Dawn of Humanity

Deep in a South African cave, an astounding discovery reveals clues to what made us human. Aired June 20, 2018 on PBS

• Originally aired 09.16.15

Program Description                                                                                                    NOVA and National Geographic present exclusive access to a unique discovery of ancient remains. Located in an almost inaccessible chamber deep in a South African cave, the site required recruiting a special team of experts slender enough to wriggle down a vertical, pitch-dark, seven-inch-wide passage. Most fossil discoveries of human relatives consist of just a handful of bones. But down in this hidden chamber, the team uncovered an unprecedented trove—so far, over 1,500 bones—with the potential to rewrite the story of our origins. They may help fill in a crucial gap in the fossil record and tell us how Homo, the first member of the human family, emerged from ape-like ancestors like the famous Lucy. But how did hundreds of bones end up in the remote chamber? The experts are considering every mind-boggling possibility. Join NOVA on the treacherous descent into this cave of spectacular and enigmatic finds, and discover their startling implications for the saga of what made us human.

Transcript

PBS Airdate: September 16, 2015

NARRATOR: What makes us human? Where do we come from? Ever since Darwin put forward the idea that we evolved from apes, scientists have wondered about those first creatures that left the ape world and crossed into ours.

In the last 50 years, fossil finds have filled in some of the many blanks in the story of our evolution, but the bones of our ancestors are few and far between, allowing only glimpses of how we slowly changed, over millions of years, from ape to human.

Now, in South Africa, in caves dangerously deep underground, two new species of hominin, our human ancestors, have been found.

LEE BERGER (University of the Witwatersrand): There it was, right there, one of the most spectacular early hominins ever discovered, lying on the surface of a cave.

NARRATOR: And not just a few bone fragments,…

CAVER: It's everywhere.

NARRATOR: …here, there are thousands.

STEVE CHURCHILL (Duke University): It's just absolutely incredible, the amount of bone that's coming up.

LEE BERGER: Beautiful!

MARINA ELLIOTT (Simon Fraser University): The first thing that came through my mind was Howard Carter's anecdote about opening Tutankhamen's tomb. It was Lord Carnarvon in the back saying, you know, “What do you see?” And Carter says, “Things, wonderful things.”

LEE BERGER: We have found a most remarkable creature and a most unexpected one.

RICK POTTS (Smithsonian Institution): So, we need a new kind of language to talk about this.

NARRATOR: These bones could finally bring our past into focus. What story will they tell about how we became human? A new light shines at the Dawn of Humanity, right now, on this NOVA/National Geographic special.

The high plains to the northwest of Johannesburg have been called the Cradle of Humankind. In the 1930s and '40s, fossil finds here gave us the first important glimpses of our earliest ancestors. Then, for decades, the discoveries seemed to dry up. It looked like the Cradle of Humankind had little left to offer.

LEE BERGER: Go get them. Good luck. Happy hunting.

NARRATOR: But now, from deep caves in the Cradle, come two new discoveries that could reshape the understanding of our ancient past.

CAVER #1: What is it?

CAVER #2: It has teeth.

CAVER #1: It's so solid!

LEE BERGER: There aren't just hundreds of bones; there are thousands of bones. I had never seen or dreamed of anything like the richness of this site.

NARRATOR: …bones that may end up illuminating a critical million-year period in our evolution that has long been a mystery.

BRIAN RICHMOND (American Museum of Natural History): There's a big gap in the fossil record, with only a few little fragments.

NARRATOR: The fossil record suggests that in that gap lies the dawn of humanity, the birth of the genus Homo. It's perhaps the least understood and most important episode in our evolution. Before, it was the world of Australopithecus, an ape-like creature with a tiny brain. Lucy is the poster child for the Australopiths. She walked upright, but belonged to the world of the apes.

VIKTOR DEAK (Paleo-Artist): If I were to see an Australopithecus at the end of a football field, I would probably call the zoo and say, “Hey, an ape has escaped.”

ZERESENAY ALEMSEGED (California Academy of Sciences): The upper part of the body in Australopithecus is, in general, very apish. Go down, look at the pelvis, very human-like.

CAROL WARD (University of Missouri): An Australopithecus is, sort of, like a bipedal ape. If you went back in time and saw them walking around the savannah, you would see animals that stood up and walked like we do, but they would've been smaller in body size. Their brains wouldn't have been as big, so their heads would've looked smaller. Their jaws and teeth were very large.

NARRATOR: The fossil record suggests that somewhere between 2- and 3,000,000 years ago, these ape-like Australopiths evolved into the first recognizably human species: Homo erectus.

BRIAN RICHMOND: They have big brains and small faces, adaptations for using tools.

VIKTOR DEAK: If I were to see, say, Homo erectus at the other end of a football field, I would probably call 911 and say, “Oh, there's a wild man over here, and, you know, somebody should put some clothes on him.”

NARRATOR: So what went on in the transition from the ape-like Australopithecus to Homo erectus? For years, the only species that filled that gap was a creature called Homo habilis. But so little of it has ever been found, the origins of the genus Homo have remained an enigma.

DON JOHANSON (Institute of Human Origins): The greatest mystery, facing paleoanthropology today is to try to understand how, when, where the transition from Australopithecus to Homo occurred.

BRIAN RICHMOND: And what we don't know is what happened between Australopithecus and early Homo. That's one of the big mysteries right now we're trying to solve.

NARRATOR: The prize would be to discover fossil remains that could tell us about that mysterious transition. And now they may have found some.

LEE BERGER: There, you can see two foot bones in articulation.

NARRATOR: Emerging from ancient caves in South Africa are fossil finds of astonishing richness, and not just fragments but virtually complete skeletons.

STEVE CHURCHILL: From the very first block that we had, we had a portion of the mandible, the lower jaw, and we had a collarbone and one of the bones of the forearm. So that was really, really exciting.

LEE BERGER: She's in there.

PETER SCHMID (University of the Witwatersrand): We have a skull; we have a mandible; we have a complete scapula; we have a complete clavicle; we have a complete arm; a complete hand; and half of the pelvis, which we can, with reconstruction, make into a whole pelvis.

NARRATOR: Will these skeletons live up to their promise, offering us a new understanding of the dawn of humanity?

In August, 2013, South African Pedro Boshoff was out of work. He had been a soldier, a prospector, an adventurer and even a part-time student of human origins. Now, he wondered if he could earn some money doing what he loves most: fossil hunting.

PEDRO BOSHOFF (Fossil Hunter): Towards the end of August, I approached Professor Lee Berger, asking if there would be the possibility of a position at faculty with him.

LEE BERGER: Pedro Boshoff came into my office and said, “You know, I really need work, and I have the same belief as you that there is more out there.”

NARRATOR: Lee Berger started exploring the area of South Africa known as the Cradle of Humankind in the early 1990s. After 18 years of searching, he had found only a few isolated fossils. That's not unusual in the field of paleoanthropology.

LEE BERGER: These early human fossils are probably the rarest sought-after objects on Earth. We, in paleoanthropology sit in one of the few fields that probably have more scientists studying objects than there are objects to study. In fact, the vast majority of people who do what I do will never find a single piece of one of these early humans. And if they do, it's going to be an isolated tooth. Probably 80 to 90 percent of our record, just little bits of isolated teeth.

NARRATOR: Just to the northwest of Johannesburg, the Cradle of Humankind is riddled with limestone caves. Some have already yielded fragmentary fossils of our remote ancestors. Lee was convinced there were more discoveries to be made.

LEE BERGER: I had known Pedro for 20 years, and I said, you know, “Go out there. Enlist your caving buddies. Get underground, and see if you can find something.” And so I bought Pedro a motorcycle, so he could move around out here.

PEDRO BOSHOFF: Basically, what he wanted me to do is to go through the Cradle area, locating and finding fossils. So, I sat, as I often do, on a rock, and I contemplated, “How am I going to approach this?” And then it dawned on me, I'm part of a caving society, having caved in this area for years. And in there I found Rick and Steven.

I asked them to systematically work their way through caves and holes towards the east of the Cradle, while I was busy working in the west.

LEE BERGER: We often don't look in the places that are most familiar to us, because we think we know them well. I call it “backyard syndrome.” And so I said, you know, “Start right under our noses. Go to the most well-known places.”

NARRATOR: On September the 13th, 2013, Rick and Steve decided to look into a cave system they thought they knew well. It's called Rising Star.

STEVE TUCKER (Fossil Hunter): It's an amazing cave. It's got a bit of everything. There's tight squeezes, some great climbs, beautiful formations.

NARRATOR: Rick and Steve headed deep underground.

STEVE TUCKER: I wanted to show Rick a great climb in the cave called the Dragon's Back. We climbed up there. And in the process of taking some video of the formations at the top of it, Rick wanted to get past me. So, I went down a small little crevice, basically, so that Rick could crawl over me. I was just getting out of his way. And as I went into it, I noticed that there's still a little bit continuing down.

NARRATOR: Once in the crevice, Steve realized there was nothing below his feet. He squeezed himself further down.

STEVE TUCKER: Every time you go down, it just goes a bit further and a bit further and bit further down. You squeeze your body in so that you don't slip and you feel around for a grip.

So, my legs were dangling down this last little bit, and you don't feel anything below you. And the only way to climb down is actually to lower yourself as far as possible, just keep on lowering yourselves, until your arms are almost fully stretched out, and then you start to feel a couple of rocks you can actually put your feet on.

NARRATOR: He emerged into a hidden chamber. He called for Rick to come down and join him. They could see massive rock formations above their heads. But the real discovery was beneath their feet. The floor of the cave was littered with small bones.

STEVE TUCKER: We saw at first one bone lying around. We looked around a bit more and saw another bone,…

RICK HUNTER (Fossil Hunter): We actually spotted teeth in the rocks and realized we actually had found something.

STEVE TUCKER: …followed by a skull, in the ground. And, finally, one of the most interesting ones was a mandible, with four teeth in it.

NARRATOR: Rick and Steve had no idea what type of bones they were looking at, but they seemed intriguing. They took pictures and decided to show them to Pedro.

PEDRO BOSHOFF: And I will never, never forget when he came to me with his photos, put it on the computer, and the first thing I noticed was the jaw with the teeth. And I realized this is definitely a hominin! So, needless to say, I called Professor Berger. He didn't answer his phone, and we decided we're going to drive to his house. Now, we are all excited, bubbling of course. Arriving at his home, I rung the bell, and when he answered, my words to him was, “Lee, you really want to talk to us!”

LEE BERGER: Pedro says, “You're really going to want to let me in.” And, you know, 9:30 at night, and it's dark, but I could hear that emotion in his voice. They flipped open a computer and I saw something I don't think I ever dreamed I would see on a computer screen.

STEVE TUCKER: A lot of swearing at first. Apparently, that's his reaction when he sees fossils. But yeah, he immediately identified it as a hominin.

LEE BERGER: That was a mandible of what was clearly an early hominin, the teeth just perfect. The next picture had a skull in it, of a hominin, I could see it in outline. There were bones everywhere. They take…every one of them I could see in the image were hominin. I was a bit in shock, because it all went like a car crash for me, you know, it really did, black and white, I have only visual not audio.

NARRATOR: Hominins are all creatures in the human evolutionary line, including Australopiths, Homo erectus and us.

When his shock faded, Lee immediately turned his mind to the question of what type of hominin this might be. From what he could see, Lee thought it was a single individual, probably one of the Australopiths that came on the scene some 4,000,000 years ago.

The photos were hard to make out. Lee wanted to know if the bones in the Rising Star cave were similar to fossils he had discovered five years earlier. That was in a different cave, just 10 miles, away, also in the Cradle of Humankind. It was Lee's first big find.

LEE BERGER: The story all began on August the 1st, 2008, when I came into this valley, following targets, which were these trees above my head that I could see on Google Earth. I walked up that old lime miners' trackway, which wasn't quite as clear as it is today, mostly overgrown, and I came into this grove and found this little hole.

NARRATOR: The little valley was called Malapa. Lee thought he knew it well. It was a Friday. Lee's nine-year-old son, Matthew, and his dog, Tau, were with him.

LEE BERGER: I stood at the edge of this pit, and I said, “Go find fossils.” With that, Matthew raced off into the bush, here. I thought he was going to go chase giraffe or zebra or something like that, with Tau in tow. And a minute-and-a-half later he shouted, “Dad, I found a fossil.”

Sitting right over by that lightning-struck tree, he had stopped and found a little rock. And I almost didn't go and look, because I knew he had found an antelope fossil, because that is pretty much all we ever find.

LEE BERGER'S SON, AGE 9: I saw a fossil. I didn't think it was a hominin, I just thought it was an antelope, 'cause we find thousands of those.

LEE BERGER: I started walking towards him, though, because I had to see what he had found, and five meters away, I realized that, sticking out of that rock, was a hominin clavicle. I couldn't believe it.

I took the rock in my hand, and I was turning it, trying to think what else this could be. And as I turned the back of it over, there, sticking out of the back, was a mandible and a canine. That's when I realized that an extraordinary thing had taken place.

NARRATOR: After almost 20 years of searching in the Cradle of Humankind, Lee finally had a major discovery. He had his son to thank but, also, a crew of Welsh miners, who had come through the valley a hundred years ago.

LEE BERGER: And they'd come through this area looking for limestone to build Johannesburg. And they would blast these caves apart, looking for that rich, white, pure limestone. And they'd burn it and make cement out of it.

NARRATOR: In the 1880s Johannesburg was a gold-rush town, little more than a collection of shacks. But it sat on some of the richest gold seams ever discovered. As the gold kept coming, so did the gold prospectors. The town grew, and construction crews were desperate for limestone, essential for cement and gold processing. Lime miners combed the high veld outside the town looking for seams of limestone.

Although they likely didn't know it, these seams concealed remnants of ancient cave systems and were full of fossils. When they found the limestone seam at Malapa, they laid their charges as usual.

LEE BERGER: They came in here and put in three, at the most four blasts. One right below me here, one over on the side, one over there that I can see.

NARRATOR: Then, for some reason, the miners never collected the blocks of lime and left the blast hole largely untouched.

LEE BERGER: I'm not sure why they did that, but what they did do in that process was expose just the edge of these remarkable skeletons. They damaged it just enough so we could find this site, and could make these fossil discoveries, but not too much that they destroyed the evidence. It really is a miracle.

NARRATOR: It was in one of the rocks scattered by the blast that Matthew found the collarbone of a child. But that was just the beginning. The hole where the miners planted the dynamite would soon yield so much more.

LEE BERGER: It was only once I had the permit, and we came back on September 4th, a whole bunch of us, that we spent all morning looking here and we found nothing. We were even thinking of leaving, 'cause we thought that there wasn't anything here. I stood over on the other side of this pit, looking down into that pit, and I saw something sticking out of the rock right down here.

And what I saw stunned me. I climbed down the pit and looked right over here and there, sticking out of the wall, was the proximal humerus of a hominin. I couldn't believe it. I did my Ph.D. on this. I climbed closer, and, as I got closer, I realized there was a scapula of the shoulder blade in place. And I came even closer and put my hand on the wall, right here, and two hominin teeth fell into my hand. Then I said something, and that started the second part of this remarkable story. Everyone piled down in here. At my feet was a proximal femur, in a block, here, that clearly belonged to the child.

What was amazing was it never crossed my mind that this wasn't the child that Matthew had found. How could you find two skeletons in a site like this? What it would turn out to be, of course, was a second skeleton, the female skeleton. The child would be laying right here, just lying in position here, and it would turn out that there were other skeletons here. There was one sitting over there. There's a baby just above me here, and who knows how many are in front of me here. It really is a treasure trove of paleoanthropology.

NARRATOR: One by one, they took out blocks of stone they thought might have hominin fossils in them, remnants of our ancient human family. The blocks were all taken back to the University of the Witwatersrand.

At the medical school, Lee's wife, Jackie, a radiologist, ran the blocks through a C.T. scanner, allowing the scientists to peer inside.

C.T. TECHNICIAN: Higher. There we go. Okay. That's good. Yep.

NARRATOR: What one of those blocks revealed was stunning.

LEE BERGER: A slice came through, and you could see an entire skull. I was dumbfounded. I could not, in my wildest dreams, believe an entire skull could be sitting in this little rock.

NARRATOR: Then began the painstaking job of freeing the skull from the rock that had encased it for possibly millions of years.

CELESTE YATES (University of the Witwatersrand): It took me three months to get it out. I was the first one that saw this. And you can't describe this to anybody. It's beautiful. I mean it's been in the ground for 1.9-million years, and you're the first person to see that. I thought, “Well, you're beautiful.” I basically brought this boy back to life.

NARRATOR: Finally, the skull was free. Its small brain and forward projecting face made it clear that it was an Australopith, but details of the teeth and other parts of the skeleton made it unlike any found before.

Many types of Australopithecus once walked the earth, between about 2-and 4,000,000 years ago. Lucy is known as afarensis. There's also Australopithecus africanus. This appeared to be an entirely new species. Lee called it “Australopithecus sediba,” after the waterhole near which it was found in South Africa. In the local language, Sotho, sediba means “wellspring.”

The team was able to radioactively date the limestone layers in the cave with great precision. The layer containing the sediba skeletons was 1.97-million years old. That makes these creatures among the last of their kind, living right at the end of the fossil gap between Australopiths and Homo erectus.

Here, at last, was a creature that could tell us something about that transition. And the bones were not just fragments. Here were two remarkably complete skeletons, a female and a child.

Still encased in the rock at Malapa, are fragments of at least three more, waiting to be excavated. This made sediba the most complete evidence ever found, for what was going on at the dawn of humanity.

CAROL WARD: The Australopithecus sediba fossils are some of the most spectacular skeletons known for early hominins. They're absolutely amazing. We don't get two bones associated with one another very often, much less several bones, much less partial skeletons. So that makes these fossils really special.

STEVE CHURCHILL: Sediba was exciting from the get-go. Right away, we knew that we had parts of the skeleton. And we had parts of the cranium, which helps us figure out who this animal is. So, that was really, really exciting. And, initially, these upper limb bones looked very primitive. So, we knew we were dealing with something that looked like it would be a good climber, kind of an ape-like creature.

NARRATOR: Peter Schmid's job is to reconstruct sediba's skeleton. Unlike past fossil finds, here, the skeletons are so complete, there doesn't have to be much guesswork. By scanning and mirror imaging, Peter can fill in any missing bones, with great accuracy.

PETER SCHMID: From the C.T., we've got a few thousand slices now, and Aurore has to put everything together to form a 3D model. And then we have to cut the model, because the pelvis we already casted, so, we only need the ribcage. But the right ribcage we have already, but we need now the mirror image of that, and the computer helps us to do the mirror image in a second.

NARRATOR: Layer by layer, a 3D printer then slowly prints the ribcage in fine plaster.

PETER SCHMID: Beautiful.

NARRATOR: Finally, Peter has assembled a complete skeleton.

It is highly unusual. All Australopiths are a mix of ape and human, but sediba has a unique mosaic of features scientists have never seen before, in the same creature.

PETER SCHMID: The arm is very long, like in a chimpanzee, but the hand is with short fingers and very long thumb, like a human hand, which was never found, until now, because this is the most complete hand ever found in this period.

NARRATOR: Job Kibii, who was with Lee and Matthew when they discovered the skeletons, has been working on the sediba hand. He's found an unusual combination of ape and human features here, too.

JOB KIBII (University of the Witwatersrand): What's special about sediba's arm and hand is that we know that sediba has a very long thumb, which is more chimp-like, but sediba has a very human-like hand. For example, sediba has a thumb which is longer relative to the other fingers, which indicates a human-like condition.

NARRATOR: Sediba's hand, with its opposable thumb and forefingers, is so human that it could've been a tool user. But since no tools were found, that remains only an intriguing possibility.

From the reconstructed skeleton, paleo-artist Viktor Deak can start to create a lifelike digital painting. By virtually applying tissue thickness markers, carefully calculated from the known facial tissues of living primates, he can build up a realistic impression of sediba's face.

VIKTOR DEAK: Once that was all done, I have now gone ahead and created a body for it. And if you want to see, we can check all that by going transparent, and seeing, making sure that the bones and everything line up in the proper spaces. So, here we have a concept reconstruction of how sediba potentially could look like.

NARRATOR: The step from there to a lifelike digital painting is a short one. Finally, for the first time in almost 2,000,000 years, the face of Australopithecus sediba looks out on the world, once again.

But the true revelations will come from the bones themselves. Because they are so well-preserved, these fossils will give scientists unprecedented insights into the lives of these ancient creatures, everything from what they ate to how they died.

Such details might help explain the Australopiths' transition into our genus, Homo. They might also prove or disprove a highly influential theory about the dawn of humanity, a theory inspired by the very first discovery of an Australopith fossil.

The year is 1924. Anatomist Raymond Dart teaches at the University of the Witwatersrand, in Johannesburg. His hobby is fossil hunting, but he never imagines he will find a human ancestor. Nobody, at the time, believes we had evolved in Africa.

RICK POTTS: Well, in the late 19th century, fossils were found in Europe, with the Neanderthals; they were found in Asia, with the earliest known examples of Homo erectus. No one really had a sense that anything interesting occurred in Africa.

WILLIAM HARCOURT-SMITH (American Museum of Natural History): Darwin and Huxley predicted that our origins would be in Africa, based on comparative anatomy. You know, they looked at the skeletons of chimps and gorillas, and they looked at ours, and they went, “Well, they're so close to us, and they're more close than anything else, so it must have been in Africa.” And then the, sort of, second generation of evolutionary biologists shied away from that. They started to find fossils in Europe; they started to find fossils in Asia. And, of course, that tied in very nicely with sort of racist and imperialistic thoughts of the day: they couldn't abide the thought of it being in Africa.

NARRATOR: In late 1924, Raymond Dart receives a package. He sees it's from the mining town of Taung, in South Africa's North West province.

RICK POTTS: And in that box is a fossil. And this is a game-changing fossil.

NARRATOR: It has been sent to him by miners who noticed what looks like the skull of a small ape encased in the rock. Dart is fascinated. He begins the long laborious process of revealing the mysterious skull. He can see that it is the skull of a child, but like no child he has ever seen before. It has ape-like characteristics but also some very human ones.

RICK POTTS: And so, as he cleaned this fossil, and he saw the hole in the bottom of the skull, where the spinal cord enters the brain underneath, that he had something like a two-legged walker on his hands. And this he named Australopithecus africanus, and what that means is “southern human of Africa.”

NARRATOR: Dart rushed into print with his find. He claimed it was proof that we evolved in Africa, just as Darwin had predicted. He was unprepared for the firestorm his theory unleashed.

DON JOHANSON: The Taung child sparked an incredible revolution. Up to that point everyone said, “Let's look to Europe for our ancestors.” It was unthinkable that anything as important as the emergence of humans could have happened in Africa.

ZERAY ALEMSEGED: Raymond Dart was a feisty guy, and when he was pushed back by the British intelligentsia, he became feistier, more aggressive, in terms of his defending of his views.

WILL SMITH: Most scientists disagreed with him. He really was seen as an outsider, but it absolutely set the ball rolling for one, paleoanthropology, as a field, in Africa and two, vindication of what Darwin and Huxley had predicted, with actual fossil evidence. It showed, once and for all, that our origins were in Africa and only in Africa. And that's huge. It totally changed the field.

NARRATOR: Dart was sure he had discovered the missing link between apes and humans. But it wasn't enough to know what they looked like. He wanted to know how they behaved. What sort of creatures were they? He understood that these great questions about our ancestors were also questions about ourselves.

LEE BERGER: The reason we are interested in our own ancestry, I think, is the reason that you or I want to know who our parents were and who our grandparents were and who our great grandparents were, because, somewhere in us, we realize that there's a little bit of them in us. So, to understand the quirks of our own behavior and why we do things, if not just why we look the way we do, comes from that ancestry. Paleoanthropology is just that, in deep time. We're looking way back. And so we're looking at the things, the, sort of, little bits and pieces that drive why humanity is like it is today.

NARRATOR: Raymond Dart was building a theory about how the Australopiths, our ape-like ancestors, became human. His ideas about the dawn of humanity were the touchstone for thinking about our origins for generations.

RICK POTTS: In the 1940s, more examples of Australopithecus began to be found. And a key site not only had fragments of Australopithecus, but also the bones of many other fossil animals. And Dart noted that these bones were broken in a special way.

NARRATOR: Dart became convinced they were weapons made by our primitive ancestors. Was this the key to what first made us human? Dart had been a young medic in World War I. He had seen, firsthand, the barbarity humans are capable of. It made sense to him that the origins of humanity were steeped in blood.

BRIAN RICHMOND: Raymond Dart's experiences in the world war may have colored his interpretation of what these bones and teeth meant. You know, it gave him a view of the dark side of humanity and the violence of humanity, and he came up with this idea that Australopithecus had figured out that bones and teeth were hard and could be used as weapons to kill other animals, the, sort of, “killer ape” theory of early humans.

NARRATOR: Dart believed that the more aggressive and adventurous of our ape-like ancestors abandoned their forest environments and moved into savannahs. There, they became hunters and predators. His theory that this violent transformation gave rise to humanity soon found an audience far beyond the small world of paleoanthropology.

RICK POTTS: In the 1950s, there was a drama critic and playwright named Robert Ardrey, who became very interested in human origins, and he went to Africa and spoke with Raymond Dart. And Robert Ardrey, being a dramatist, could write like anything, and he wrote this amazing book, published in 1961, called African Genesis.

NARRATOR: African Genesis became a pop science publishing sensation of the early 1960s. Ardrey's ideas, building on those of Raymond Dart, helped frame public debate about the dawn of humanity for the next 20 years.

RICK POTTS: The very first sentence in that book, I remember, 'cause I read it as a teenager and was enthralled by it: “Not in innocence and not in Asia was mankind born.” And, in that one sentence, he encapsulated Raymond Dart's ideas that it was an African genesis and that where we came from was not from an innocent creature but from the most violent of killer apes.

NARRATOR: One of Robert Ardrey's greatest fans was the filmmaker Stanley Kubrick. At the time he was planning a film based on the science fiction novel, 2001: A Space Odyssey. It was to be a meditation on human technology run wild. On a mission to Jupiter, the spacecraft's computer turns on the crew.

At the beginning of the film, our ancestors discover the first technology, weapons. Eventually, they will use them on each other. This was the "dawn of humanity" imagined by Dart and Ardrey.

RICK POTTS: And so, this sets up, then, for Kubrick, the same conflict that Dart felt. For Dart, that first weapon explained the emergence of human beings, while at the same time it explained the atrocities of the 20th century.

NARRATOR: Are we killer apes at heart? Is this what we will discover about our ancestors at the dawn of humanity?

The discoveries at Malapa may finally provide evidence to support or refute Raymond Dart's theory. The sediba skeletons are so well-preserved, they give the scientists a unique glimpse into their lives.

LEE BERGER: And that's the story we are really after: how did these individuals really live, out there, in the environment? What did they do on a daily basis?

NARRATOR: Whether they were so-called “killer apes” or not can be seen in what they ate. The first direct evidence comes from their teeth. At the Max Planck Institute, in Leipzig, Amanda Henry is analyzing calculus, or tartar, fossilized along with sediba's teeth.

AMANDA HENRY (Max Planck Institute for Evolutionary Anthropology): Calculus is what happens when the bacteria in your mouth form a film on your teeth. So, it's this very thick, layered, heavily mineralized material that forms around your gum line and all sorts of surfaces of your tooth. And as it forms, it traps bacteria and proteins and remnants of your food inside.

NARRATOR: Just like the tartar dentists remove from our teeth, the calculus from sediba's teeth provides a snapshot of what they were eating.

AMANDA HENRY: So, once I have the calculus here, in this little powdered form, I'm going to dissolve it in a little bit of a weak acid. And then we're going to rinse that acid off, and hopefully, what we'll be left with is micro-remains, with this mineral matrix removed. And then we'll look at that under a microscope and see if we can identify what was in the calculus.

NARRATOR: Amanda can see what sediba was eating, when she discovers phytoliths, the microscopic remains of plants.

AMANDA HENRY: Well, this is a phytolith that we recovered from the calculus of the sediba individuals. And we have a couple of examples here, all from different plants that this individual ate.

NARRATOR: Here, at last, is evidence that will help support or disprove Dart's theory.

AMANDA HENRY: Well, this is the first time that we've had direct evidence of the kinds of foods that any Australopith ate. We've had proxy information before, we've had sort of vague categories, where the food's harder or tougher, but this is direct evidence. That's exciting.

NARRATOR: What Amanda can see trapped in sediba's tartar are microscopic remains of many different plants.

AMANDA HENRY: We have phytoliths from grasses, we have phytoliths from the bark or woody tissue of plants, and we have phytoliths, possibly, from fruits. So, all the evidence suggests that the foods that this individual was eating was coming from closed-forested regions, so eating fruits, maybe chewing on stems, eating the grasses that are growing in that area.

NARRATOR: The tooth evidence from sediba indicates a diet very similar to today's chimpanzees. While they may have eaten some meat, there's little to back up Raymond Dart's theory that they were killer apes.

BRIAN RICHMOND: So later, scientists came and looked at the evidence and found that there were tooth marks in the skull of an Australopithecus individual. And that was just really compelling evidence that Australopithecus, maybe, instead of being the predator, was the prey.

ZERAY ALEMSEGED: So our ancestors, or the early hominins in South Africa, were the victims, rather than being the carnivores that Raymond Dart wanted them to be. The caves in which he was finding, not only the remains of human ancestors, but the remains of many, many, many other animals, which he thought were being consumed and devoured by our ancestors, were actually all the victims of predators and carnivores, who were pulling all of those animals into the cave.

NARRATOR: It seems Raymond Dart's vision of our ancestors as the first killer apes, so famously portrayed by Stanley Kubrick, was wrong.

The sediba skeletons are so well-preserved, they offer the team a chance to investigate, not just the lives, but the deaths of these individuals. They can analyze the 2,000,000-year-old death scene, almost as if it were a forensic case.

LEE BERGER: I mean, we're looking at the preservation of organic material here. These animals are articulated the way they died. The breakage patterns may often be a result of the moments before or shortly after their death.

NARRATOR: So far, the team has excavated the skeletons of a female adult and a child.

AURORE VAL (University of the Witswatersrand): So the female was this one, and the juvenile is all the bones in blue, all of these. They were found very close to each other.

NARRATOR: Aurore Val has been creating a virtual reconstruction of the scene at the bottom of the cave. Besides the sediba skeletons, there are the skeletons of many other animals too. How did they all get there?

Two-million years ago, Malapa was a much deeper cave. Landscape erosion has reduced it to a small depression in the ground. But when Australopithecus sediba was around, it was a cave system about 90 feet, deep.

LEE BERGER: Imagine a vertical shaft going up, there is probably water dripping down, roots hanging down. Right here is the curled up body of the female. Lying right there is a child's body, the 13-year-old boy. There are other animals, all being eaten by bugs and going through the usual process of decay.

NARRATOR: This reconstruction shows the sediba death scene in great detail. Now the team want to know how all these creatures died. Were they dragged in by predators or did they fall?

The man to answer that question is Patrick Randolph-Quinney. He's an eminent forensic anthropologist more accustomed to working on murder cases and mass graves.

PATRICK RANDOLPH-QUINNEY (University of the Witwatersrand):I'm involved in looking at homicides, and I'm involved in looking at the forensic identification process, so, unknown remains, giving them back their identity and their name, that's what I do for a living.

NARRATOR: The skull of the child is the first piece of evidence.

PATRICK RANDOLPH-QUINNEY: This is this fracture, here. And it is a fracture that has actually separated part of the body of the jaw, and it runs up through the tooth. And, basically, if you are in an impact, you jar your teeth together and you create compression on the tooth row, and that provides force, or generates force, which goes down to the tooth roots. And what this has done is actually split part of the corpus apart. So it's actually damage consistent with, effectively, an impact on the jaw, and the energy has come from the teeth out into the bone around it. And that only happens mechanically with fresh bone, so this individual was still functioning skeletally when this happened.

NARRATOR: The mandible fracture is a green fracture that happened when the bone was fresh, at or around death. It would be consistent with a fatal fall. The fractures to the forearms are even more telling.

PATRICK RANDOLPH-QUINNEY: And if you look at MH2, she's got a fracture that runs through the body of this joint, where it articulates in the elbow with the humerus, the bone of the upper arm. There are also fractures associated with the wrist, in this portion of the ulna and this portion of the radius. And we've actually got fractures in the scaphoid and triquetral bones in the wrist, as well. And what this appears to indicate is putting your hand out to stop yourself.

NARRATOR: This seems to be good evidence the individual was alive when she fell. The cave at Malapa was probably a death trap. Were they searching for water and lost their grip? Perhaps they were trying to escape in terror from some predator. Whatever the reason, they fell and died either immediately on impact or soon after.

It appears that mud then buried the bodies and as it hardened, kept them from disintegrating. This is why they were so well-preserved. Then began the long slow process of fossilization, in which all organic material in the bone was replaced by minerals.

Today, the sediba fossils are still yielding insights into the Australopith world of almost 2,000,000 years ago. But the most tantalizing question of all is still unanswered. How did these primitive creatures evolve into more advanced human ancestors?

To find out, scientists need to find perhaps the most elusive fossils of all, the first members of our genus Homo. For decades the only fossils that came close were the fragmentary remains of a creature called Homo habilis: handy man.

RICK POTTS: In the early 1960s, fossils discovered from Olduvai Gorge, in Tanzania, by the Leakeys, led to the definition of a new fossil species in our evolutionary tree, Homo habilis, handy man. And what was significant about that is that stone tools were connected with what Leakey proposed as the first human, a member of our lineage, the genus Homo.

NARRATOR: Like most scientists at the time, Louis Leakey thought our evolution was probably a gradual, linear process, a single chain of species becoming progressively more human. He decided the key event that made our ancestors cross the threshold to humanity was not the invention of weapons, as Raymond Dart believed, but tools.

Since Homo habilis seemed to be the first toolmaker, he declared it the first member of our genus: Homo. Here, at last, was the link between the ape-world of the Australopiths and the human world of Homo erectus.

WILL SMITH: So, there was always this gap between Australopithecus and later members of the genus Homo, like Homo erectus and Neanderthals, and we didn't really know what species in that gap would've looked like. And then, along in the 1960s, along comes along Homo habilis. And it's slightly bigger-brained, it's probably a bit more bipedal, and of course it had these stone tools associated with it. And it was argued very strongly to be a contender for early Homo, and it was instantly controversial. And it's still controversial to some people, today. It's a bit of a mess.

LEE BERGER: Because it became clear, probably in the 1990s, and moving into the early 21st century that Homo habilis, we really didn't know what that was.

NARRATOR: One of the main reasons for classifying it as human was that it was found with tools. But that is now looking less like a defining characteristic of the genus, Homo. We now know that even the primitive Australopiths had the capacity to use stone tools.

Zeray Alemseged, who discovered a 3,000,000-year-old Australopith called Dikika child, has found what he believes to be evidence of stone tool use in the same period.

ZERAY ALEMSEGED: If you were defining Homo habilis as a toolmaker, tool user, then what do you make of it when you see that Australopithecus was doing the same thing?

DON JOHANSON: We know that there is rudimentary stone tool use, not stone tool, but stone use, among living chimpanzees.

NARRATOR: The confusion surrounding Homo habilis has grown. It has been compounded by the fact that so little of it has ever been found.

LEE BERGER: Colleagues have said, “You know, if you had a shoebox, you could put all those fossils that might be early members of the genus Homo into it and still have room for a good pair of shoes.”

NARRATOR: With so few fossils to go on, scientists had little they could say for sure about the first members of our genus, Homo. This was the situation when the two young cavers, Rick Hunter and Steven Tucker, made their discoveries in the Rising Star cave.

When Lee saw the photos from the fossil chamber, he could only hope they would clear up the confusion. Was it another sediba or was it even Homo habilis? The only way to find out was to bring up the fossils. Lee knew there was no time to waste.

LEE BERGER: I had to make a decision, and about, oh, just before one a.m., I decided that history would never forgive me, if I did not act right then.

NARRATOR: Just five weeks later, the Rising Star excavation was beginning to take shape. It's planning had taken some ingenuity. Lee knew he would never be able to get down to the fossil chamber himself. In places the chamber entrance was less than seven inches wide.

LEE BERGER: I put a call out on Facebook, saying I need skinny scientists who are not claustrophobic, who are cooperative, who can work together in a dangerous and difficult environment. And I need you available by the first of November.

HANNAH MORRIS (Chena Consulting Group): I saw Lee's Facebook post, actually, and, on a whim, I applied for it. And then, the next thing I know, I got asked to an interview, and from there, just things started happening really quickly.

K. LINDSAY HUNTER (Sepela Field Programs): I saw a call that came out on Facebook, from Lee, that was looking for skinny scientists, skinny paleoanthropologists that weren't claustrophobic and that would be able to fit into a slot that was about 18 centimeters. And that was very intriguing.

LEE BERGER: I didn't say what had been discovered. I didn't say anything about what I thought it was. They only knew it was me, in South Africa, and it was clearly underground. I thought I'd get three, four, five applicants. I really did. I mean, how many people in the world could be qualified and could fit that criteria? Within ten days I had 57 qualified applicants from all over the world, most of them women.

ALIA GURTOV (University of Wisconsin–Madison): One morning, I woke up and there was a call for tiny, experienced archaeologists, from Lee Berger, and I thought, “That's me.”

BECCA PEIXOTTO (American University): I received the Facebook post via a friend, who saw that it was an ad for small archaeologist with caving and climbing experience, and she said, “That's you!”

MARINA ELLIOTT (Simon Fraser University): I'm almost finishing a Ph.D. in physical anthropology, osteology, so this is my area.

BECCA PEIXOTTO: I'm an archaeologist, so I can study up quick on the paleo stuff.

ELEN FEUERRIEGEL (Australian National University): I'm a Ph.D. candidate, specializing in evolutionary biomechanics, so, more on the paleo-anthropological side of things.

MARINA ELLIOTT: It really seemed perfect. In fact, when I read the callout to my husband he said, “Well, they might as well have meant, you know, written, ‘Marina is wanted over here.'”

NARRATOR: The Rising Star expedition was to be a new kind of paleoanthropology, tailor-made for the age of social media and the Internet.

LEE BERGER: I held Skype interviews, and I did a few things in that, with the 11 people that I short-listed out of this spectacular list of applicants.

ALIA GURTOV: Lee explained a little bit about how the cave was found and shared with us some video footage and the initial photographs that Steve and Rick took. And he told us about the conditions of traveling into the cave. So, you know, he wanted to make sure that we really knew what we were getting into.

ELEN FEUERRIEGEL: It was mysterious. It was very enticing for that reason, you know, sort of wondering what sort of circumstances there were that necessitated asking for small people with excellent paleontological skills.

LEE BERGER: In the Skype interviews, I wanted to see these people face to face, but I also wanted to test some things. I needed to know that if I shut the cameras off, which I did for many of them, I wanted to hear if they could respond to me, because I had already designed, by then, this system of communication. I knew, I knew I was never going. I will never set foot in that chamber.

MARINA ELLIOTT: Then maybe a day after that I was told I was a go. It was so fast, so fast.

LEE BERGER: And I sent off emails saying, “Congratulations. Pack your bags. Expect to be here in the first week of November.

LINDSAY HUNTER: Then I got the email that said that I got it, and then, characteristically, I bust out crying and just kept reloading my email to make sure, refreshing it, just like, “Really, it's really there. It's really there.” And I screamed so loud.

BECCA PEIXOTTO: It was a very quick process. The ad went up, and then the interviews happened the next week, and then I learned a day later that I was accepted to the project. All of a sudden, I was rearranging my schedule and waiting for the plane tickets and packing up and reading, quickly, everything that I needed to know. It was fast and furious getting ready for this.

LINDSAY HUNTER: My brain was just like a flurry, an explosion of glitter and confetti. It's everything, it's like every best birthday and Christmas and Hanukah and Kwanzaa, and it's everything, all at once.

ALIA GURTOV: I figured, if he thought I could do it, if Lee thought I could do it, then I could do it.

LEE BERGER: I had no illusions that this was going to be easy. Nothing like this had ever been done, certainly in the African context, I knew, perhaps ever, anywhere. And I knew I had to have everything, from medical support, to safety support, to design of the infrastructure underground and above ground, and all the things that go on with a scientific expedition.

MAN: Let's get a bag.

NARRATOR: As the camp was set up, Pedro, Rick and Steve readied the cave for the excavators. Safety lines, lights, cables and cameras were installed. The possibility for accidents was ever-present. Lee rehearsed safety procedures over and over again.

LEE BERGER: Critical issue is, “No one panic.”

NARRATOR: A command post was set up from which he could watch virtually every part of the cave.

LEE BERGER: I really began to get a feel for what I was putting these young women into, as the cavers who were laying over two kilometers of cable. And I think they were terrified, and I was terrified. They were still untested. We took them through the caves, testing their capabilities in this system. And so, we reached the 10th, which was my intended day of going in, and we tested systems, everything worked. It was a little sloppy, but it worked. We tested safety. It all worked, and, by the early afternoon, we were ready.

PEDRO BOSHOFF: You'd be surprised, I'm actually a gentle soul.

NARRATOR: Marina, Becca and Hannah have been chosen to go down first. Still, nobody knows exactly what they will find.

LEE BERGER: I've seen a skull, I've seen the other pieces. I am pretty sure that we have got quite a lot of a skeleton of at least one hominin. That, of course, waits to be seen. And it's going to happen pretty fast now, over the next several hours.

NARRATOR: Anxiously watched by Lee and the team in the command post, Marina, Becca and Hannah make their way deeper and deeper underground.

MARINA ELLIOTT: The descent is difficult. And as I looked down there I thought, oh you know, “I don't know if I'm, if I can do this.” But then, once I was committed to go down, it was actually much, much easier than I was dreading.

I'm just trying to also slow it down a bit, because I've got the GoPro running.

HANNAH MORRIS: It was just an amazing, an amazing feeling, to realize how far away you are from everyone up top in the command center, and to just fully realize what you are down there to do. I became a little bit overwhelmed, but then you also have to turn that off, in some sense, because you're only down there for a little amount of time, and you have a job to do, a very important job to do.

BECCA PEIXOTTO: Going down the chute for the first time was, honestly, it wasn't as bad as I thought it was going to be. And then you come into a landing zone, and there's a hallway to pass through. It's not really a squeeze, but it's a narrow passage to pass through, and then the chamber opens up again.

MARINA ELLIOTT: This is the entrance to the cave, here. So, you start by descending down, you know, a fairly narrow shaft and some tunnels. You get down to an area, here. This is what we call the Superman crawl, which is a very narrow crawl, you have to crawl on your stomach for about three meters. Then you enter into another chamber. This is what we call the Dragon's Back, so that's the ridge climb with the sort of four- or five-meter drop on either side. You get up to the top of Dragon's Back, and you end up at the top of the chute, which is the, another sort of tunnel access, that, then, you start the 12-meter descent into the chamber. So, that's this area here. Once you drop into the chamber, you're actually just in a landing zone. It's another sort of antechamber. You then go through another passageway into the main chamber, which we call UW-101, or the fossil chamber.

NARRATOR: Marina is the first to enter the chamber.

MARINA ELLIOTT: There was a little bit of trepidation, I have to confess, and a lot of excitement, to be the first of the advance scientists to go into the cave. The first thing that came through my mind, when I went through the final slot into the actual final chamber was Howard Carter's anecdote about opening Tutankhamen's tomb. I think it was Lord Carnarvon in the back saying, “What do you see?” And Carter says, “Things, wonderful things.” And it was that feeling.

God this place is beautiful.

First of all, the cave is beautiful, just geologically beautiful, and then you look down and there was just a sea of bone, and it was obviously just not regular bone. Yeah, it was amazing, amazing.

LEE BERGER: And then I saw them enter this chamber. We got the cameras set up and you could see their feet moving. And it was surreal.

Fantastic! There we go. Skull is being flagged. You can see the skull here. She's now flagging the mandible.

And then the process started. The process of doing science began.

MARINA ELLIOTT: So, we'll put pin number one right beside the mandible, and that's where we'll concentrate. Okay, okay, das ist super. Okay, thanks. Bye.

CONVERSATION AMONG CAVERS: Yeah, that's perfect right there.

Okay, going to start scanning.

Okay, scan.

NARRATOR: The first foray into the fossil chamber lasts only a few hours. Enough time to start scanning and flagging bone fragments, as well as to test the safety systems.

CONVERSATION AMONG CAVERS: Good.

Okay, how did that go?

Let's see.

It's mapping right now.

NARRATOR: Finally, it is time to bring up the first precious fossil, the mandible.

LEE BERGER: There, their coming. I see what looks like a mandible in the middle there, on the right. That looks fantastic.

NARRATOR: It's Becca who will take care of it on the ascent.

MAN: All right!

LEE BERGER: You got the fossil?

BECCA PEIXOTTO: Yes, I got the fossil.

LEE BERGER: Well done.

BECCA PEIXOTTO: Here you go.

MAN: And we have everyone else.

LEE BERGER: Everyone's out. Rick's out safe. They're all out. Well done.

And so, first their safety, in that they were out was just this enormous emotive relief, and then the sense that they had actually got this thing, and now, I was going to see, for the first time, what all of this was about.

When they opened that little box and we unwrapped this thing that they collected, every great idea we had went out the window, gone, you know? Suddenly, we didn't know what we had.

NARRATOR: When he had first seen the jawbone in Rick and Steve's photos, Lee had decided it probably belonged to an Australopith. One of the most striking characteristics of an Australopith's face is its large ape-like jaws and teeth. As the Australopiths transitioned into the genus Homo, their faces shrunk. Jaws and teeth became smaller. When he finally had the jawbone in his hands, Lee saw it was too small to be an Australopith. It seemed quite human.

Could it be a new specimen of Homo habilis? Or could it be a new transitional species between Australopiths and early Homo? These are the questions on anatomist Peter Schmid's mind as he studies the mandible from Rising Star.

PETER SCHMID: We have this molar teeth and this very strange use of the frontal part, here, and, luckily, we got another piece. So, with these two pieces, we have a mandible, which is complete, and then we can put on the mirror image, and we have sort of outline.

NARRATOR: Peter can then compare it to the mandible of Homo habilis.

PETER SCHMID: I will take this away, and you see this is the tooth row of Homo habilis. You see, also, that these are massive teeth. But the tooth row is straight, and we have a very strong shelf here.

NARRATOR: The mandible from Rising Star is clearly more curved. It's not Homo habilis and it is not an Australopith. They don't know what it is.

DARRYL DE RUITER (Texas A&M University): This is pure confusion. We don't know what to make of it. We realize all of our preconceived notions have to be tossed aside. We can't go into this thinking this is going to belong in this group or belong in that group. We just have to start from, literally, scratch.

NARRATOR: The team hopes that as more fossils emerge from the cave, the confusion will clear up. There is reason to be optimistic. Each descent reveals more bones. Where once they thought there might be one individual, they now see evidence of a whole lot more.

LEE BERGER: It was probably a couple of hours into the first day, when we realized it also wasn't one skeleton.

MAN: Another femur.

LEE BERGER: If I remember right, it started with a second femur from the same side. And since there has never been a three-legged hominine, we knew there were two, and then there were three. And I think it was by day two, there were four. And we realized we were in something very, very, very special.

All right, good luck with that, Becca. We can't wait to see you. You've got something we want to see.

NARRATOR: Every time the scientists in the cave remove a piece of bone, they find more bones beneath it.

LINDSAY HUNTER: It's everywhere. I mean, it's all strewn, all throughout.

NARRATOR: Not just the chamber, but the passages leading to it are littered with bone fragments.

LEE BERGER: At the landing zone, where they stopped, I'd get a call on the intercom. We found another tooth.

RICK HUNTER: It was just sitting there. I was trying to find a nice place to sit, and there it is. It just caught my eye.

LEE BERGER: Rick was sitting there, as the safety caver, waiting, and he kicked the dirt and hominids fell out.

ELEN FEUERRIEGEL: You have to pass me up some flags.

RICK HUNTER: Do you have enough flags?

LEE BERGER: By the afternoon of day 14 in the expedition, we were overwhelmed. I'd started with one safe to hold one skeleton, day three we had two safes, day four we had three safes, day six, people were going, “We need more safes.”

MARINA ELLIOTT: Two more. I don't know whether you should hug me for someone finding something in another spot.

LEE BERGER: By day 14, as we would get fossil after fossil, we were getting 40, 50, 60, 70 elements a day, all that was flashing through my mind, as I was doing that, was that famous scene in Jaws where Roy Scheider is chumming, and they hadn't yet seen the shark, and he's sitting there chumming, and all of a sudden this gigantic shark appears. And he goes, “We're going to need a bigger boat.” We're going to need a bigger safe. It's extraordinary.

STEVE CHURCHILL: I think this year, at Christmas, I'm just going to hang one of these instead of a stocking.

NARRATOR: As the fossils accumulate in ever-greater numbers, a picture of the creature of the Rising Star cave begins to emerge.

LEE BERGER: This is part of a juvenile pelvis.

NARRATOR: Thigh and hip bones tell them it was an upright-walking biped, but its gait was primitive. From what they can see of the exposed skull, it is small, not much bigger than a chimp's. But the teeth and jaws seem more advanced: Homo-like.

The team's excitement grows. It's beginning to look as if they have found another species from the dawn of humanity. But on which side of the Australopith-Homo divide will it fall? One of the key fossils that will tell them that is the skull. They are saving that until last.

CAVERS: Distance is perfect. And I can see marker two.

Record.

Recording.

NARRATOR: In the meantime, another extraordinary fact is becoming evident. There are no other animals in the cave. All the fossils are human ancestors. This is unheard of.

LEE BERGER: It was pretty surprising that something completely normal to every other excavation I have ever been in on the continent of Africa, every one I have ever heard of on the continent of Africa, wasn't happening here. We weren't getting anything else, other than hominins.

NARRATOR: When early hominins are discovered in caves, they are always found along with the bones of other animals that have either wandered in and died or been dragged there by predators.

LEE BERGER: They're mixed with antelopes, generally, in huge abundance. Then you get, the kind of percentages you see, depending on the circumstances, you see carnivores and other bits and pieces, and rodents, the stuff that accumulates when things die and are eaten and are dragged into caves.

NARRATOR: Apart from the bones of a solitary owl, there's not a single other animal in the Rising Star chamber, only hominins. So how did these creatures get in there?

The chamber is very inaccessible: deep in the dark zone of the cave and with no entrance other than the long, narrow chute. The team believes it likely was just as inaccessible two million years ago.

It is starting to look as if the bodies might have been intentionally placed there. Could this possibly be some sort of burial? There has never been evidence of anything like this linked to such a primitive-looking ancestor.

LEE BERGER: So, we have that looming in front of us and don't have an answer to it.

NARRATOR: Until now, the earliest known burials are from about 100,000 years ago, and a much more advanced form of early human.

The team does not have a date yet for the fossils of Rising Star, but it seems unthinkable that such a primitive-looking creature could be disposing of its dead. But that's what it looks like.

And the age ranges of the individuals are very similar to what archaeologists find in cemeteries.

LEE BERGER: At the early stages of this expedition, they look like a cemetery population: very young individuals and very old individuals and nothing in the middle so far. It doesn't mean we're not going to find it. That's what you find in a cemetery when you dig it up. Right now, it looks a lot like that. Will it hold out to be that? That will be a mystery I will want to see solved. And we're left with this conundrum of, you know, “Is what we are looking at…?” You don't, almost, want to say it out loud.

NARRATOR: It's a mystery with profound implications, but one that will require further analysis before anyone is willing to back it wholeheartedly.

The excavation is now approaching its third and final week. Perhaps the most important bone has been left until near the end: the skull. Its shape and the size of its brow ridges will be crucial in telling them whether the creature of Rising Star is Australopith or Homo: human.

LEE BERGER: We're going to go ahead and bite the bullet and take that skull out.

ELEN FEUERRIEGEL: Yes, yes, yes, yes, good, good.

If only because it gets it out of the way.

LEE BERGER: Not because you want it out to see it.

ELEN FEUERRIEGEL: Oh, I want it out. Trust me.

LEE BERGER: A couple of reasons we want to get it out. One, the skull can tell you a lot. It can tell you cranial capacity and start getting an idea of the shape of the skull. Is it Australopith-like and pinched in the front, or is it rounded more like a human, or is it something in between, does it have sagittal crest neck? We want to see that skull.

And, also, the skull was probably the most complex initial extraction. It is fragile, it's a thin piece of bone, and it could break apart. We need to know if we can get something like that out. And we need to get it out to see what is underneath it. Whether this was a skeleton or whether there were lots of individuals associated with each other. So there was all this tension, and it was a lot harder to extract than we thought.

Oh, I'm sure you'll find plenty. All right, stage on in after her. Good luck everyone. Have a blast.

ELEN FEUERRIEGEL: Thank you. Will do.

LEE BERGER: Alright. Let's get you something here. Go get them. Good luck. Happy hunting.

K. LINDSAY HUNTER: Thank you. Enjoy topside.

NARRATOR: The skull is extremely fragile. The team carefully scans the area immediately around it.

ELEN FEUERRIEGEL: How big?

K. LINDSAY HUNTER: That's perfect.

NARRATOR: Then they begin the laborious process of removing every tiny fragment of bone surrounding the skull.

K. LINDSAY HUNTER: Oh, we've got medium bags now.

NARRATOR: Finally, they delicately scrape away the dirt to release it.

LEE BERGER: Everyone was feeling all these points of tension around the science of the skull, when we knew it was imminent coming out. We only had two people down on the bottom, and they were working on it, Becca and Marina, and working and working and working, and finally, we kept trying to call them out, and they wouldn't come out, because they knew they were that close to the extraction. And, eventually, it did come out.

That's it. That's it. It's so fragile.

NARRATOR: With everyone holding their breath, praying that it does not break, the skull fragment is finally lifted and delicately placed in a box. Then it begins its slow ascent, leaving the cave, for the first time in possibly millions of years.

LEE BERGER: And he's holding the box.

JOHN HAWKS (University of Wisconsin–Madison): Yeah, that's right, he's holding the box. So he can't do this. He's got to be much more careful than that. There it is. All right.

MAN: How fantastic.

JOHN HAWKS: Wow.

LEE BERGER: And all of those scientists piled back in, all of the people that spent so much time and so much energy coming to this moment, went back in there, and they lined up in the most difficult places, up the Dragon Back to Base 1, and they knew there was a risk that it could get damaged. If dropped, it could get destroyed. And this huge team effort occurred as they handed this off from one to the other, as it moved its way from this dark recess, where it has been for however long it has been, to the entrance of the cave, where those of us not privileged enough to be able to get into this system had to wait with huge tension, watching this passage on the cameras until there it was.

LEE BERGER: There we go folks, let's go get it.

Great moment.

LINDSAY HUNTER: There is so much wonder. No one's bored. No one's too academic to hold it in. Everyone is just brimming with childlike excitement.

LEE BERGER: Would you hate me, if I took this before I hug you?

MARINA ELLIOTT: Please take it.

LEE BERGER: Oh, well done.

MARINA ELLIOTT: I don't even want to hug you with that thing in your hand.

LEE BERGER: I'm going to give this off to John.

ELEN FEUERRIEGEL: I am constantly sitting there and stopping myself and going, “Oh, my god. This is like, this is probably the first time this fossil has seen the light of the day in millions of years.” And so, I am continually sort of having to stop and just think for a moment and sort of revel in it.

NARRATOR: It's the moment everyone has been waiting for. They hope the skull fragment will be the telltale piece to identify the creature of Rising Star as either an Australopith or a member of our own genus.

LEE BERGER: Looking at a left frontal, so it's this part, the orbit and then part of the brain case behind the orbit. And that is a very important piece.

NARRATOR: Large orbital ridges with indentations behind them would indicate Australopith; smaller brow ridges with evidence of a more rounded skull would say Homo.

LEE BERGER: We do have our genus. We have our genus!

DARRYL DE RUITER: This is indisputably Homo.

CAVERS: Yes!

Yes!

NARRATOR: The team's verdict is clear: they have a new member of our genus. Now the question is: what can it tell them about the mysterious dawn of humanity?

LEE BERGER: We are certain that this is in the genus Homo, our genus, and we are certain it's a new species. And that's where we are right now: the idea that we've discovered a large number of individuals, males and females, young and old, of a new species in the genus Homo.

NARRATOR: In the next phase, they will have to piece together and analyze the rest of the fossil remains. Already they have almost 2,000 bone fragments from more than 12 individuals.

CAROL WARD: The Rising Star discovery is one of the most startling and amazing discoveries in all of hominin evolution. To have that many fossils in one place is unprecedented and took everybody by surprise.

NARRATOR: The excavation was planned as a three-week operation. As it nears its end, the scientists know they will have barely scratched the surface of what Rising Star has to offer.

LEE BERGER: I had never seen or dreamed of anything like the richness of this site. There aren't just hundreds of bones, there are thousands of bones. It's clear. You can't blow on the ground and it doesn't uncover another one. They can't gently brush their hand across it, and teeth and long bones don't fall out, usually of another individual. This is going to take a long, long, long time.

NARRATOR: As everybody goes home, the Rising Star fossils are carefully transported to the University of the Witwatersrand.

It was here, 90 years ago, that Raymond Dart sparked a firestorm by declaring that the dawn of humanity was in Africa. It seems fitting that it is here, too, that the mysterious early humans of Rising Star will begin to tell their story.

At a symposium, six months after the excavation, researchers meet for an intensive analysis of the fossil material.

LEE BERGER: They're in the analytical phase here, they're in the diagnostic phase, and it's been an experiment in working together, bringing together some of the brightest minds on the planet with some of the most current data sets, to analyze over 1,700 fossil hominin remains that we recovered only last November. And it's been fantastic to watch, this constant energy of science. And you can almost feel it in the room right now.

WILL SMITH: We are total nerds. It's nerd heaven here, but it is an extraordinary experience. There's never been anything like this before, in the field of hominin paleontology, to get a group of young, talented scholars together to bring their new techniques and their fresh outlooks, on the record, to newly discovered fossil hominin remains. This certainly never happened when I was a Ph.D. student, and I would have died to have done this.

NARRATOR: As the analysis goes on, the bones from the Rising Star cave are finally ready to be presented to the world.

LEE BERGER: We've got a new species of early human in the genus Homo, and that's tremendously exciting. We've never had anything in that transition period between the late Australopiths and the earliest members of our genus in any kind of abundance, and, boy, we have it in abundance now.

NARRATOR: To members of the team, the fossils suggest a creature unlike anything ever found before.

JOHN HAWKS: We're looking at creatures that are humanlike in their feet, humanlike in their hands, humanlike in their teeth, everything that interacts directly with the environment is Homo; and everything that is sort of central, the trunk, the architecture of the vertebral column, the brain, those sorts of things are more primitive. It's like evolution is crafting us from the outside in.

LEE BERGER: We've called the species Homo naledi, and “naledi” means star in Sotho. And we've called the chamber that the fossils come from—it still has fantastic fossils to be found—the “dinaledi” chamber, which means the chamber of stars.

NARRATOR: Homo naledi is a strange mosaic of ape and human, small-brained and small-bodied, with chimp-like arms, but with human hands, teeth, small brows and long legs, probably a long-distance walker.

LEE BERGER: Naledi is a surprise in very many ways. It's got an incredibly tiny brain. A brain that's more than a third as small as a modern human's brain is. Yet it's clear, when you look at the cranial shape, the dentition, the legs, particularly the feet and even the hands, that this thing is part of our genus.

NARRATOR: Here are creatures on the cusp of becoming human but still very close to the Australopith world. It makes the question of how they got into the cave even more intriguing.

JOHN HAWKS: It looks like they got in there because somebody put them there. Now, if we say that, you have to understand, that's a very controversial thing to say. And so, we approach it very conservatively. We can show that there's no signs of predation. We can show that there is no predator that accumulates only hominines in this way. We can show that they didn't all get there at once. We can show there is not a flow of material into the chamber, and that's where we leave it, scientifically. You know, we can say, the best hypothesis we can come up is, they were put there.

NARRATOR: If this is true, its implications are far-reaching. They now know that the Rising Star hominin had a brain size in the range between 450 and 550 cubic centimeters. That's just slightly larger than a chimp's.

STEVE CHURCHILL: So, if, in fact, the Rising Star hominins are purposefully disposing of their dead, we're talking about some small-brained hominins who are doing this. And that begins to change our thinking about, sort of, the cognitive attributes and the neural machinery that you need to engage in that kind of behavior. And that becomes really interesting.

NARRATOR: The accumulation of Homo naledi skeletons in the cave raises the type of big question that Raymond Dart wanted to answer. What type of creatures were our primitive ancestors? If the naledi skeletons have indeed been intentionally disposed of, some sort of burial, it would indicate already quite advanced social behavior.

This fits with new ways of thinking about the transition from ape to human. Many scientists now believe that a key element of that transition was the growth of ever-stronger cooperation and social bonds. Psychologist Michael Tomasello has spent a lifetime comparing the social behavior and capacities of chimpanzees and human children.

MICHAEL TOMASELLO (Max Planck Institute for Evolutionary Anthropology): Well, there's social and there's ultra-social. And all mammals are social to some degree. Great apes are especially social in the sense that they form long-term relationships with others, and have bonding relationships with others, and they groom and support each other in fights. So, they're very highly social creatures, but a lot of it is organized around competition. So, a lot of it is organized around coalitions to fight over food and so forth. And in humans we, of course, haven't lost our selfish and competitive streak, but we have become so much more cooperative, not perfectly cooperative, but much more cooperative.

LEE BERGER: The fact that we can sit in an airplane with 3- or 400 hundred individuals of breeding age that we aren't related to and not rip each other apart is a uniquely human character, and it was evolved on this landscape behind me, because Africa is a harsh place, and we, as early humans, had to evolve cooperation in order to survive here. We didn't have big canines and sharp claws, we just had each other.

NARRATOR: Humans are the most highly social primates ever to walk the earth. We bond and form relationships far more complex than any other primate.

So, if the Rising Star chamber is indeed a burial, perhaps this would suggest that here, at the dawn of humanity, those more complex social bonds had begun to take shape. This possibility will generate fierce debate as other scientists weigh in. But how do these discoveries change the narrative of human evolution?

STEVE CHURCHILL: There is an old refrain in paleoanthropology. People always say, “We need more fossils. We need more fossils. We need more fossils.” But, the fact of the matter is, more fossils just complicate the picture.

NARRATOR: One compelling question to be answered is: where do these new fossil ancestors fall on our family tree? Dating the fossils is proving to be difficult and complex. It will take time.

CAROL WARD: The thing that's hard about it is we don't know how old those fossils are, and we can tell what they look like because we have so many of them, but if they're 3,000 years old or if they are 3,000,000 years old, it's going to mean a very different thing for how it changes our understanding of human evolution.

NARRATOR: Because we have a date, things are a little clearer with the Malapa finds. At 1.97-million years old, most scientists believe sediba is too late to be a direct ancestor of ours. Our genus Homo was already established by the time sediba came along. But even if sediba is not our direct ancestor, it does show there were many different types of primitive ancestors living together at the same time.

MAN AT EXCAVATION: 'Kay. Yeah, yeah. Keep on.

ZERAY ALEMSEGED: The quality of the material that Lee is uncovering is really phenomenal. Sediba shows that we had more than two or three species in South Africa, 1.9 million years ago. It's a very interesting find. It shows that there were diversity. It's a beautiful material, but I don't think that sediba was ancestral to our genus Homo.

NARRATOR: Whether or not they are our direct ancestors, the fossils at Malapa and Rising Star point us toward a new way of thinking about human evolution.

STEVE CHURCHILL: We have a strong tendency to want to draw simple lines between species and make nice family trees. And we have to understand that is our need. That's our desire, that's not necessarily the way that nature works.

NARRATOR: It's very natural to think about human evolution as a sort of family tree in deep time, but evolution is much more complex than that.

CAROL WARD: Evolution is bushy. There are different experiments. Populations try different adaptations. They try different ways of being about the world.

NARRATOR: Paleoanthropologists talk about the bushiness of human evolution as a metaphor for the many types of early hominins and the difficulty of knowing which one led to us, but even that metaphor may not do justice to the way evolution works.

STEVE CHURCHILL: Nature is messy. Nature is complicated. Nature does not really respect our desire to put fossils into neat bins and to, sort of, name nice neat species.

NARRATOR: Both sediba and naledi have a mosaic of Australopith and Homo features. They seem to show that, at the dawn of humanity, there were multiple evolutionary experiments with small-bodied, small-brained upright walking apes.

Scientists now know some of these varieties of late Australopith and early Homo lived together at the same time. And some of them may have been interbreeding.

STEVE CHURCHILL: These aren't fully formed species, and there's a lot of interbreeding between these groups. Some adaptive features are evolving in one group, other adaptive features are evolving in other groups, and by interbreeding those are coming together. And if that's the case we may never be able to draw neat lines between any of these groups and later Homo.

NARRATOR: Perhaps now we need a new metaphor to help us understand our evolution, one that expresses better the dynamic and fluid nature of it.

LEE BERGER: Now, perhaps the best metaphor is a braided stream. And that's brought on by discovery of these mosaic hominines like naledi, sediba and others. They're showing us there's lots of experiments going on.

NARRATOR: Some of these evolutionary experiments died out, others came together and interbred. The ebb and flow of genes through these groups was probably so complex that we may have to give up hope of discovering a simple linear evolution.

LEE BERGER: So imagine, in your mind, a glacier in the top of a valley and what happens is as it melts: it creates many, many rivulets, and some of them are large and some are small, and they all move off down the valley. And almost inevitably, at the end of that valley is going to be a lake, of which some, maybe the majority, but not all are contributing to. I think we have to begin looking at these species we're finding as almost individual channels in a braided stream. It's clear they have something to do with the end population—and that's us, the billions of human beings alive today—but it's hard to tell which one's the most responsible for us being here.

NARRATOR: The new finds, on the plains of South Africa, are adding a vital new chapter to the story of our origins. The tantalizing gap in the fossil record at the beginning of our genus is being slowly filled in. Finally, there is light at the dawn of humanity.