Until recently, the official theory was that Homo sapiens, our species, evolved in East Africa around 200,000 years ago, and then spread to the rest of the world. A simple, linear and somewhat comforting idea. … But in recent years, new discoveries in places as far from Ethiopia as Morocco or South Africa show that everything was not so simple. And that the first Homo sapiens already existed, in different regions of the African continent, more than 300,000 years ago.
However, a new study recently published in ‘Nature’ by researchers from the Swedish University of Uppsala and based on the analysis of the genomes of 28 people who lived between 10,200 and 150 years ago in southern Africa has just confirmed that this region has indeed played a major role in the evolution of our species. There, a group of humans like us lived in near-total isolation for hundreds of thousands of years, perfecting the genetic tools that made us who we are today. It is the largest study of ancient African DNA to date, and its results rewrite the history of our species.
The end of the “East African theory”
The so-called “East Africa theory” began to falter almost a decade ago, in 2017, when a team of paleontologists from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, discovered the fossil remains of five anatomically modern humans, but aged between 300,000 and 350,000 years old, at the Jebel Irhoud site in Morocco. It was an earthquake. Suddenly, our species was almost twice as old as we thought, and its origin could no longer be limited to a single point on the African map. Furthermore, if there were already modern humans in North Africa 300,000 years ago, what was happening in the rest of the continent?
New study reinforces idea that origin of Homo sapiens is not a specific event in Ethiopia
Part of the answer came just two years later, in 2019, when a new study “pulled the genetic thread” and located the first lineage of our species, through the maternal line, in southern Africa, more precisely in the Zambezi River basin. All this led researchers to think that, long before Homo sapiens left Africa to conquer the world, it had already spread widely across the black continent.
Led by Mattias Jakobsson, the new study confirmed this point. An investigation that is extremely difficult to carry out, a veritable logistical and chemical nightmare. And extracting ancient DNA in a part of the world where heat and humidity degrade genetic material at a rate unseen in the colder climates of Europe or Siberia is a true technical feat. The complete genetic sequences of 28 individuals therefore constitute, in scientific terms, a treasure of incalculable value. This is the largest study of ancient African DNA carried out to date.
First surprise, they were isolated
Comparing these ancient genomes with those of modern humans and other Stone Age remains from around the world, researchers stumbled upon something unexpected. These southern humans were not just another branch of our evolutionary tree, but the survivors of a population that had remained genetically separated from the rest of humanity for at least 200,000 years. In other words, while in other parts of the world populations mixed, migrated and changed, in southern Africa there was a stable group, a sort of human “gene pool”.
“We knew that southern Africa had been inhabited for a long time,” says Jakobsson, “but we didn’t know if they were our ancestors, true Homo sapiens. “Now we can prove that they were, that our species has existed and evolved there for a long time.”
The stability of this group seems almost miraculous. The remains of the 28 individuals found, most of which come from the Matjes River rock shelter and whose ages range from 10,200 to 150 years, show that over these ten millennia the tools they used changed. There were fashions, there were technological innovations, stone cutting techniques evolved. In Europe, when we witness such a change of tools, we tend to assume that a new people has arrived to replace, or at least complement, the previous one. But not here.
There were “evolutionary laboratories” in the north (Morocco), in the east (Ethiopia) and now, we know, without a doubt, also in the south.
Here the DNA tells us that, millennium after millennium, they were genetically the same. “There is no evidence of immigration or population exchange,” the study notes. Which suggests that the cultural and technological innovation we see in the archaeological record of southern Africa was not imported, but local. In other words, the complexity of modern human behavior, abstract thought, and advanced technology emerged among us.
Brain…and kidneys
By studying these genes, researchers have discovered up to 79 DNA variants unique to Homo sapiens. That is to say genetic instructions that Neanderthals, Denisovans and of course chimpanzees do not possess. They constitute, in essence, the unique “code” of our humanity.
And what functions did these exclusive genes perform? Scientists expected to discover, as usual, changes related to the brain or the immune system. And they found them, of course. They discovered genes linked to neuron growth and complex cognitive functions.
But the biggest surprise came from another part of the body: the kidneys. And seven of these variants exclusive to our species affect kidney function. Why would evolution bother tinkering with the kidneys to create modern humans? The answer, according to Jakobsson, might lie in one of our most underrated skills: sweating. “One hypothesis,” says the scientist, “is that these variants are linked to humans’ unique ability to cool the body through sweating.”
While in other parts of the world populations mix, migrate and change, in southern Africa there is a stable group, a sort of human “gene pool”.
Something that, if you think about it, makes perfect sense. Unlike other primates, or our Neanderthal cousins (who were adapted to the cold), Homo sapiens is “designed” to withstand hot climates. We can run marathons in the sun because our cooling system is exquisite. But sweating requires extremely precise control of water and mineral salts. And that’s the job of the kidneys.
Therefore, it is very likely that these “kidney adaptations” allowed our southern African ancestors to hunt during the hottest hours, when predators were asleep and prey were exhausted, a powerful evolutionary advantage over other hominid species.
The end of isolation
The isolation of this southern group ended relatively recently, just 1,400 years ago, when they began to mix with other groups arriving from East and West Africa. Despite this, his legacy has not disappeared. Today, the San (formerly Bushmen), like the Ju/’hoansi in Namibia or the Karretjie in South Africa, retain an immense part of this heritage in their DNA. In fact, about 80% of their genetic material comes directly from these ancient hunter-gatherers.
Something which also refutes another classic theory according to which the current Khoe-San people descend from a mixed population from all over Africa. The truth is very different: they are the direct descendants of those who remained in the south, the guardians of a “genetic library” which contains, according to the study, “half of all human genetic variation”. The rest of humanity (you, me, the inhabitants of Asia, Europe and the rest of Africa) shares the other half.
A new human map
With the findings from Morocco, the new study reinforces the idea that the origin of Homo sapiens was not a one-off event that occurred in Ethiopia. This was a “pan-African” process. In other words, our species evolved from a network of interconnected, but sometimes isolated, populations over several millennia.
There were “evolutionary laboratories” in the north (Morocco), in the east (Ethiopia) and now, we know, without a doubt, also in the south. Marlize Lombard, co-author of the study, sums it up perfectly: The complex behaviors and modern thinking we see in the archaeological record from 100,000 years ago “originated locally” and from the south they were able to filter north, traveling with the genes and technologies of these hunter-gatherers.
In short, we are rewriting the first chapter of the biography of our species. And it turns out that, to understand how we conquered the world, we must first understand how, over hundreds of thousands of years, we learned to survive, think and sweat under the hot southern African sun.