When did modern humans begin to evolve? And from who? Once upon a time it was thought that, OK, we began from a monkey but then there was a linear progression to the wonder that is we, starting about 200,000 years ago. It is now abundantly clear that we are mongrels, admixing merrily with other human species until they all died out, and now an early modern human previously found in Ethiopia has been redated with the help of a volcano to 233,000 years ago.
That is 36,000 years earlier than the date originally ascribed to the early Homo sapiens specimen found at the site Kibish Omo I, according to a new paper in Nature by volcanologist Prof. Céline Vidal of the University of Cambridge, Prof. Aurélien Mounier, a paleoanthropologist with the Museum of Mankind in Paris, and colleagues.
Originally found in the 1960s, the specimens in Omo had been dated to 197,000 years and another set of early modern humans found at another Ethiopian site, Herto, were dated to 160,000-155,000 years.
But as happens, the dates had been hotly disputed. Now, geochemical analysis of volcanic crud lying atop the ancient bones redates that site to about 233,000 years old, making Omo Person the earliest known specimen of Homo sapiens in Eastern Africa. Investigation into the age of the Herto humans is still in progress.
The age of Man
Why actually does the age of the earliest modern humans in Ethiopia matter?
To be sure, there are claims of even older Homo sapiens specimens elsewhere in Africa – the most striking being one dated to about 300,000 years ago in Jebel Irhoud, Morocco. Beyond Africa, a modern human jaw was also reported from Misliya Cave, northern Israel, dating to about 200,000 years ago.
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But the claims that these represent early anatomically modern humans are controversial.
Mounier for one is doubtful, especially about the remains at Jebel Irhoud. “The specimen lacks most of the specific morphological characters of H. sapiens,” he says. Our cranial vault is tall and globular and we have a chin, which the Irhoud person does not, he explains.
What about Misliya Mandible Person? “Misliya is a bit different,” he answers. First of all, it is considerably younger than the Irhoud person, and it is also younger than the new date estimates for the Omo specimen. “It seems to me that what makes Misliya modern is mostly the shape of the maxilla and the presence of a canine fossa. … This is interesting, because this is also what makes Irhoud 1 modern: the shape of the maxilla, the presence of a canine fossa. Nevertheless, the morphology of the rest of the skull is not modern. I am not saying that Misliya does not represent a Homo sapiens, and I would not be surprised if modern humans would have reached the Near East just after 200,000 years ago, given that they are present in East Africa around 230,000 years ago.”
The specimens in Omo and Herto do have the modern morphologies regarding chin and tall cranial vault, the team spells out. “In my opinion, Omo 1 is the oldest unchallenged fully modern specimen, the oldest Homo sapiens as we morphologically define the species nowadays,” Mounier says. “This is why this new dates are important. They may not tell us much about how modern humans evolved, but they tell us that before 200,000-230,000 years ago, hominins that are by our current standard recognizable as Homo sapiens, were already present in Eastern Africa.”
As the team writes: shifting the age of the oldest known Homo sapiens fossil in Eastern Africa is consistent with separate evidence that the modern human lineage is older than had been thought, the team writes.
The East African paradigm
Another almost consensual idea under attack is that H. sapiens arose from a unique East African population, which emerged around 200,000 years ago. The notion of age and origin are challenged by the results of a very new technology: analysis of ancient DNA.
New results in genomics place the genetic divergence of H. sapiens at around 300,000 years ago, Mounier explains – and there have also been some impressive paleoanthropological discoveries which presented possible “archaic” H. sapiens that are older than 200,000 years elsewhere in Africa, and even elsewhere.
“I think a new consensus is slowly emerging in the field that acknowledges the complexity of the evolutionary processes which gave birth to our species. Indeed, it seems likely that H. sapiens emerged in Africa from the interaction and admixture of different ‘archaic’ populations,” he says.
One recently suggested theory is that Homo sapiens evolved “all over Africa,” getting about and mixing and matching. Mounier qualifies that “looking at the current paleoanthropological and genomic evidence, it appears that it may have not been ‘all over Africa,’ and it could be that the process was more centered around eastern and southern Africa,” he says.
A volcano blows
Part of the reason for the mystery surrounding our origins is the paucity of fossils, as opposed to stone tools. Our tools litter the Old World, but in all of Africa – the continent of our species’ birth – only eight sites have yielded fossils of early Homo sapiens from the Late Middle Pleistocene, which spanned 350,000 years to 130,000 years ago. (To be clear, the eight are specimens believed to belong to Homo sapiens, as opposed to other hominins such as australopithecus.)
One problem bedeviling science is identifying species from fossils. In one recent rumpus, recently reported remains found in Israel were identified as Ramle Nesher Homo, a precursor to Neanderthals; others rebut that it was apparently just a Neanderthal. In 2021, a “new human species,” Dragon Man, was reported in China; others think it was a Denisovan or possibly just a Neanderthal.
Dating hominin fossils is also quite the knotty conundrum. But the team is confident that at Omo, and Herto, they have real, anatomically modern humans, early ones.
And now let us look at how they redated the Omo remains from 197,000 to 233,000 years ago.
Omo had been dated based on layers of ash corresponding to the timing of volcanic eruptions, but the original determination was challenged, Vidal, the volcanologist, explains. There is a layer of volcanic ash above the Omo bones – which means the eruption was after the Omo person died. But that particular layer couldn’t be directly dated because the ash is very fine, like powder, which isn’t suitable for the classic technique of dating ash layers, she says. Why? Never mind. We shall accept that and move on.
“When we can’t directly date a volcanic ash layer, Plan B is to identify the chemical signature of the ash, which relies on every eruption having its own chemical fingerprint – that’s a fantastic tool,” she says.
Yes, every eruption has its own chemical signature – even eruptions from the same volcano.
“Once we have the chemical signature of one eruption, we can compare with other ash layers from other places: we have to be confident in the date and chemical composition of the ash!” she says.
Which begs the question, how did they find certain correlation? She explains that the raison d’être of this Omo-Herto project, among other things, was to characterize the timing and chemical signature of all the colossal eruptions in Ethiopia between 300,000 to 60,000 years ago, a time when our ancestors were living in the rift valley of Ethiopia, and see how these linked to human evolution in general and to human migrations.
So they deduced the timing and chemical fingerprint of all the catastrophic eruptions there, and compared these eruption fingerprint with the ash layers from Omo. And voilà, they discovered that the specific ash lying above the Omo human was produced when a volcano named Shala blew its top 233,000 years ago.
So, QED, the bones in Omo have to be older than 233,000, she explains.
OK, and what about ash below the Omo bones, which would help us narrow the range in time? How old is that? “That would be the next step,” she confirms. “There is an ash layer below which we are working on. It’s a very difficult place to access,” she adds.
In short, more work needs doing to determine Omo’s range, and the somewhat younger humans in Herto as well, who nestle beneath a completely different volcanic ash layer than their cousins at Omo.
The bottom line is that the new dating for Omo Person fits with new models of modern human evolution that suggest our species diverged from our closest hominin ancestors around 350,000 to 200,000 years ago, Mounier says.
Meanwhile, completely unrelated work suggests that modern human populations in Africa diverged around 300,000 years ago – which makes sense if you think about the geography, vagaries of climate, and so on. It’s just a rather shocking thought to the modern mind, accustomed to thinking of a five-generation family tree as being somehow impressive.
Asked what he thinks about that theory, Mounier responds that it’s “interesting because the new date estimates for Omo 1 bring it closer to that time frame, which also mean that we should start seeing Homo sapiens fossils in the fossil record from that time.”
And it bears keeping in mind that our divergence within our species may have begun then, but we Homo line persons have incredible wanderlust and we can assume that even populations who separated hundreds of thousands of years ago subsequently met anew, and mixed.