Why did early hominids stop climbing trees

Paleoanthropology In the den of the human

It is early afternoon, around 40 kilometers northwest of Johannesburg in South Africa. The road becomes single lane and turns into a gravel road. Hilly savannah as far as the eye can see. Only a few trees can be seen here, otherwise brown grass grows everywhere, sometimes as high as a man.

In the den of the human. Genealogy in South Africa

From Michael Stang

Arend Mothokgo welcomes the international group of visitors with a big grin. Behind him a café, a small museum and a tiny museum shop. They are part of an underground cave system that extends over 47,000 hectares beneath the South African landscape.

It's windy and raining a little. Arend Mothokgo hands out protective helmets. Everyone covers the path quickly. There is only a few artificial light in the cave. The few flashlights barely illuminate the bare stone walls.

"This cave was discovered in 1896 by Italian miners who were looking for gold. They did not find it, but plenty of lime. There was also a great need for the production of cement, toothpaste, soaps. They blasted the rocks here. The Opening here is not a natural entrance either, everything has been blown up. "

It's getting damp. An underground lake lies peacefully on one side. Mothokgo warns that the water would have killed some careless cave visitors. Today everything is secured with railings. It goes on.

Arend Mothokgo points up. There, 25 meters above him, the rock of the Silberberg Grotto opens up, a little daylight can be seen.

Three million years ago one of our ancestors fell into the cave here and died. Half monkey, half human. In 1995, researchers first discovered four foot bones and named their find "Little Foot". A misleading name, because actually there were not just a few bones, but an entire skeleton, firmly buried in the rock. It was the world's first complete skeleton of an early man. And the beginning of a new era for paleoanthropology.

"Ten years ago we could expect, with a lot of luck, to find perhaps a handful of fossil fragments in a year. That has completely changed."

Lee Berger from the University of Witwatersrand in Johannesburg.

"We not only discover more and more fossils, but they are also spectacular, we find complete skeletons, different individuals of an early human species. That is of course something that our research direction has to fight against."

The story of South Africa begins in 1924, when Francis Thackory, director of the Institute for Human Evolution at the University of Witwatersrand, explains that the country first made a name for itself.

"A skull was discovered here in a place called Taung: 2.5 million years old. Professor Raymond Dart described the find as a new species, which he named Australopithecus africanus."

The name means something like: The monkey from southern Africa. It was the first description of an Australopithecus; that genus from which our genus Homo arose.

"The find was ape, but also very human. This creature had a small brain, but already walked on two legs. Suddenly South Africa played an important role in the incarnation, because now there was proof of Charles Darwin's theory that the cradle mankind in Africa said that mankind developed there. "

Replica of the fossil skull of the "Child of Taung" (picture alliance / dpa)

Only the facial skull, the fossilized brain and the lower jaw remain from the Taung child. But that was enough to reconstruct its end. A bizarre story: an eagle must have grabbed the child by the head and carried it away. The body was torn off, the head finally landed in a crevice and petrified. The claw prints of the bird of prey can be clearly seen in the eye socket.

The all-important question: where does the homo genus come from?

Since then, fossil collectors have repeatedly visited the karst caves in South Africa, but the yield has remained meager. They had better luck in the east of the continent; Generations of scientists discovered fossils from the early days of man, especially in the Ethiopian highlands. But it was just a few bones. Always at great intervals on the timescale of the Incarnation. Piecework that was more difficult than right to work with.

"Paleontology shows us snapshots from the past, but the findings are not always complete. Our challenge is therefore to discover as many fossils in as many caves as possible, to bring them all together and to bring them into context."

The great challenge lies between two and three million years ago. That time when our direct ancestors developed. The all-important question is: where does the homo genus come from? South Africa may be able to answer that question.

When in Sterkfontein, Little Foot, a complete skeleton was recovered for the first time in painstaking detail work, Lee Berger had been teaching at the responsible University of Witwatersrand in Johannesburg for several years. He too dug in the caves near Sterkfontein, especially at a place called Gladysvale. The success was moderate. By 2008.

"At that time I started evaluating satellite images and creating a new map of the area. We discovered that there aren't just 100 caves here, as previously assumed, but around 700. And we discovered fossils in 60 of them."

Lee Berger had identified a potential site that he wanted to take a closer look at. He set off with a colleague and his then nine-year-old son Matthew.

"I said, okay, find fossils then. Matthew ran and a minute and a half later he found a rock, picked it up and said, Dad, I found a fossil."

Matthew had come across a hitherto unknown early man. A major excavation followed, during which Lee Berger's team recovered the two million year old remains of several individuals, including two very well-preserved skeletons, that of an adult woman and that of a boy. The new bones belong to an early human species that was given the scientific name Australopithecus sediba. He was already walking upright, his hands looked like today's people. Other games, on the other hand, still looked very primitive. An ancestor very close to modern humans - whose roots were supposed to be in East Africa.

Connection between prehistoric and early humans: Australopithecus sediba. (Science / University of the Witwatersrand, Lee Berger, Brett Eloff)

"Sediba punched a hole in this idea. Either he was a direct ancestor of our genus Homo, or a dead branch in the human family tree. Its anatomy raises big questions. How and where did our genus Homo come about? And how do we explain what we do are?"

The answer is obvious, says Lee Berger. "We have to look at the fossils from southern Africa. This is the only way we can understand what happened in human evolution."

In Johannesburg, at the University of Witwatersrand, Bernhard Zipfel, South African with German roots and master of the bones, leads into a large room. Here are - openly accessible to all scientists - those early human fossils that made South Africa famous.

"Well, it's hard to believe: just this little compartment here, so that's two rows, that was our whole collection of hominids before, collected over many, many years."

"Here we have an Australopithecus africanus skull, this one is StW504 and 505, these two."

The Taung child lies here too.

"And on this side it starts with the original fossils from Sterkfontein."

And next to it, in the middle of the room under glass, the two Australopithecus Sediba skeletons.

"You can see how quickly it all changed. So few fossils for so many years and then suddenly you have so many overnight."

Bernhard Zipfel points to the ankle of the female skeleton. Then he takes out of a box a replica of three bones that had given the anthropologists a big headache, especially the heel bone. Had it not been discovered in the skeletal system, no one would have associated it with the rest of the body:

"If it had been from one place, I would have said: this is human, from another place, I would have said this is a primitive monkey from the Miocene or something like that, but they are from the same individual."

The ankle is a mixture of old and new anatomical features. While the bones look very primitive in themselves, they are already very modern in their function, as in the case of representatives of Homo. The ratio of arm length, which is very apelish, to the shape of the hand, which appears human, shows the mosaic-like anatomy of this early man. The analysis suggests: The simple concepts of the Incarnation - a quick and smooth transition from primitive to modern - cannot be right.

"That tells us that some parts of a skeleton evolve faster than others and that that might not make complete sense to us. You also have to think that these are primates that could walk upright, much like we do, but they do." could also climb trees and they also have arms and legs that could do that. "

Three to two million years ago no humans lived in South Africa, but there were various types of early humans. What events laid the foundation for our genus Homo to develop from them? To understand that, Job Kibii looked at environmental issues.

"Two million years ago everything looked different here. Where we have the caves of the Cradle of Humankind in Sterkfontain today, there were wooded areas, some of which merged into open grasslands. We have evidence that there were lianas back then. These." There are climbing plants in Africa today only near the equator like the Congo. "

The climate changed noticeably back then. It rained less and less, the forests disappeared and were more and more replaced by an open landscape.

"Once there were these savannah areas, then again tropical forests. So Australopithecus sediba must have been adapted to all these conditions back then, two million years ago."

The ability to warn each other

Australopithecus sediba faced several predators at once; with leopards that live in the woods, but also with hyenas that roam the open savannah. From comparative studies with today's monkey species it is known that under such circumstances the ability to communicate offers a survival advantage.

"Early humans therefore had to be able to communicate well and warn each other, for example 'if you go there you will meet this attacker, if you go into the savannah you will meet that one.' That's what we suspect. "

"Thanks to this ability to communicate, the people there have developed further until we are today as a kind of end of the line."

In Sterkfontein, Arend Mothokgo brings his visitors back into daylight. He leads the way, along a path with wooden planks, to a second, the natural entrance to the cave - a large, jagged hole in the rocky underground. He's pointing down.

It was here in 1947 that researchers discovered the skull of Mrs. Ples, who, according to recent findings, was not a woman, but a man. The site is scaffolded. Three men work on the rain-damp rock with a hammer and chisel. The excavations are still far from over.

In the extensive cave systems in South Africa, countless bones have been discovered in recent years, including those of robust, very primitive species that are out of the question as our ancestors. But above all, many hundreds of early human artifacts. All newly discovered fossils come to Johannesburg, where they are examined, X-rayed, prepared and scientifically assessed. A huge mountain of work. Australopithecus sediba alone took the researchers around Lee Berger to complete for four years.

"Sometimes I think that we paleoanthropologists believe too much our own old stories. We think that fossils from early humans are the rarest objects in the world and if we ever find something it will be like winning the lottery. To stay in the picture: But if you don't buy another lottery ticket afterwards, you will never hit the jackpot a second time. "

In any case, Lee Berger was not satisfied with the one big find.

There is also a canteen in Sterkfontein. Museum employees and tourist guides meet here. And cave explorers like Pedro Boshoff, an imposing man with a bald head and a mustache. As always, the geologist and cave climber wears a boiler suit, and he has laid the red checkered hat and bobble next to him while he talks.

"Lee hired me to systematically search all of the caves in the Rising Star System for new fossil sites."

That was in autumn 2013. Pedro Boshoff began to scour the west side of the Cradle of Humankind, a cave system called the Rising Star. In doing so, he came across a tiny entrance, only 17 centimeters wide. Too narrow for the stocky man. He asked two colleagues if they could try. One of them was the spindly Steve Tucker, who joins them with his coffee.

"I'm just one of those lanky guys who can squeeze through such narrow hallways, but so few centimeters were a challenge for me too."

The area was notorious for many accidents.

"I call it the ogre cave. It's dangerous, if you don't pay attention for a minute, you can get very seriously injured very quickly."

But Steve and his colleague were careful.

"It was exciting to go down through this little entrance. The cave is actually known, but nobody had noticed this corner of the system. We discovered a lot of fossils there, but we had no idea how old they were. how many there were or what kind of people they belonged to. "

The two took a few photos and came back upstairs. After Pedro Boshoff saw the photos, he immediately tried to contact Lee Berger.

"It was getting late and I couldn't reach Lee on the phone, so I drove to his house with Steven Tucker. We rang the doorbell, Lee answered and I said, 'You definitely want to let us in.' We were served coffee. I opened my laptop and showed Lee the photos. His jaw dropped down and then we went from coffee to beer very quickly. "

"More than 1,200 fragments of early human skeletons"

This is how the Rising Star Expedition began. Lee Berger decided on a global tender. He was looking for small, agile and cave-experienced young scientists who could leave everything behind and take part in a unique project three weeks later. 50 qualified applications were received, six women were accepted. The one-week excavation was an incredible success.

"At the end of the week we had unearthed as many fossils as had ever been found in Sterkfontein. In the end, there were more than 1,200 fragments of early human skeletons, which are more pieces than all the finds in southern Africa over the past 90 years combined. "

Speaker: A second excavation took place in January 2014, followed by a workshop in May in which all fossils were scientifically examined. One of the leaders of the Rising Star project is the American paleoanthropologist John Hawks of the University of Wisconsin in Madison.

"We numbered 1751 fossils. We can assign many pieces, so we know whether they come from a thigh bone or a shin. Hundreds of bones are complete, and we have a complete hand and a whole foot. We also have more than 150 teeth . "

It is not yet entirely clear how many individuals this corresponds to. There are at least 15 in each case and that is only a conservative estimate. If there are 15 right collarbones, it is easy to extrapolate. 24 ribs, on the other hand, can all come from one person, but also from 24 different ones. The site has not yet been dated. What is clear, however, is that the bones must be old.

"The bones are not human, so they don't belong to our species, it's more what we call early humans."

Only human bones were found in the cave, no clothing or tools, no animal bones. It could be that the bones were washed into the cave.

"We have everything there is in a population. Adults, adolescents, children and babies. Probably women and men."

The rising star bones, like those of Australopithecus sediba, have mosaic-like features. John Hawks cannot reveal much more yet, because the results have not yet been published.

“I think we have a good hypothesis about what these individuals are. It wasn't easy, after all, we had to analyze data from an entire population.And now let's wait and see what the reviewers say. "

The data are to be published in a high-ranking specialist journal in the spring. But that is far from the end of the Rising Star Expedition. So far, just one square meter has been excavated, so many bones were lying on top of each other. Geologist Pedro Boshoff reveals more.

"We all know that here, and I can assure you: there are loads of hominid fossils down there."

Hundreds of new fossils of early humans suddenly appear. Not just individual bones, but entire skeletons, even entire populations, will be analyzed in the coming years. Especially the findings of Australopithecus sediba and those of the Rising Star Expedition show how much science has to rethink. Something is emerging that many researchers could not imagine until recently, says Director Francis Thackory.

"There is this exciting development in paleoanthropology that the boundaries between the individual early human species are blurring. In the past, you could easily assign every new fossil to a new species."

According to the previous doctrine, the genus Homo should have developed from Australopithecus - first Homo habilis, then Homo erectus, and finally Homo sapiens. But the development cannot have been that straightforward. More and more finds appeared, and new names were used. But, did they really represent so many different species? There is some evidence that early humans may have crossed the threshold to the genus Homo in South Africa as well. The new finds thus considerably complicate the image of man's early days. The ramifications in the human family tree can hardly be overlooked. Perhaps it would be better to stop talking about a family tree from a family tree.

The 'luxury problem' of the many finds

"Charles Darwin himself had already recognized the problem. In studies of barnacles, he had noticed that with small samples a species classification - this is species A, this is species B, this one here C - was not a problem. However, the more material he had for analysis The more difficult the categorization became, the boundaries blurred. To solve the problem, he brought the concept of variations into play. "

Paleoanthropologists now also have to face this challenge of putting living beings into categories and giving them names, precisely because there are so many finds at once. Actually a luxury problem.

"And today we have exactly the same problem with our early human fossils in Africa. Today we know 20 species of hominids that are said to have lived over the past seven million years."

Perhaps the old classifications are no longer tenable today, Bernhard Zipfel also admits.

"That was an interesting experience for us now, in which we will be a little more careful in the future when we study isolated bones that we may be careful how we interpret them."

The upheaval in paleanthropology is in full swing. Whether or not South Africa displaces the east of the continent as the richest site for early human fossils is irrelevant. It is becoming more and more clear to the researchers working with Lee Berger that one piece of earth alone will not be able to solve the riddle anyway. The history of the Incarnation is far too complicated for that.

In the den of the human. Genealogy in South Africa
A broadcast by Michael Stang

Director: Claudia Kattanek

Editorial staff: Christiane Knoll