Uunder our skins, we are all African. This is the recent and simple conclusion of scientists studying the origins of our species. Genes, ancient tools of stone and fossil bones – analyzed in recent decades – make it clear that today men and women are the direct descendants of hunter-gatherers who evolved somewhere in Africa and took control of the continent before a group left to conquer the rest of the world tens of thousands of years ago.
However, where exactly in Africa we first appeared has never been established. Some researchers claimed that the cradle of humanity was located in the east, Ethiopia or Kenya. Others put their money into South Africa. But most were sure that it would be only a matter of time before the birthplace of our species was identified: perhaps on earth that covered a large estuary that once groaned with fish or near a large slice of savannah rich in game. It was here, in a stone age paradise, that our most primitive predecessors honed their intellectual and cultural skills and were transformed into Homo sapiens, a species of primate known for its rounded skull, its small face, its prominent chin, advanced tools, high intelligence and sophisticated culture.
It is an orderly image. However, cracks in this simple image of our distant past have begun to appear in recent years, mainly because plausible candidates for our hometown have proved difficult to find. As a result, an increasing number of researchers are moving away from the idea that such an Arcadia existed. As Harvard geneticist David Reich said: “When it comes to human origins, there was no Garden of Eden.”
Instead, archaeologists, fossil experts and geneticists advocate a dramatic new idea to explain the evolution of Homo sapiens. They say that a multitude of different places in Africa has been the cradle of modern humanity. We did not appear in one place and then spread. Instead we have been constantly evolving for nearly half a million years across the sprawling vastness of the continent.
Chris Stringer, of the London Natural History Museum, explains. “The immediate predecessors of modern humans probably arose in Africa some 500,000 years ago and evolved into separate populations,” he says.
“When times were bad – for example, when the Sahara was arid, as it is now – small isolated pockets of humans would cling to existence. Some of these people would have died out. Others managed to resist. “
Later, when conditions improved – for example, when the Sahara turned green again and lakes and rivers formed – the surviving populations expanded and came into contact with each other. When they did, they would exchange ideas – and genes. So the climate would be dark again and they would separate.
“This has happened several times in different places for different reasons for the next 400,000 years,” adds Stringer. “The end product was Homo sapiens, the species that is more or less the version of modern humanity that now inhabits all continents on Earth. “
This point is supported by Eleanor Scerri, of the University of Oxford. “Homo sapiens probably descended from a group of interconnected groups of people, who were separated and connected at different times. Each had different combinations of physical characteristics, with their own mix of ancestral and modern traits. “
Normally, animals that spread across a continent tend to divide into several subspecies and eventually evolve into completely new species. In case of Homo sapienshowever something very different happened. We have maintained connections, probably due to our species’ propensity to long-range social networks, and instead it has evolved slowly but en masse throughout Africa.
In other words, our socialization has strongly influenced the course of our evolution, a point underlined by geneticist Mark Thomas of University College London. He argues that culture – the accumulation of knowledge, beliefs and values in a society or tribe – has been vital for our survival. “Without culture we would be dead,” he says. “Today we know things that were developed by ancestors tens of thousands of years ago and that have been passed down through the generations. Culture is our life support system. ”
One reason for the earlier belief that humanity had a single place of origin can be traced back to the work of early molecular biologists, such as Allan Wilson of the University of Berkeley, California. In 1987, his team used genetic analysis to study mitochondrial DNA, a form of genetic material inherited exclusively from mothers.
By comparing the variations in the mitochondrial DNA of selected individuals from all over the world, Wilson was able to create a giant family tree for humanity, which has firmly rooted in Africa. However, Wilson went further. He claimed that this genetic tree could be traced back, not just to a group of Homo sapiens but for a single mother, a mitochondrial matriarch who gave rise to all our species.
The idea that an African eve existed was very influential. If there was a single mother for humanity, then she must have lived somewhere and thus the idea was born that there was a specific place that was our homeland. Over the decades, many contenders have been proposed as sites that may have been the cradle of humanity, including a recent suggestion by scientists who claimed that mitochondrial DNA indicated that humanity’s roots could be traced back to Botswana.
Many researchers no longer believe these simple explanations, however, and point to other studies that seem to confuse them. For example, analyzes of the Y chromosome, which determines virility in humans and is therefore inherited exclusively through the male line, suggest that modern humanity probably originated in West Africa – because the largest variation in DNA is found of the human Y chromosome there, and DNA variations tend to increase over time.
In this way, the rather strange situation is presented in which our African Eve inhabited a part of the continent while her Adam appeared in a different and distant part of the continent. It’s not a good way to start a dynasty, one would have thought.
And then there is the human skull. The oldest rounded, modern and humanoid skull was found in Ethiopia. At the same time, the oldest symbolic expression in terms of engraving and art is found in the Blombas cave in South Africa, while the oldest symbolic burials are located on the other end of the continent, just outside Africa in Israel, where in a chance, a 100,000-year-old tomb was found to contain a body adorned with deer antlers.
“There is no evidence that a single part of Africa has produced all this modern behavior,” says Stringer.
Instead, it is claimed that for much of our existence, different groups of humans showed some but not all of these constellations of characteristics before they were slowly shared as our social networks expanded. As people mixed, they collected biological and behavioral solutions that had already been tested by other populations.
Slowly, success built on success and modern humanity have emerged in all its glory and sophistication. There has not been a sudden turnaround between a group of people who have acquired symbolic thinking, laziness and art in a single evolutionary event. It was more a question of mutual exchange of intellectual and genetic attributes over large distances and long periods of time.
A big problem in understanding this notion stems from the fact that ancestors are so often explained in terms of trees, whether as a family tree or an evolutionary tree that traces how species derive from others. They have single trunks that divide into branches and focus thoughts towards individual origins.
“It’s a powerful metaphor but it also turns out to be deeply flawed,” says anthropologist John Hawks of the University of Wisconsin-Madison in a scientific newsletter article Aeon. Instead he claims that our evolutionary history is more like a braided river, a band of streams that intertwine in and out of each other before merging for hundreds of thousands of years in the same huge canal.
However, a cautionary note is issued by the geneticist Pontus Skoglund at the Francis Crick Institute in London. “We have to be careful, because we are talking about events that happened hundreds of thousands of years ago. The problem is that we only have ancient fossil DNA that is a few thousand years old. This makes it difficult to be completely certain about how populations interacted in those distant days. We need more evidence. “
This point is recognized by Stringer. “The problem with DNA is that it starts to fail after death, and that the warmer the conditions, the faster that process occurs,” he says. For parts of the world where it is relatively cool, for example in Europe or in deep caves, this is not a problem. DNA that is hundreds of thousands of years old was found in these places, extracted and studied. But in Africa the heat is a real problem.
“Limit the type of evidence we can gather,” adds Stringer. “We are like the proverbial drunk who dropped the keys on the street but can only look where the lamppost shines – because it is the only place where he can see – even if his keys are in the dark. We are limited to where we can look. We have to keep this in mind. “
However Stringer and other advocates of the Pan-African theory of human evolution are confident that this completely new way of seeing the appearance of our species in Africa will bring new insights into the development of human societies, not only in the past 500,000 years but also point seven million years ago, when the lineage that led to Homo sapiens separated from other primate lineages in Africa.
“What inspires most of the intertwined flow of our origins is what it implies for future discoveries,” says Hawks. “During the seven million or more years of hominin evolution, there must have been dozens of such enduring populations, sometimes mixing and sharing adaptations with each other. Many others are out there, waiting for anthropologists to bring them to light. “
The birth of art
A few weeks ago, researchers announced that they had made a surprising discovery on the Indonesian island of southern Sulawesi: a mural painting depicting men and animals. Using a technique known as uranium and thorium dating, Australian and Indonesian scientists showed that the work was approximately 44,000 years old, the oldest known rock art created by our species.
The painting consists of six mammals – two Sulawesi warty pigs and four dwarf buffaloes – and several human-like figures, one with a bird’s head, another with a tail. The images suggest that a myth or legend is taking place on the cave wall.
“It has all the key elements of modern human cognition: a narrative scene and human-like figures that don’t really exist in the real world,” says Professor Maxime Aubert, at Griffith University in Australia. “Everything has been there for 44,000 years ago.”
South Sulawesi is located thousands of miles from Europe, home to practically all other paleolithic rock art. And that formidable geographical gap is important. In Europe, the beautifully represented mammoths, lions and rhinos of the Lascaux, Chauvet and Altamira caves show that something special was going on in the heads of their creators. They thought symbolically letting one thing, brushstrokes of paint, replace another: an animal. These artists infused meaning into their lives beyond the basic impulses for survival.
This evident refinement led some scientists to conclude that the early Europeans were, intellectually, more gifted than other early members Homo sapiens. Perhaps a genetic mutation occurred in their brains when they first entered the continent from Africa.
Always controversial, the concept has now been firmly canceled by the dating of the Sulawesi caves. His art is 10,000 years older than Lascaux or Altamira, but is equally sophisticated.
“The idea that cave art began in Europe has clearly proven to be wrong,” says Stringer.
In other words, Homo sapiens reached its capacity for symbolic thinking, narration and abstract thinking long before we arrived in Europe 40,000 years ago. Neurologically we were already fully armed and we were already armed for a long time before we emerged from an African homeland 70,000 years ago to conquer the world. These were the skills that had been honed for hundreds of thousands of years across Africa.