Is The Story Of Human Evolution Undergoing A Major Rewrite?

(Vox) The story of human evolution in Africa is undergoing a major rewrite

Updated by Brian Jun 7, 2017, 1:00pm EDT

Did scientists discover the oldest Homo sapiens remains on record? Depends on your definition of what’s human.

There’s a story that we’ve been telling about the origin of our species. It goes something like this: Around 200,000 years ago, in East Africa — near modern-day Ethiopia — the first Homo sapiens diverged from an ancestral species, perhaps Homo erectus. From there, we spread, in a linear manner over millennia north into Europe, and then through the rest of the world.

That story, it turns out, is wrong — or at least woefully incomplete. In two papers published in Nature Wednesday, anthropologists say they’ve found evidence that the dawn of our species may have actually been much earlier.

Their evidence is remains of human ancestors, dating at around 300,000 years old, that look a lot like Homo sapiens and were found in the Jebel Irhoud cave in Morocco — thousands of miles from Ethiopia.

That’s significant because it’s “much older than anything else in Africa we could relate to our species,” Jean-Jacques Hublin, the director of human evolution at the Max Planck Institute for Evolutionary Anthropology and a lead author on one of the papers, said. “This represents the very root of our species, the oldest Homo sapiens ever found in Africa or elsewhere.”

Or maybe not. Whether these remains truly represent the “root” of humanity depends on what your definition of what humanity is. And on that question, there’s surprising nuance and disagreement.

An anthropological oddity that could be the oldest Homo sapiens skull ever found

These specimens — pieces of skull, jaw, and assorted other body parts of five individuals — are not new to paleoanthropology.

The first pieces of them were discovered in the 1960s by miners clearing a hillside in Morocco. And they were a curiosity. Scientists at the time assumed the fossilized remains — along with fragments of their stone tools — relatively new, maybe only 40,000 years old.

But something didn’t add up: The specimens looked more primitive than what you’d find from 40,000 years ago. Their facial structures looked modern, but parts of the skull that surround the brain were smaller in some key areas.

When the authors of the Nature paper got the chance to reanalyze the site in recent years, they gathered fragments of flint that had been exposed to fires made by the occupants.

The dating technique they used is called thermoluminescence. And it’s pretty cool.

When those early humans put their flint tools into the fire all those millennia ago, the heat released electrons from the rock’s crystalline structure. Since, those electrons have beenslowly replenished over time from solar radiation. In the modern day, scientists heat up those pieces of flint, and the reaccumulated electrons are released, measured, and can give scientists a date for when they were initially fired. That’s how they got 300,000 years (give or take a few tens of thousands of years).

Hublin says these individuals were not “modern humans” like us, but a slightly earlier form of Homo sapiens, one with a less developed brain and perhaps other differences in its DNA. And he says these differences between us and them are proof that evolution occurs over a gradient. It also shows the biggest evolutionary change we’ve undergone in the past 300,000 years is in the size of our brains.

And all this evidence, he says, points to a “pan-Africa” hypothesis of human development.

The hypothesis: No, we did not just emerge in Eastern Africa. As of 300,000 years ago, our ancestors were already spread around the continent (paleoanthropologists have identified a probable Homo sapiens skull in South Africa dating back 250,000 years).

And they were on the move, and spreading their genes. “The idea is that there is no [one] Garden of Eden in Africa, or if there is a Garden of Eden, it is Africa,” Hublin says.

But are they really Homo sapiens? Science doesn’t give an easy answer here.

I ran Hublin’s paper and conclusions by two other anthropologists — Ian Tattersall, the curator emeritus of human origins at the American Museum of Natural History, and John Hawks, a professor at the University of Wisconsin. And while they don’t doubt the dating of these findings, they do question whether we can really call these specimens Homo sapiens.

After all, they do have some significant differences with us when it comes to the shape of their brains, which is a defining characteristic of our kind.

“I think you have to be fairly rigorous [with] what you admit into Homo sapiens,” Tattersall says. “There are plenty of people out there who are willing to take a much looser view of what Homo sapiens is, and would be happy to cram this into Homo sapiens as a matter of convenience, or a matter of philosophy even. I wouldn’t go along with that.”

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