How did humans come to be? | DW Documentary

How did humans come to be? | DW Documentary

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South Africa. These hills are known as the “Cradle of Humankind”. They tell the story of evolution.

Nowhere else have so many of our ancestors’ fossils been discovered. But one mystery remains: When exactly did the first humans appear and what were their lives like? That’s what paleoanthropologist José Braga wants to find out at the Kromdraai archaeological site in South Africa. He aims to give a voice to the bones of our ancestors. Paleoanthropologist José Braga is a world expert in his field; whether with state of the art laboratory equipment or in the dusty savanna, he is searching for the origin of humankind.

And the missing piece of the puzzle in homo sapiens’ family tree. There’s general consensus that all humans living on the planet today have their origin in Africa around one hundred thousand years ago But if you go further back, around 2 Mmillion years, it’s a different story. We still don’t know exactly when the homo genus emerged whether it was 2 or more like 3 million years ago. Here in Kromdraai, close to Johannesburg, Braga aims to solve this mystery. The site is part of the “Cradle of Humankind” and the many fossils in this landscape have revealed the story of evolution.

It has been listed as UNESCO World Heritage Site since 1999. Humanity’s family tree branched off from the great apes seven Mmillion years ago. We and our ancestors are descended from that new genus, the Hominini. One of those ancestors is Australopithecus, of whom several skeletons have been found, some of them over 3 million years old. But about 2 Mmillion years ago, this species died out.

The transition from Australopithecus to human still counts as a blind spot in evolutionary history. No fossil has yet been found from the period between 3 and 2 million years ago that would give us any clues. Braga became site manager of the Kromdraai archaeological site in South Africa in 2002 to try to solve this mystery. At the time the region was mainly living on its reputation. The last relevant discovery came from the 1930s.

And at first, Braga, too, finds nothing new. But he doesn’t give up. He trusts his instincts — and modern technology. What will be important is to record specific geological details on top of your photogrammetry.

Braga thinks Kromdraai is much bigger than originally assumed. To find new excavation sites he uses aerial photogrammetry to carry out 3D surveying. By combining this and chemical soil analysis, he plans to track down undiscovered fossils. And in the end the new survey shows that this soil layer really does stretch far into the north. Kromdraai is five times as large as originally thought. The search for fossil treasure in the unexplored region begins.

The team gathers a large number of samples. Nobody has any idea yet how significant the new finds will be. It’s a piece of eye tooth, from a primate! I’m already in the jaw here! Even before it’s taken out of the ground it’s clear that this is an entire jawbone. Is that from a hominini? It’s extraordinary! Later, after careful cleaning, it becomes clear that this is an almost perfectly preserved lower jaw of a child. It’s a small sensation. But does it belong to a human child or an Australopithecus? Might it even have originated in the mysterious transition period between the two genera? Benjamin Moreno specializes in medical imaging.

He makes a computerized model of the jaw to find some answers. We’re using your data to create a model of the jaw of the “child of Kromdraai” with its tooth buds. That’s extraordinary.

I’ve never seen anything like this in an Australopithecus. They never have these long central or lateral incisors. This backs up my initial impression.

Let’s add some more criteria to make sure this is really a human mandible. The teeth inside the lower jaw have remained unchanged since the death of the child. Their shape and position suggest the genus is homo. But from which precise stage of evolution? What’s special about the child of Kromdraai is that it combines modern and primitive characteristics in a way we’ve never seen before with such old fossils. You can see very primitive Australopithecus characteristics in this eye tooth. But then we also have very clear human characteristics.

If the child had been at a more mature stage of development, we would not have been able to see this. Right, and the fact that it’s a small child gives us some key information. We don’t yet know what constituted a human from a couple of million years ago. I think it was the way they grew up.

But to be able to say that with certainty, we have to find more human infants from this period. Like this one. What makes this find so valuable is its early stage of development. Braga is certain that an immature lower jaw will provide indications of the species.

This would not be the case in a fully developed jaw. Everything points to the fact that the jaw originated in the transition period between Australopithecus and humans. And this is where the problems start with our Kromdraai child. We enjoy some of them, others not so much. I love this one — but it will still be complicated.

We have to date the fossil. Especially whether it’s older or younger than two million years. I’m certain it’s older, but that’s not enough. We need proof. Everything depends on the fossil’s age. But neither the DNA analysis nor the radio-carbon method is able to date such an old fossil.

There’s only one thing left to try. Determine the age of the soil in which the fossil was found. To do this, Braga put together a team of geologists to look for indications of which era the soil and thus the child’s jaw came from.

First, the team has to learn about the composition of the soil in the newly dug area. The almost square site is bordered by limestone. Do you think the blocks are weathered? Yes, totally. Ben, you said it all got completely wet. Yes, definitely water but it’s not circulating. The “standing” water is a bit of a mystery.

And there’s an entire story behind it. A story from the time this child lived in Kromdraai. The secret lies in Sterkfontein caves close to Kromdraai. They found Little Foot in these limestone caves the most complete skeleton of an Australopithecus ever discovered.

It took several years to estimate its age it was 3.7 million years old. Laurent Bruxelles headed up the team at the time. He knew this cave labyrinth and its history inside out. Here we have small passages that map the creation of the cave.

You can see the process. We’re below ground water level. So everything is under water.

The water drips slowly and gradually dissolves bits of carbonate and magnesium. Sand and anything that dissolves easily is washed out. This is how labyrinthine grottos form — dozens of kilometers long.

These discoveries from the Sterkfontein cave forced the team in Kromdraai to think again. The geologists found the same disintegration process in the rocks of both caves. So the two locations seem to be connected underground.

The opening to the earth’s surface has to be a remnant of collapsed corridors. That means that the site in Kromdraai was once an underground cave. For Braga and his team, this is an important realization.

They want to understand when and how the cave filled up. Is this the key to dating the child of Kromdraai? To an indication of the origin of humankind? We’re in one of Sterkfontein’s larger halls. It’s about thirty meters long and 20 meters wide and about 30 meters high. That’s exactly the same size as Kromdraai.

This is interesting because here we have an unfilled cave. We still have a vault separating us from the surface. A good 10 meters of rock. But we have to imagine that geological changes are making the roof thinner and at some stage it will open.

Stones will fall in, soil and also animals that we are finding now as fossils. Gradually a pile of rubble will form, called talus. Like in an hourglass. The opening is a trap that over thousands of years catches what used to be on the surface. It’s a time capsule of what was happening outside at the time. The talus rises until the opening is clogged again, perhaps due to a collapse.

Once the hole closes everything below it becomes fossilized. At the same time, stalagmites grow slowly in the cave. As soon as the hole reopens, a second pile of scree forms on top of the first. In Kromdraai, the former cave roof was completely eroded.

So the scree that the fossils were embedded in was exposed. Here we have a snapshot of what Kromdraai must have looked like 4, 5 or 6 Mmillion years ago, before the cave opened to the surface. At first sight, everything seems to come from one source. But electromagnetic measurements show that there are actually different layers, each from a different epoch. The geologists try to date the layer in which the human jaw was found. Braga hopes to then be able to estimate the age of the Kromdraai child.

The incisor of a bovid. Jean-Baptiste Fourvel specializes in animal fossils. He identifies the type and evolutionary stage of the fragments.

The bone fragments help date the animal species. This is a femur. From what? A bovid? Yes. Fourvel thinks this was a small antelope.

From the same period as the child of Kromdraai. But what does that tell us? I’m trying to put the puzzle together, piece by piece. From the death of this animal to today. These finds help us understand the ecosystem the hominini developed within.

The bovid fossils suggest open or wooded savannah. But that says little about the age of the layer since today’s antelopes are too similar to their ancestors 2 million years ago. To determine the age, the teams need to find animals whose anatomy has changed more. After a few hours, they find a solid block containing fossilized bones of an unknown animal. Fourvel carefully exposes the sample with a dentist’s cutter.

He has to be very careful not to damage the fossil. I thought it might be a feline predator. After cleaning it, I have the complete gums and saber teeth of a 2 million-year-old feline predator, a Megantereon. It’s the breakthrough they were hoping for. This saber-toothed tiger appeared about 3 million years ago in Africa and died out about 2 Mmillion years ago. The layer the animal gums and the child’s jaw were found in, is, in fact, from the transition period between Australopithecus and human.

But the team has to date it even more precisely. The geologists get to work again. They use a stalagmite from the former cave to measure the time. This is THE stalagmite from Kromdraai, the “Cradle of Humankind”. It’s the only one we know is still in place, and it can be backdated.

Stalagmites are formed from drops containing tiny amounts of uranium. Over time the uranium turns to lead. The ratio of the two elements reveals the age of the stone. This stalagmite must be between 2 and 2.3 million years old.

The talus under the stalagmite must be older. This proves that the fossils from the talus below the stalagmite are also more than 2 million years old. Further indications that the child’s jaw comes from the transition period from Australopithecus to human. Kromdraai gives us exactly what we were missing in Sterkfontein the connecting piece between Australopithecus and hominini.

In Sterkfontein these layers have been lost due to erosion. In Kromdraai they are still there. Here we can bring together the links between all of the stories from the Cradle of Humankind. It’s a spectacular discovery. The child of Kromdraai is the oldest human child ever excavated. An examination of the lower jaw discloses the age of the first humans.

It also shows us what differentiated them from Australopithecus. We can count on the fingers of one hand the number of finds we have from the period before 2-to-3 million years ago. And never a child. But in Kromdraai we have this infant who is showing us what humans were like 2 million years ago. We made a 3D image from the data to compare the lower jaw of a 2-year old today with the Kromdraai child and the Taung child. The iconic Australopithecus child.

The Taung child was discovered in 1924 in South Africa. At the time it was the first and only Australopithecus. At the time, it didn’t generate much interest since it was thought that fossils of children did not provide much information. It’s hugely important for Braga however, as it helps to differentiate modern-day humans from earlier genera.

The Australopithecus child in red, Kromdraai in blue that’s what it looks like today. We can get into about half of the jaw here. Great. The Taung child really has no chin. It’s slanted.

A receding chin. The Kromdraai child has quite a vertical profile, very different to this here. The chin does not recede as strongly as the Taung one. This symphysis area is also less broad.

And there’s the morphology of the tooth, which differs a lot from the Australopithecus. We have a series of characteristics here that suggest it is closer to a modern-day child than to an Australopithecus. It changes everything. It’s much more modern than we thought.

So the criteria that defined what humans are - are now outdated. Walking upright, using tools, the large brain. Now we know that Australopithecus also used tools and walked upright. The large brain didn’t develop until after the first humans appeared. Today the belief is more that the criteria for becoming human have to do with development. And with the fossil of this infant we are able to answer that for the first time.

The paleoanthropologists realize that this find will revolutionize their research. At Kromdraai, they hope to find out what originally made humans human. While the 3D images are being analyzed, the search for more information continues at the Kromdraai site. Geology provides the researchers with new details. The cave filled up until the talus reached the ceiling.

It’s possible that predators then moved in. The fossils from the talus were probably their prey, and they tell us about the lives of the first humans. 2 Mmillion years ago, we were primarily scavengers, benefiting from others’ leftovers. At the same time we were prey.

It was easy to eat us. So it’s exciting to find the remains of our ancestors who were prey. It brings up new questions around how we continued to develop and change. To find out more about the first humans, the researchers look for new fossils. A comparison of the three jaws, of the Australopithecus, the Kromdraai child and modern-day humans alone is not enough.

To rewrite human history, a comparison is also needed with Paranthropus another hominin genus. “Paranthropus” means “alongside humans” and is considered our close relative. It appears around the same time as the homo genus. There is disagreement about whether it is an Australopithecus or descends from one.

The first Paranthropus was discovered in 1938 close to Kromdraai. The first humans and first representatives of the genus are very different from one another. The Paranthropus has spectacular facial features with an overdeveloped masticatory apparatus. It was vegetarian and specialized in consuming hard plants, contrary to the first humans. Studies suggest that they ate both plants and meat.

So much meat, in fact, that traces of it can be found as a geochemical signature inside their teeth. Braga wants to unravel the origins of humankind. To do this, he would have to compare how human children and Paranthropus children developed over 2 million years ago. The problem is that no Paranthropus child has yet been discovered. Braga hopes to find one in Kromdraai. He brings a specialist on board to find out where to dig.

Mantombi N'goloï will use the latest technology to lead him to the right place. She can predict where the largest number of fossils are to be found. My specific area of studies is on the 3D reconstruction of the site, and understanding special patterning using 3D digitization methods. These are actually the fossils whose coordinates we have collected using the total station. And in red we have the bovids, and in green we have the hominins and in yellow we have carnivores. So what we see from our 3D analysis is that we actually have four main clusters.

Cluster one and two contain the most fossils so this is the most dense region of the site. Archaeology is a very destructive process. And part of the discovery is destruction, but my function within my PhD is to ensure that we can actually preserve data in such a way that future generations can have an image of what it looked like before it was removed.

Compared to the apartheid times, I think now there is more knowledge and awareness of this and a lot more representation as well, so me, for example, being a black woman studying this, it’s very rare but we are pioneering and opening spaces for us to know our history and disseminate it as well. Braga digs where Ngoloyi locates the highest probability of finding hominin fossils. This looks like part of a tusk, completely disintegrated. The ivory goes in all directions, a typical find that tells us absolutely nothing. It only shows us the inclination angle of the layer.

Benji! Come over here! I think we have an incisor here that’s in the opposite direction to the layer with the Paranthropus. Yes, that’s clearly north to south. It fits the hypothesis that we have another entrance, and another source of material. Even older? Yes, older. That indicates a much longer, more complex history. The elephant tusk is important after all.

Its position at right angles to the other finds reveals that it belongs to a different talus. Presumably from another opening in the cave roof. This talus is partially covered by the one that contains the first humans and Paranthropuses.

So it’s older. But how old exactly? The excitement grows. This layer is very rich.

The yellow parts are bones. To know what they are, you have to take them out. But it’s too hard for the tool. We’ll need other tools for that. Recovering the fossil from the solid ground takes time.

But too much air-exposure can damage the bones. To avoid this, large blocks are cut up and taken to the Sterkfontein laboratory. There, the fossils are extracted. The Sterkfontein lab belongs to Ron Clarke, the discoverer of Little Foot. He rarely opens his lab — but Braga’s find awakens his curiosity.

This piece corresponds to the right maxilla of that specimen. So it still needs preparation. Yes, but, wow! It’s all yours. This is already piquing my interest. This doesn’t look like a Paranthropus, between you and me. At the moment in the matrix, it’s not that easy to tell.

What about the premaxilla? But if you look at the premaxilla, it doesn’t look like it’s from a homo. I’ll get something for a comparison. Yes... and also two fifty two. The more I look at this the more I feel like it’s one of these. For the first time now in Kromdraai, you have an Australopithecus. I’m sure of it.

I'm so pleased for you. And pleased for the science, because this way we learn more about the way these hominids evolved and the different species that existed at any one time. Well done! The last fossil brings the real sensation. Kromdraai is the only site in the world that preserves the transition from Australopithecus towards Paranthropus and man. These are the three crucial pieces of the puzzle to unravel the origin of humankind.

This Australopithecus specimen is very close to the fork in the family tree. It may be one of the last before Paranthropus separated from humans. And what’s so interesting in Kromdraai is that in the layer with the skull, we found both the oldest Paranthropuses and the oldest humans. So it really records the moment when the transition happened.

To find an Australopithecus that lived well before the split or a Paranthropus longer after that... is quite interesting. The more skulls you have, the better. But I'm more interested in the blank page in the history book the moment when the species separated. Braga knows he’s witnessing a historical moment, one that many of his colleagues will envy him for. We are touching our ancestors here, and their descendants. Kromdraai is a time machine.

But Braga is missing one essential element. What exactly was the difference between human and Paranthropus children 2 million years ago? He’s convinced that this is the key to understanding how humans came to be. Finding another Paranthropus baby towards the end of the dig seems unlikely. Will Kromdraai reveal its last secret after all? Look. I have the bottom teeth, another row of teeth.

Progress! Yes, I have the incisors. For the first time we are coming face to face with a Paranthropus baby. Every time I’m here, I hope to find either a human baby or a Paranthropus baby. Welcome little Paranthropus We’ll learn a lot from this child when we compare it to a human baby whose jaw we also found. The piece of jaw is the pinnacle of Braga’s work. At last he can compare a Paranthropus baby with the human baby, that he found at the beginning.

What can the Paranthropus baby tell us about becoming human? This child is the new star of South African paleoanthropology. It’s the first Paranthropus child skull ever discovered, worldwide. Using a particle accelerator called a synchrotron, we are creating a three-dimensional X-ray image of the inside of the tooth.

These 5-micrometer-thick structures correspond to the enamel that is deposited in a baby in 24 hours. Similar to the annual rings of trees, the thicker the deposit, the faster the tooth has grown. We found that the teeth of small Paranthropuses grew significantly faster than the teeth of small humans. We also saw differences in geochemistry. The ratio of calcium isotopes in the human and Paranthropus teeth gave us information about nutrition as the tooth formed. This is important because the isotope ratio changes during the transition from lactation to solid food intake.

Tooth analysis showed that Paranthropuses were weaned very early. Probably shortly or a few months after birth. Humans, on the other hand, were weaned much later, not until about age three. This had implications for social life, since raising a child that was weaned much later required much more effort from the parents and the group than a child weaned earlier. A correlation between the duration of childhood and social structure can already be observed in great apes a connection that may be transferable to the first humans.

Sabrina Krief studied the behaviour of different primates in the jungle and supports Braga in his analysis. Gorillas are weaned much earlier than chimpanzees. Before weaning, metabolism focuses on brain development and cognitive skills. They learn to walk and climb later. The young chimpanzee clings to its mother’s belly and is completely dependent on her. The community helps to defend the youngest.

Young gorillas, on the other hand, become independent much earlier than chimpanzees. Contrary to what you might think, this shortens their learning period. You see chimpanzees starting to use tools during a longer learning phase. This takes time and the support of the big ones. When I watch chimpanzees, I feel very close to them. They’re like part of my family.

And if you imagine the first humans, how they lived together, it was like this. The big difference with humans is that the chimpanzees’ tools remain the same to this day. They pass on the knowledge to the next generation.

But there was no progress, no further development of the tool. And that's probably the difference with humans. Our culture grew steadily. We perfected our tools bit by bit. So primitive humans’ childhood was much longer than that of the Paranthropus.

The analogy to today’s great apes allows conclusions to be drawn about how hominini organized their societies 2 million years ago. The first groups of people seem to be united by one main goal to protect their offspring. This makes the group vulnerable, but apparently favours the passing on of knowledge.

For Braga and his colleagues, this is the long sought-after key to being human. Kromdraai is the proof that humans’ strategy was the better one, since the Paranthropus disappeared one million years ago. Humans, on the other hand, have evolved in an original way compared to Australopithecus and Paranthropus. The human reproductive strategy means giving birth to offspring that need a lot of energy and attention to develop their brains. This strategy prevailed.

It allowed our species to populate the entire planet. As descendants of a species that, I am convinced, already lived as we do. At least as far as the relationship with their children was concerned. Braga’s spectacular finds bring us closer to our ancestors. The fossil molars show that the secret of our species is the long lactation period. This evolutionary step is what made the unique development of humans possible.

2023-01-20 13:58

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