Of MYTH and MAN: our shifting story
HUMAN ORIGIN NARRATIVE EVER CHANGING
The origin story of humanity is changing. Evidence arrives slowly, and can take decades to be realized. But it keeps on coming. Often it is first found by a miner, and kept as a souvenir, such as a human skull in a Moroccan mine site, discovered half a century ago and proven this summer to be nearly twice as old as earlier estimates of the entire human species. Or it is found by a spelunker, for example the “Pit of Bones” cave in Spain, where the remains of two dozen individuals seem to be ancestors of Neanderthals, an extinct human species.
Sometimes t he evidence is macabre, like the human child’s skull, ceremonially polished and stripped of flesh, in a dusty Ethiopian valley. Other times it is simply curious, like the collection of stone hatchets in Madjedebe near Darwin in Australia, dated this summer to many millennia before humans were thought to have arrived there.
With each find, the traditional account of human origins is being revealed not as false, but as too simple. Horizons are being pushed back faster than textbooks can keep up. With guidance from genetics and fossils, even biomechanics, paleoanthropologists can now prove the human species is older than ever before; that it did not leave Africa once and definitively, but many times; that it comes from a far larger geography than is commonly imagined; and that it neither exterminated nor absorbed its contemporary cousins, the Neanderthals and the mysterious Denisovans, which rather died out all by themselves, just like every other hominin population that ever lived, except us.
“The common myth that we drove them to extinction is just that, it’s a myth,” said David Begun, a paleoanthropologist at the University of Toronto and author of The Real Planet Of The Apes: A New Story of Human Origins. It is not the only one. The textbook story is of a small population of Homo sapiens, perhaps as small as a few hundred, who became anatomically modern in a fertile corner of East Africa around 200,000 years ago. They were descendants of an ape that shares a common ancestor with chimpanzees, and although they would have had a sort of culture in the way other apes do, they only became behaviourally modern in the last 100,000 years, when they started to colonize the rest of Africa, then the Middle East, Europe and Asia, and eventually North and South America.
As they did, early humans started to leave behind evidence of conceptual t hought and shared language, both in the increasingly consistent fossil record of manufactured tools, and in the art that progressed swiftly, in just a few millennia, from the 75,000- year- old symbolic notches on bone tools and delicate seashell beads found in Blombos Cave, in a cliff face on a wild stretch of South Africa’s In- dian Ocean coastline, to the firelit grandeur of the 17,000- yearold cave paintings of Lascaux in France’s Dordogne.
This story is why, in pop science, the savannah of the Great Rift Valley has taken on the air of an evolutionary cradle, the place imagined in the atavistic fantasies of modern hunter- gatherers with liberal arts educations, where a lion lurks behind every bush on a genetic safari. This small corner of Africa, the story goes, was where the human mind and body were first shaped by the famous “four Fs” of evolution: fighting, fleeing, feeding and mating.
As a cartoon, the story is as familiar as The Flintstones. As a creation myth, it rivals the Garden of Eden. The trouble is that it is not quite true.
One reason the East African aspect of human origin theory caught on so firmly in the popular imagination was that it is the extreme opposite of another scientific hypothesis, the multiregional theory, that has been slowly rejected by evidence. It suggested that modern humanity was the end point of evolutionary processes that happened over the last two million years in many different archaic human populations all over Africa, Europe and Asia.
This theory has been pushed to the margins, however, by recent studies that show, for example, how long ago the human and Neanderthal evolutionary lines diverged ( 500,000 years) and how little Neanderthal DNA remains in the human genetic code (less than five per cent).
Another reason is that biology, at this level, can have political overtones and, as compared with the multiregional theory, the view that modern humans share an especially small set of East African ancestors — that everyone is literally part of the same family, even sharing a theoretical grandmother known as Mitochondrial Eve — can be politically attractive. For one thing, it seemed to neatly eliminate race as an evolutionary category. It was a clear reminder that Homo sapiens has no subspecies. Caucasians did not sprout spontaneously in the Caucasus. Asians did not originate in Asia. Everybody came from East Africa. Even Donald Trump is Kenyan.
Recent discoveries are challenging the tidiness of this origin story.
As science writer Gemma Tarlach put it in Discover Magazine, “the conventional timeline of human evolution and migration continues to crumble in the face of new research.”
One major theme is that humanity keeps looking ever older. And while the African origin remains certain, it has changed dramatically in scope.
This was the astonishing significance of the Moroccan discovery, reported in Nature in June. For decades, these bones, from a site called Jebel Irhoud, were thought to be Neanderthals. But as more bones were discovered, their human features were recognized, and as scientific dating techniques improved, the sedimentary layer that some were found in was shown to be as many as 350,000 years old.
As l ead researcher Jean-Jacques Hublin described it, the presence of anatomically modern Homo sapiens in Morocco that long ago is hard to resolve with the traditional story. It seems to show that the evolutionary Garden of Eden was not some specific East African grassland. It was probably more like the entire continent of Africa, a full fifth of Earth’s land area. And most of those human populations simply died out.
“The fact that ( the Jebel Irhoud bones) date to that time pretty much excludes them as a potential ancestor of anyone l i ving today,” said Matthew Tocheri, an anthropologist and Canada Research Chair in Human Origins at Lakehead University, now on a posting to the University of Kent. “That’s just because of the way that the differences can accrue over time between the genetic lineage and the species, right? You’re always going to have individuals and populations within a species that go extinct and leave no living descendants.
“So they represent basically lost lineages of people leaving Africa, and their descendants slowly expanding into parts of Europe and Asia, but then for whatever reason, those populations went extinct. And subsequently, somewhere around 50 to 70,000 years ago, we have groups of modern humans beginning to leave Africa again, and they’re essentially the ancestors of all of us that are of non- African descent,” Tocheri said.
There are similar finds in Europe, he said, more recent, but with genetic combinations that no longer exist in humans. So there is a pattern of ancient humans leaving Africa, becoming isolated, and eventually going extinct, but leaving a distinct fossil record. The famous “hobbits” whose remains were discovered in 2003 on the Island of Flores in Indonesia, known as Homo Floresiensis, are a good example, said Tocheri. If anthropologists found such bones in Africa and dated them to around three million years ago, it would have been no big deal, he said. But finding them in Indonesia, at a time that overlapped with modern humans, as little as a few thousand years ago, “all of a sudden you’ve got a problem,” Tocheri said.
“The context of that find really challenged people’s thinking, but now, 15 years later, it’s not as challenging, because we really see this process of dispersal happening again and again for the past two million years,” Tocheri said.
“So likely Homo Floresiensis represents descendants of some of those earliest dispersals of humans out of Africa, long before even the common ancestor of humans and Neanderthals evolved and left Africa.”
The story is much the same with Neanderthals, who are well known from European sites especially, and Denisovans, of whom science knows barely anything other than that they once existed in Asia.
The traditional way to describe the fate of Neanderthals is as a debate between extermination, in which the cleverer Homo sapiens was able to conquer this competitor, and absorption, in which the two populations merged through procreation, such that eventually there were no more Neanderthals left.
But neither side of that debate really stands up.
“There’s no evidence at all in the archeological or fossil record of modern humans interacting with Neanderthals” said Begun, of the University of Toronto.
There is genetic evidence of interbreeding however, especially of Denisovans with Homo sapiens in Asia. But as the pioneering paleogeneticist Svante Paabo has described it, that genetic interplay never really caught on.
Tocheri, likewise, says there is good data that shows Neanderthals interbred with Homo sapiens, but the signal of Neanderthal in modern non- African human DNA, for example, is “rather small, and there have been clear selective sweeps against Neanderthal DNA in our DNA. So what that means is essentially it wasn’t really as compatible as any other two populations of modern humans breeding together.”
Within Africa, modern Homo sapiens seem to have been pretty much everywhere at the earliest stages. Many populations went extinct, some migrated out, some might even have migrated back. Begun thinks there might be fossil remains of human populations in Europe or Asia even as old as the Jebel Irhoud population. But only one managed to survive to the present day, thanks to a combination of farming and luck.
“There is no way to know from what part of that population the first modern humans did so (left Africa),” said Begun.
This fateful migration out of Africa was just one of many, and it did not involve any known increase in cognitive power or physical strength or dexterity or technological sophistication, Begun said. Fire had been controlled for millennia.
Humanity’s ancestors had been making stone tools in a standardized fashion for well over a million years. There was no new technology. It was probably just wandering.
Modern geography is as important to this question as ancient. For one thing, the Sahara Desert did not exist at the relevant times, so it was no barrier. Also, East Africa today is just a good place to find old bones, and to date them.
There are plenty of badlands, dry and free of obscuring vegetation. The Great Rift Valley deposits volcanic ash in predictable layers. Dating is easier than elsewhere. As Begun put it, looking for ancient humans in East Africa is like the proverbial drunk looking for his keys under the street light — because he can see better there.
This is just one reason for the persistent inaccuracies as humans have tried to string together a bunch of dusty bones and stones into their own origin story.
SOMEWHERE AROUND 50 TO 70,000 YEARS AGO, WE HAVE GROUPS OF MODERN HUMANS BEGINNING TO LEAVE AFRICA AGAIN, AND THEY’RE ESSENTIALLY THE ANCESTORS OF ALL OF US THAT ARE OF NON-AFRICAN DESCENT. — MATTHEW TOCHERI, ANTHROPOLOGIST TIMELINE OF EVOLUTION CONTINUES TO CRUMBLE IN THE FACE OF NEW RESEARCH.