Where and when did our species appear? At least 300,000 years ago, and probably in different points on the African continent, suggest the most recent discoveries... which sign the end of a long accepted theory:that of a single and localized focus.
A Homo sapiens draws animals on the wall of a cave (cave painting).
This article is taken from n°204 of Indispensables de Sciences et Avenir, dated January/March 2021.
In 2017, Homo sapiens has taken on a nice old look with the discovery of bones over 300,000 years old. A leap in time that could well revolutionize our prehistory textbooks… Because these remains are 100,000 years older than the age hitherto accepted for our ancestor. Better ! These remains were found not in East or South Africa, regions that until recently disputed the title of the cradle of Sapiens, but in Djebel Irhoud, Morocco. Some had already been known since the 1960s. Those responsible for this new excavation campaign, Jean-Jacques Hublin, director of the human evolution department at the Max-Planck Institute in Leipzig and professor at the the paleoanthropologist Abdelouahed Ben-Ncer, professor at the National Institute of Archeology and Heritage Sciences in Rabat, Morocco, however had the intuition that the site still harbored surprises… An intuition magnificently confirmed! Sixteen new fossils have been discovered, and thermoluminescence dating has made it possible to forget the age of 40,000 years announced in the 1960s according to carbon-14 dating. The particularity of these fossils is to present both characteristics say modern like a flattened face specific to Homo sapiens , and others more archaic, notably a less globular skull than later Sapiens. "I don't know if the few individuals discovered at Djebel Irhoud had any descendants , says Jean-Jacques Hublin. But it is undeniably a group anatomically very close to our ancestors." Djebel Irhoud, cradle of Sapiens? Not so sure…
Until the 1990s, paleontologists could still defend the idea of an emergence of multiple and ancient Sapiens:according to this so-called multiregionalist hypothesis, modern populations would be directly descended from local archaic groups rooted for hundreds of thousands of years. in Africa, Asia and Europe, themselves descended from human species, such as Homo erectus , which emerged from Africa as early as 2 million years ago. "This hypothesis is part of a very old historical tradition. It echoes the polygenist theses of the 18th century (modern humans would be the descendants of as many Adam and Eve as there are continents, editor's note), explains Jean-Jacques Hublin. At the beginning of the 20th century, we went so far as to falsify paleoanthropological data to accredit it, for example with the fossils of Piltdown Man." The bones in question, "discovered" in Great Britain, were presented as proof of the existence in Europe of the missing link between humans and apes. It was actually... a modern human skull attached to an orangutan's mandible!
Time machine
This article is taken from n°204 of Indispensables de Sciences et Avenir, dated January/March 2021.
In 2017, Homo sapiens has taken on a nice old look with the discovery of bones over 300,000 years old. A leap in time that could well revolutionize our prehistory textbooks… Because these remains are 100,000 years older than the age hitherto accepted for our ancestor. Better ! These remains were found not in East or South Africa, regions that until recently disputed the title of the cradle of Sapiens, but in Djebel Irhoud, Morocco. Some had already been known since the 1960s. Those responsible for this new excavation campaign, Jean-Jacques Hublin, director of the human evolution department at the Max-Planck Institute in Leipzig and professor at the the paleoanthropologist Abdelouahed Ben-Ncer, professor at the National Institute of Archeology and Heritage Sciences in Rabat, Morocco, however had the intuition that the site still harbored surprises… An intuition magnificently confirmed! Sixteen new fossils have been discovered, and thermoluminescence dating has made it possible to forget the age of 40,000 years announced in the 1960s according to carbon-14 dating. The particularity of these fossils is to present both characteristics say modern like a flattened face specific to Homo sapiens , and others more archaic, notably a less globular skull than later Sapiens. "I don't know if the few individuals discovered at Djebel Irhoud had any descendants , says Jean-Jacques Hublin. But it is undeniably a group anatomically very close to our ancestors." Djebel Irhoud, cradle of Sapiens? Not so sure…
Until the 1990s, paleontologists could still defend the idea of an emergence of multiple and ancient Sapiens:according to this so-called multiregionalist hypothesis, modern populations would be directly descended from local archaic groups rooted for hundreds of thousands of years. in Africa, Asia and Europe, themselves descended from human species, such as Homo erectus , which emerged from Africa as early as 2 million years ago. "This hypothesis is part of a very old historical tradition. It echoes the polygenist theses of the 18th century (modern humans would be the descendants of as many Adam and Eve as there are continents, editor's note), explains Jean-Jacques Hublin. At the beginning of the 20th century, we went so far as to falsify paleoanthropological data to accredit it, for example with the fossils of Piltdown Man." The bones in question, "discovered" in Great Britain, were presented as proof of the existence in Europe of the missing link between humans and apes. It was actually... a modern human skull attached to an orangutan's mandible!
Time machine
A falsification impossible today. Because if the paleoanthropological data - essentially the anatomy of the bones - can be subject to controversy when dealing with ancient human remains, a tool that appeared about thirty years ago makes it possible to decide with almost absolute certainty:the genetic analysis. Admittedly, ancient DNA requires almost perfect preservation conditions, and many bones are too damaged to be able to teach us anything. But DNA analysis is not limited to fossils. Contemporary genomes remember the dynamics of past populations, like a time machine kept in each of us. "Since the 1990s, genetic data has allowed us to confirm that Sapiens is indeed from Africa , notes Étienne Patin, CNRS researcher in the human evolutionary genetics laboratory at the Pasteur Institute. The analysis of contemporary genomes shows that genetic diversity outside Africa is lower than within the continent:which confirms that all non-African human groups form a single branch on the tree of Homo sapiens. All the others are represented by African groups. The trunk of the tree is therefore very African." Genetically, there are more differences between two African groups than there can be between, say, Europeans and Polynesians.
Homo Naledi , a much smaller distant cousin
If there is consensus on Sapiens the African, the debate is not yet closed. The challenge now is to know more precisely where and when our species was born. "Three main hypotheses are defended, explains Paul Verdu, researcher at the CNRS. That of a small group that would have won over all the others. In other words, a unique Sapiens home. The second proposes a bushy model:we must not look for our origin in a single group, but in several populations sometimes in contact, sometimes separated. The third theory is quite similar, except that it evokes more of a network:the different groups were intertwined and in constant exchange." Supporter of the first hypothesis, geneticist Vanessa Hayes, from the University of Sydney, announced in 2019 that she had discovered the home of humanity in northern Botswana. This work, published in the journal Nature but strongly criticized, mainly used the information provided by mitochondrial DNA, which is transmitted only by the mother. This scenario which, moreover, has not been confronted with archaeological data, remains fragmentary.
"Each indicator taken separately can tell its own story, warns Antoine Balzeau, paleoanthropologist at the National Museum of Natural History (MNHN). A story that may seem contradictory to that suggested by other indicators. Using mitochondrial DNA is an important bias, as is seeking to tell history solely from contemporary DNA. Rather than proving that there is only one home of humanity, this work has shown us that an extremely ancient human genetic lineage still exists (it is found for example among the Khoisan, in southern Africa, editor's note). A line that has contributed to the history of our ancestors, but like many others that are still unknown."
Whatever the theories, scientists agree to date the appearance of our species to around 300,000 years ago. "We know from genetics that the Khoisan are the descendants of the oldest group of Homo sapiens to have separated from the others more than 200,000 years ago , says Étienne Patin. Which means that we can trace the origin of our species beyond this period ."
To clarify this scenario, it may be useful to ask the question:but what did humanity look like in Africa when Sapiens appeared? "Anatomically very different groups were then able to live at similar periods, and even cohabit", says Antoine Balzeau. In South Africa, human remains discovered in 2013 identified a previously unknown group of hominins that lived around 300,000 years ago:Homo naledi , distant cousin of Sapiens, much smaller than him. Other fossils, discovered at Broken Hill (now Kabwe, Zambia) at the turn of the century, are attributed to Homo rhodesiensis , who himself lived between 700,000 and 300,000 years ago. "The dating of 300,000 years is particularly interesting because it marks a milestone for the most known African bands (Homo naledi, Homo ergaster, Homo rhodesiensis, editor's note) and the beginning for Homo sapiens", adds Jean-Jacques Hublin. At this pivotal time, very different groups will therefore gradually give way to this new species. A puzzle of humanities which remains however complicated to reconstruct. "We must succeed in understand evolutionary patterns from a very small number of clues, often separated from each other by tens or even hundreds of thousands of years", says Martin Friess, biological anthropologist, lecturer at the MNHN.
Episodes of "Green Sahara" favorable to exchanges and rapprochements
If South Africa and the African rift, in the east of the continent, have long competed as the cradle of humanity, it is because the two regions are excellent "fossil traps", and have been the most searched. To the east, the movement of the tectonic plates made it possible to imprison the bones under layers of sediments and volcanic ash which are very easy to date. It is also in Ethiopia that it was long believed to hold, with Omo Kibish, the oldest fossils of Sapiens, 195,000 years old. As for southern Africa, the skeletons are locked up there in caves, either because the individuals fell there or because they were brought there post mortem by predators.
But the excavations at Djebel Irhoud have changed the situation. And a year later, the journal Science reported that at the Olorgesailie site in Kenya, an international team had unearthed tools that are incredibly "modern" for their age of 320,000 years. The techniques by which they were fashioned had until then only been mentioned in the literature for later artefacts of 100,000 years, notably at the site of Omo Kibish. The authors suggest that groups close enough to Homo sapiens were to populate East Africa while the man of Djebel Irhoud evolved in Morocco. " Homo sapiens did not appear all at once in a specific place , analyzes Jean Jacques Hublin. We are rather witnessing a gradual evolution, with African populations sometimes separated, sometimes close together, over the course of climatic changes, such as the episodes of Green Sahara." Laps of time during which the natural desert barrier was erased in favor of a much more welcoming savannah vegetation. The last such episode ended almost 8,000 years ago.
And the genetics confirm what paleoclimatic studies indicate:this zone may have been favorable to exchanges between northern Africa and the rest of the continent. Analyzes even suggest the existence of human species that are not documented by any fossil. "In the absence of genetic data for these ghost species, it is difficult to determine whether a small group from one point has replaced all other populations on the continent , commented Étienne Patin. Or if the current African populations are the product of ancient interbreeding..."
What we do know is that these exchanges eventually resulted in a fairly homogeneous group, which supplanted all the others. "The transition of the groups that populated Africa more than 300,000 years ago to a 'Modern' Homo sapiens is, in fact, slower and more complex than one might think, concludes Jean-Jacques Hublin. Several pots of milk were bubbling on the same stove:one of them ended up overflowing and extinguished the fire under the others. At some point, Homo sapiens gained a number of adaptive advantages over other groups that were moving in more or less the same direction. The cradle of Sapiens is indeed in Africa... but it is probably all of Africa ."
By Vincent Bordenave