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

Theres a story that weve 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 theyve 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.

Thats significant because its 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, theres surprising nuance and disagreement.

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 didnt add up: The specimens looked more primitive than what youd 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 its pretty cool.

When those early humans put their flint tools into the fire all those millennia ago, the heat released electrons from the rocks crystalline structure. Since, those electrons have been slowly 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. Thats 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 weve 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.

I ran Hublins 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 dont 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 wouldnt go along with that.

Hublin is firm in his belief that these are indeed Homo sapiens. Evolution exists, he responds. The reality is that there is a continuous line of evolution between early sapiens like Irhoud and humans of today without any breaking point along this line.

I do think theres a really interesting story here, but we dont quite know what it is

Evolution is not a straight line. Its one that produces many branches (most of which die off). Those branches can also join back together in the future. Those rejoined branches sprout branches. Some of those branch off and recombine. Others die. Its a tangled mess.

The lineages are constantly splitting, dying, and rejoining. Its believed our line split off from our closest relatives, the Neanderthals, around 500,000 years ago. But its not clear when we became human. Evolution doesnt always provide clean cutoffs from one form of a species to the next.

Are these Moroccan specimens truly our ancestors? We cant know. Did they give rise to our ancestors who lived in East Africa? Maybe. Or are they an offshoot of the main line, a group that was on their way to becoming their own distinct species but then died off? Also possible.

As long we have properly identified the actors in the play, were not going to understand the plot, Tattersall says. I do think theres a really interesting story here, but we dont quite know what it is.

At the very least, Tattersall says this evidence pushes back the start date of the middle Stone Age the age when people started to make sharp blades out of stone.

That we dont know how human these people were makes me appreciate the complexities of evolution a bit more.

Hawks says to imagine youre holding your mothers hand, your mother is holding her mothers hand, and the chain continues all the way back 300,000 years. What were talking about is about 10,000 to 15,000 [people] in a row the population of a small town is what connects you to that time frame, he says.

Youre connected to the person at end of the chain, yet they dont look quite like you. Their face is the same, but their skull is a little smaller. Maybe they have a harder time keeping up with the fast pace of your conversation. That person is both like you and something different at the same time.

The fossil record isnt this neat, however. I cant connect the dots yet, Hawks says. There are too few dots. Just too few. We dont have all the links in the chain from our mothers now to our mothers 300,000 years ago.

What is true: Each year, our human story grows more complicated and fascinating. Just in the past decade weve learned, through DNA evidence, that we mated with Neanderthals, Denisovans, and probably several other species of the genus Homo. Weve learned that at one time our world was inhabited by several subspecies of human. And we interacted with them.

Still, theres so much we dont know. And meanwhile, we keep making startling new discoveries: like the short-bodied Homo naledi that lived around 250,000 years ago and could have been in contact with our ancestors. Our experience in Stone Age Africa however it went wasnt simple.

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