But although the Jebel Irhoud fossils suggest H. sapiens had evolved a modern face 350,000 years ago, working out how, where and when our species evolved its other modern features will be challenging. “We have so few well-dated fossils,” says McPherron.

Adding to the challenge, says Berger, is that we know H. sapiens wasn’t the only hominin in Africa at the time. Earlier this year, he and his colleagues confirmed that an unusually small-brained human – Homo naledi – found in the Dinaledi chamber of South Africa’s Rising Star cave was alive between 236,000 and 335,000 years ago. “It’s amazing that Jebel Irhoud and Dinaledi exactly overlap. That’s fantastic,” he says, adding that the two are essentially the only securely dated African hominins known from this time period.

As such, Berger thinks any conversation about the spread and rise to dominance in Africa of H. sapiens has to make reference to H. naledi.

“I’m disappointed that they didn’t include H. naledi in their discussions,” he says. “We just don’t know the relationship between these two hominins – they might even have interbred. H. naledi has to be relevant to the debate.”

References: Nature, DOI: 10.1038/nature22335 and DOI: 10.1038/nature22336