Older than Lucy, "Ardi" reveals startling new details about the evolution of the hominid family tree.
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00:00:00Every human being has one common question. Where did we come from?
00:00:14Where do we come from? It's a profound human question.
00:00:23In the beginning, we humans have seemed so different from the rest of the animal world.
00:00:33Then came Darwin. He concluded that human beings, like all living creatures, evolved
00:00:41through natural selection, but he didn't have the human fossils to support his ideas.
00:00:48Now, from a remote African desert, buried for more than four million years, comes the
00:00:54fossil evidence Darwin could only have dreamed of.
00:01:01An international team of scientists has made a major discovery in Ethiopia.
00:01:26We have recovered a partial skeleton dating to 4.4 million years ago. We have something
00:01:33that takes us back 4.4 million, closer to a common ancestor that we shared with the
00:01:39African apes.
00:01:50Tim White is part of the Middle Awash research team.
00:01:52We're here in the Middle Awash study area of Ethiopia, and we're looking at a series
00:01:58of basaltic ashes, volcanic explosions, that covered this landscape 4.4 million years ago.
00:02:06In the sediments underneath those volcanic horizons, we have fossil bones, fossil bones
00:02:14of our own ancestors.
00:02:18This is an absolutely unique geological extension in this area, letting us look deeply into
00:02:24the past, into our own family history, as well as into the evolutionary history of all
00:02:29the rest of the African mammals.
00:02:37The Middle Awash research project is looking for ancient human ancestors in Ethiopia's
00:02:42rugged badlands. Ethiopia lies in the Horn of Africa. It's a place of towering highlands,
00:02:59scorching deserts, and vast lakes.
00:03:08This land is a crossroads of early cultures and religions. But there are far deeper roots
00:03:15of human existence here, roots that bind all living people together.
00:03:22Hadar, in northeastern Ethiopia, was the site of an historic fossil discovery in 1974.
00:03:35Researchers, led by Maurice Tayeb and Don Johanson, found the partial skeleton of a
00:03:40female human ancestor, 3.2 million years old. The find captured public imagination around
00:03:48the world.
00:03:53Scientists named the new species Australopithecus afarensis, and nicknamed the skeleton Lucy.
00:04:05Most experts had predicted that the anatomy of a fossil as old as Lucy would fall about
00:04:09halfway between modern humans and the common ancestor we once shared with living chimpanzees.
00:04:18But that prediction collapsed when the Lucy skeleton was analyzed at the Cleveland Museum
00:04:22of Natural History.
00:04:26Tim White worked with Johanson to interpret the fossils, along with Owen Lovejoy, a leading
00:04:31human anatomist.
00:04:35When Lovejoy examined Lucy's pelvis, he realized she did not mark some halfway point between
00:04:41humans and chimpanzees. In fact, her anatomy showed that she walked upright, on two legs.
00:04:49That meant Lucy belonged to her own zoological family. She was on our branch of the family
00:04:54tree, a hominid.
00:05:03What I had thought was a transitional fossil was in fact something that had been bipedal
00:05:08for a very long period of time, and as a consequence, didn't really answer the question that we
00:05:13needed to answer, which is when and why did bipedality actually first evolve?
00:05:21But at 3.2 million years old, Lucy was already too human to answer a fundamental question.
00:05:29Why do we humans walk so differently from all other mammals?
00:05:36To find the answer, scientists realized they'd have to find even earlier fossils.
00:05:44In 1981, legendary archaeologist Desmond Clark assembled a new research team.
00:05:56Clark knew that the only way to find an older ancestor of Lucy was to explore much older
00:06:01sediments that lay south of Hadar.
00:06:07So a multinational team formed, with funding from the National Science Foundation of the
00:06:11United States. They began to prospect the Middle Awash Valley, named for the river flowing
00:06:18through the region.
00:06:20Here, some sediments were millions of years older than at Hadar.
00:06:30For three field seasons, Middle Awash scientists searched east of the river, working in the
00:06:36sweltering heat.
00:06:38The heat sometimes can get up to 44 degrees centigrade in the middle of the day, no shade,
00:06:46and it's easy to die of heat stroke.
00:06:51For months, the team scoured the barren outcrops. They found hundreds of animal fossils, but
00:06:58no signs of ancient hominids.
00:07:04Around the same time, tensions between local tribes began to heat up. The area was no longer
00:07:11safe, so the team was forced to move their search to the other side of the Awash River.
00:07:18In 1992, we started fieldwork on this side, on the west side of the Middle Awash. That
00:07:23is a year, basically, we changed everything.
00:07:30On December 17th, the desert gave up an ancient secret near the small Afar village of Aramis.
00:07:40We were out walking those eroding deposits, reddish-brown in color, and Gensua found in
00:07:48amongst a lot of monkey fossils and fossil wood, he found a molar tooth. And it was the
00:07:55molar tooth of a hominid.
00:08:01This single fossil tooth marked the beginning of a series of discoveries that would forever
00:08:06change the way we think about our place in nature.
00:08:12Two days later, Ethiopian collector Alamayu Asfal discovered a child's jaw with its baby
00:08:19molar still attached, another major find.
00:08:24Gann and I looked at that molar and said, wow, we are looking at something very new
00:08:28here. We knew we had something really exciting and important. So we decided to do another
00:08:35field season to see what else we could find in those sediments at Aramis.
00:08:41The next season, the Middle Awash team began what's called a 100% collection. Like a forensics
00:08:48unit at a crime scene, they combed every square inch of the blistering desert search
00:08:53area. A local Afar tribesman, Gadi Hamed, found something extraordinary, a set of teeth
00:09:02all from the same individual. But there was more.
00:09:09While we were doing the recovery operation, Alamayu, one of the great fossil collectors
00:09:13of all time, walked over the hill and came back and he had discovered an arm bone.
00:09:21The Middle Awash team had discovered a new and ancient hominid, one that predated Lucy
00:09:27by more than a million years. In the September 1994 issue of the journal Nature, they announced
00:09:35their discovery to the world and named this new creature Ardipithecus ramidus.
00:09:44When we first announced it in Nature in 1994, a lot of people said, well, you know, do you
00:09:50think you're going to find something as complete as Lucy? And I said, no, I really don't think
00:09:55so.
00:09:58The team had fossil teeth and bone fragments from 17 individuals, but no skeleton. Enough
00:10:06evidence to announce a major discovery, but not enough to shed much light on the creature
00:10:11itself.
00:10:17We only had a collection of bones that I could literally hold all of those bones in two hands.
00:10:25That was all we knew of this Ardipithecus ramidus creature. We wanted more.
00:10:33The project scientists returned to Aramis in 1994 to continue the search.
00:10:48But finding ancient fossils out here was not an easy job. Ancient Aramis was crawling with
00:10:56scavengers who chewed most fallen animals to pieces.
00:11:01The problem we have is at a place like Aramis, most of the bodies were immediately ravaged
00:11:09by hyenas. And hominids in those days were no different. As soon as they hit the ground,
00:11:16the hyenas would have been there chewing them to bits. The chances of us finding a skeleton
00:11:23under these depositional conditions, the chances of that, very, very low.
00:11:28Yohannes Haile-Selassie was a graduate student at UC Berkeley.
00:11:33We were like ten or twelve people here. We were sort of crawling, semi-crawling this
00:11:41area, just shoulder to shoulder in a line. And this was probably about 4.30 in the afternoon
00:11:47when I picked up a little fragment of a hand bone, which was in this gully right here.
00:11:59So we had to come back the next day and when we came back we started finding more finger
00:12:04bones, more than two, three pieces. And obviously at that point we knew that we had more than
00:12:09just a hand.
00:12:14As the sediment is carefully swept from the surface, the scientists uncover an embedded
00:12:21leg bone.
00:12:24It was so fragile you couldn't even breathe on the thing. You had to drop preservative
00:12:30onto this specimen to solidify it, to effectively turn it into stone. And it was in this cracking
00:12:36sedimentary matrix, expanding and contracting with each rainstorm, so this was just about lost.
00:12:44We started to think, well, maybe this tibia belongs to the same individual whose hand
00:12:50bones we'd been finding.
00:12:54November 9th, heavy, unseasonable rains hit the middle Awash Valley. Flooding and deep
00:12:59mud confined the team to camp. All work is stopped.
00:13:08More and more rain came. The river next to our camp was in flood and it was in fact overbanked.
00:13:14We were pulling the kitchen up away from the channel trying to save the food.
00:13:22It took days for the rains to finally end.
00:13:29After the ground dried out a little bit and was actually excavatable, we started to dig
00:13:36into this little tiny hill, hoping that the rest of a skeleton was inside.
00:13:44The prediction here is that as we excavate through this horizon, down through this little
00:13:50hill, we will find more specimens. And all we can do now is excavate and hope for the best.
00:14:00As the team continued to carefully probe the sediments, more and more fossil bones were recovered.
00:14:06At the time, the scientists had no idea that this would be just the beginning of a 15-year
00:14:13cold case investigation of a body buried in the Ethiopian desert for millions of years.
00:14:36Deep in the Ethiopian desert, the Middle Awash team continued their recovery operation,
00:14:41and more and more fossils emerged from the little hill at Aramis.
00:14:48Piece after piece, we lifted out. We got the pelvis. It was broken to pieces, but we got
00:14:54a lot of it. We got the base of the cranium. We found the lower jaw. We found the inner
00:15:01ankle bone. We found foot bones. We found other leg bones. We found arm bones.
00:15:10We had a partial skeleton.
00:15:15By the end of the 1994 field season, the team had found an amazing 90 fossil bones, teeth
00:15:22and bone fragments in the little hill at Aramis.
00:15:27They all belonged to a single Ardipithecus individual. The scientist nicknamed it Ardi,
00:15:33a creature who lived and died more than a million years before Lucy.
00:15:41Could these fossil remains, now safely wrapped in plaster jackets, answer the questions that
00:15:47Lucy could not?
00:15:49Could Ardipithecus help solve the riddle of where we humans come from and why we seem
00:15:54so different from other mammals?
00:16:03Imagine looking for a missing person in the vastness of Africa. A person dead for more
00:16:09than 4 million years and covered by tons of sediments, hundreds of years old.
00:16:15Imagine all that and you begin to understand how hard it was to find a skeleton as old
00:16:21as Ardi's.
00:16:26But the Middle Awash research team did just that when they discovered the fossil remains
00:16:31of Ardipithecus ramidus, deep in the Ethiopian desert.
00:16:35Hominids are incredibly rare. They were rare on the landscape. They have very long lifespans
00:16:42so few of them die and end up with carcasses on the landscape. They're very smart, smarter
00:16:47than most mammals, so you don't find very many of them trapped in this area.
00:16:51They're also very hard to find.
00:16:53They're also very hard to find.
00:16:55They're also very hard to find.
00:16:57They're also very hard to find.
00:16:59They're also very hard to find.
00:17:02They're extremely rare.
00:17:06It was sort of a surprise to us to find so many pieces of a single individual in this
00:17:12small area because in the fossil record that usually doesn't happen.
00:17:22These delicate fossil bones of Ardipithecus now become precious hard evidence.
00:17:29But evidence of what?
00:17:34After a long and exhausting field season, the team had excavated dozens of pieces of
00:17:39this new skeleton.
00:17:47But one crucial part of Ardi still eluded them.
00:17:51We wanted a face. We wanted to have the whole cranium together to see what was going on
00:17:57to see what this creature looked like.
00:18:01Within days of returning to the excavation site for the next field season, they got their
00:18:06wish.
00:18:09The upper jaw, the side of the eye socket, the frontal bone above the eye socket, and
00:18:16the other side of the skull were all uncovered.
00:18:21They were all in different pieces, all scattered around, all very crushed, all extremely fragile.
00:18:27If you liken it to a forensic case, it was a case where you would have to do a lot of
00:18:32work to put this all back together to get to the individual's face, and indeed that's
00:18:36what we proceeded to do.
00:18:43Even as the search for more remains continued, one key question had yet to be fully answered
00:18:49by the project's geologists.
00:18:51Exactly how old were these fossils?
00:18:57This Ardi skeleton was so ancient, its fossilized bones no longer contained any material useful
00:19:03for dating.
00:19:05We don't really date the bones themselves, so we rely on geologists to give us dates
00:19:10for these rocks that are above and below the fossils that we're finding.
00:19:18But not just any rocks would do.
00:19:20For millions of years, the fractured crust beneath Africa's Great Rift Valley has produced
00:19:25volcanoes.
00:19:32Ash layers and lava flows from more recent eruptions cover the rift floor today, just
00:19:37as they covered the ancient landscapes long ago.
00:19:41The geologist can identify and trace each layer of ash through its own unique, unique
00:19:48geochemical fingerprint.
00:19:50At Aramis, they got lucky.
00:19:52Instead of the fossils just lying near a single volcanic layer, they were actually sandwiched
00:19:58between two layers of ash.
00:20:02It was a nice coincidence to have those two volcanic rocks bracketing that sedimentary
00:20:07sequence, and so I collected several samples from that area for dating.
00:20:14Dr. Gidei Woldegabriel analyzes the Aramis samples at Los Alamos National Laboratory.
00:20:21First, he pulverizes and refines them.
00:20:31Next, he separates and extracts tiny crystals and shards of volcanic glass.
00:20:37This material contains trace amounts of volcanic ash.
00:20:41This material contains trace amounts of argon gas produced by radioactive decay.
00:20:47The gas has gradually built up inside the rock ever since the eruption.
00:20:56Woldegabriel now sends the processed samples to Dr. Paul Rennie at the Berkeley Geochronology Center.
00:21:02Hey, Leah.
00:21:03Hey, Paul.
00:21:04Hey, these samples are ready.
00:21:05Oh, for the middle Alamos?
00:21:06Yeah, I just looked at them and they look great.
00:21:11Rennie uses a laser to melt the ancient volcanic glass and crystal fragments.
00:21:16This releases the built-up argon gas.
00:21:19By measuring the amount of gas, Rennie can determine the sample's age.
00:21:25The more argon gas, the older the rock sample is.
00:21:30His results date the Aramis fossils more precisely than anyone expected.
00:21:36We cannot tell the difference in age between the unit that's above the Aramis fossils
00:21:41and the unit that's below.
00:21:43So, in each case, we get an age of 4.4 million years
00:21:48and those two results are analytically indistinguishable.
00:21:54We estimate that we know the age of Aramis to within about 50,000 years.
00:22:01So, that's 4.4 million plus or minus about 50,000 years.
00:22:07That's very good.
00:22:09That's about as good as it gets.
00:22:13At 4.4 million years old, the fossil hominid skeleton found at Aramis
00:22:18is the earliest ever discovered.
00:22:22These fossilized bones belong to a creature
00:22:26that lived and died 100,000 generations before Lucy was even born.
00:22:34All that time has taken a heavy toll on the fossil skeleton.
00:22:39Even some of the teeth have been crushed and distorted.
00:22:43The laboratory extraction and analysis of the fossils will be slow and meticulous.
00:22:50It will take more than a decade of painstaking research
00:22:54by a huge team of scientists to see what this creature looked like
00:22:58and to understand how it might have moved through its now vanished world.
00:23:11Most of us know our parents, our grandparents,
00:23:14our grandparents, our grandparents,
00:23:17but go back five or ten generations,
00:23:20and many of us lose our individual genealogies.
00:23:24Few of us are able to trace our family into the Middle Ages.
00:23:32Some 300 generations separate living Egyptians
00:23:35from their ancestors who built the Great Pyramids.
00:23:39Now, on a small patch of Ethiopian desert,
00:23:42an international team of scientists has found the remains of a creature
00:23:461,000 times older than the pyramids.
00:23:53The crushed and broken skull and pelvis of this partial skeleton
00:23:57could help reveal how all of our ancestors lived and died.
00:24:02The crushed and broken skull and pelvis of this partial skeleton
00:24:06could help reveal how all 7 billion of us have come to be human.
00:24:17At the end of each field season,
00:24:19the researchers take their fossil finds back to Ethiopia's National Museum
00:24:23in Addis Ababa for safekeeping, cleaning and analysis.
00:24:32The hominid fossil collection here is one of the most impressive in the world.
00:24:39Now, each of the fragile new fossils
00:24:42will have to be freed from the sediments that surround them.
00:24:45The scientists take extreme care
00:24:48not to damage the fossils during the cleaning process.
00:24:51Hours, sometimes weeks, are spent working on a single piece.
00:24:56We couldn't even lift the bones without putting plaster jackets around.
00:25:02This is one of the ribs.
00:25:04We used a lot of hardener in the field
00:25:07to cement this rib and the matrix in place
00:25:10so it wouldn't move in transport to the lab.
00:25:13Now, to study the rib and to piece the various pieces back together again,
00:25:16we have to remove this matrix.
00:25:21The time invested in this stage of the project is remarkable.
00:25:25The painstaking work to safely free the fossil bones
00:25:29from the surrounding matrix takes over three and a half years.
00:25:37With the fossil bones exposed and stabilized,
00:25:40the researchers can now conduct a post-mortem investigation.
00:25:43They want to discover as much as they can
00:25:46about what this creature was like when it was alive.
00:25:51So it's sort of like a paleo-autopsy.
00:25:54And to run that autopsy, one of the first things you want to establish
00:25:58is, is this a male or a female?
00:26:01For that, we can go to the canine teeth.
00:26:04We have this complete lower dentition.
00:26:08The smallest canine of any Ardipithecus found
00:26:11is in this individual.
00:26:14Very strong indication that she was a female.
00:26:18We know that she was an adult when she died
00:26:21because her molars had been fully erupted
00:26:24and were hardly in wear.
00:26:28She was a female.
00:26:32It began as the coldest of cold cases.
00:26:35But now, facts from Artie's life
00:26:38slowly begin to emerge.
00:26:43We know details of her biologies.
00:26:46For example, in one of her foot phalanges,
00:26:49this is a toe bone,
00:26:52we have an infection that persisted in this individual
00:26:55during her ability to move around the landscape
00:26:58at some times, probably, but the bone healed over.
00:27:01It resorbed and healed over.
00:27:04This is a pathology that this individual probably survived.
00:27:08But what about the survival of the fossils themselves?
00:27:11To study Artie thoroughly,
00:27:14researchers will have to handle them over and over again.
00:27:20To protect the precious originals,
00:27:24they will have to make new replicas
00:27:27accurate to within a tenth of a millimeter.
00:27:33Artie's fossil bones have made
00:27:36an incredible journey through time,
00:27:39one that's not over yet.
00:27:46In 2003, the Ethiopian government
00:27:49allows the original skeleton to travel to Japan
00:27:53for a new phase of analysis.
00:27:56The fossils are under the protection
00:27:59of Dr. Yonas Beyene.
00:28:02Along with project scientist Gen Suwa,
00:28:05Beyene arrives at Tokyo airport
00:28:08with a priceless cargo in a sturdy blue suitcase.
00:28:11These fossils are the result of ten years
00:28:14of intensive field research
00:28:17by researchers from all over the world.
00:28:20It gives you a sensation that it's something
00:28:23which goes deep into your spine.
00:28:26If something happens,
00:28:29you are not losing only those precious materials,
00:28:32but precious also to science.
00:28:38Artie and her two companions
00:28:41head for the University of Tokyo.
00:28:44Here, Suwa will probe her skeleton
00:28:47using one of the most powerful CT scan machines.
00:28:50This equipment will let them make high-resolution slices
00:28:53through Artie's bones and teeth
00:28:56without damaging the fossils.
00:29:01They'll be able to digitally reassemble Artie's crushed skull
00:29:04and even measure the size of her brain.
00:29:09They're also looking for clues
00:29:12to the greatest question of all.
00:29:16Prop it up on the machine like that.
00:29:21Ever since Darwin,
00:29:24the idea that we humans evolved from an ancient ancestor
00:29:27who looked and acted much like a modern chimpanzee
00:29:30has been widely accepted.
00:29:34It seems to make sense that millions of years ago
00:29:37there was some kind of transitional,
00:29:40chimp-like species that walked on two legs
00:29:43instead of on all fours.
00:29:47Were the Artie fossils from that creature?
00:29:54Clues from Artie's pelvis might help answer this question.
00:30:00Early in the investigation,
00:30:03Lovejoy identified a distinctive clue
00:30:06on the intact front edge of Artie's pelvis,
00:30:09a small feature with big implications.
00:30:12It was a shape common to all hominids
00:30:15and was clear evidence that Artipithecus
00:30:18didn't move on all fours
00:30:21but walked upright on two legs.
00:30:25She was bipedal, like us.
00:30:31Following up on this early sign that Artie was bipedal,
00:30:34the team cleaned and studied more of the badly broken pelvis.
00:30:43Separating the original fossil fragments
00:30:46and putting them back together by hand was out of the question.
00:30:49There were simply too many
00:30:52and they were all too fragile to handle.
00:31:01Now Lovejoy realizes he will need to make
00:31:04an accurate restoration of Artie's pelvis.
00:31:07To do this, he'll use his knowledge of primate anatomy
00:31:10along with a cutting-edge technology called micro-CT scanning.
00:31:13SUA's laboratory in Tokyo
00:31:16is one of the few in the world equipped for this task.
00:31:22In December of 2003,
00:31:25SUA and Biene arrive at the University of Tokyo Museum
00:31:28with Artie's fragile bones intact.
00:31:41Using the museum's CT scanner,
00:31:44SUA will take eight weeks
00:31:47to produce thousands of high-res scans of Artie,
00:31:50the most comprehensive mapping
00:31:53of an ancient hominid skeleton ever attempted.
00:31:59The team wants to learn as much as possible about Artie's skeleton.
00:32:02The scanner will allow them to study
00:32:05both the inside and the outside
00:32:08of each fossil bone and tooth.
00:32:13Here's one of Artie's 4.4 million-year-old molars
00:32:16seen from the surface
00:32:19and scanning down into the fossil tooth.
00:32:24SUA will work 16-hour days
00:32:27to make thousands of these precision scans,
00:32:30pushing both himself and the technology to the limit.
00:32:39And now, 15 years after Artie's pelvis
00:32:42was unearthed in Ethiopia,
00:32:45the scientists' long investigation
00:32:48is finally helping to answer the question
00:32:51of how this strange new hominid moved.
00:32:59If I compare the pelvis of a chimpanzee
00:33:02to Ardipithecus' pelvis,
00:33:05what you see is a dramatic set of differences
00:33:08in all of the anatomical characters.
00:33:14This is the pelvis of an animal that locomoted bipedally.
00:33:17It just wasn't as highly evolved in doing so as was Lucy.
00:33:26The pelvis reconstruction has confirmed
00:33:29that Ardipithecus was bipedal,
00:33:32a major step forward in the investigation.
00:33:41Another key part of Artie's anatomy is her skull.
00:33:44An accurate reconstruction of the skull
00:33:47could provide the scientists with a number of insights,
00:33:50including the size of Artie's brain.
00:33:53Once again, the original fossils in Africa
00:33:56are the starting point,
00:34:00and once again, the collaboration would span the globe.
00:34:08At Aramis, the team had recovered
00:34:1134 separate pieces of Artie's skull,
00:34:14including her jaws and teeth,
00:34:17but many parts were never found.
00:34:21In Tokyo,
00:34:24Suwa will reconstruct the Artie's skull
00:34:27using CT scans,
00:34:30filling in missing parts digitally.
00:34:33In Berkeley, California,
00:34:36White will also rebuild the Artie's skull,
00:34:39but to make his version,
00:34:42he'll use plaster casts of the fossils.
00:34:45Working this way,
00:34:48they're able to cross-check their results independently.
00:34:53Suwa scans the cranial fragments,
00:34:56then he uses the CT slices
00:34:59to properly restore each bone.
00:35:12Front teeth are added,
00:35:15and a new part, Epiphagus, begins to emerge.
00:35:23The digital reconstruction process would take years.
00:35:28Finally, a composite CD assembly
00:35:31is output from a computer
00:35:34as a 3-D plastic version called a stereolith.
00:35:37Suwa sends it to Tim White in Berkeley.
00:35:40So this restoration was accomplished
00:35:43in Tokyo.
00:35:46This restoration was accomplished physically
00:35:49here in Berkeley.
00:35:52When we compare these two independent reconstructions,
00:35:55we're seeing effectively the same face.
00:36:02The scientists have now reassembled
00:36:05the face of this enigmatic creature,
00:36:08seen for the first time in 4.4 million years.
00:36:11She had a very small brain,
00:36:14and yet her pelvis shows she walked bipedally.
00:36:17Artie seems to have a foot in two worlds.
00:36:21What other secrets
00:36:24did the rest of her strange skeleton hold?
00:36:37Whether it's crossing a street
00:36:40or walking down on the surface of the moon,
00:36:43we humans do it on two feet.
00:36:47In 1969,
00:36:50Neil Armstrong's footprints on the lunar surface
00:36:53became symbols of our scientific progress.
00:36:56Nine years later,
00:36:59the discovery of a series of fossilized footprints
00:37:02in Tanzania revealed that our ancient ancestors
00:37:05had made a giant leap of their own.
00:37:08What came to be known as the Laetoli footprints
00:37:11were made by members of Lucy's species.
00:37:14They established that hominids were already walking upright
00:37:17on human-like feet some 3.7 million years ago.
00:37:26But what about Artie's feet?
00:37:29They're nearly a million years older than the Laetoli footprints.
00:37:32What could they tell us
00:37:35about the beginnings of bipedality?
00:37:39While cleaning the Ardipithecus skeleton,
00:37:42the scientists were stunned to see the shape of a bone
00:37:45near the center of Artie's foot.
00:37:49The real shocker
00:37:52was the medial cuneiform from the foot
00:37:55because it told us that we had a grasping foot
00:37:58just like you'd see in a chimpanzee.
00:38:06This bizarre combination
00:38:09of a primitive grasping big toe
00:38:12in the foot of a biped was unprecedented.
00:38:17The skeleton's curious mixture
00:38:20of primitive and derived traits
00:38:23revealed that Artie was neither chimp nor human.
00:38:26She was an evolutionary mosaic.
00:38:30Artie's chimp-like big toe
00:38:33was just one of the many surprises
00:38:36found during the investigation of her skeleton.
00:38:39Another would come from the bones
00:38:42that made up her hand.
00:38:45Artie's hands were remarkably complete.
00:38:48Even tiny sesamoid bones
00:38:51that once rested within the tendons of her fingers
00:38:54were recovered.
00:38:58Did the earliest hominids like Ardipithecus
00:39:01evolve from ancestors who walked on their knuckles
00:39:04the way living chimpanzees do?
00:39:07Using Artie's reassembled hand,
00:39:10the project scientists would now be able to test this hypothesis.
00:39:15One of the important things about human evolution
00:39:19that Ardipithecus informs us about
00:39:22is not only the foot and the pelvis and the back
00:39:25and these other parts, but in particular the hand.
00:39:28And the hands of chimpanzees and humans are quite distinct.
00:39:36Chimps feed on ripe fruit.
00:39:39To get to it, they often climb large trees.
00:39:42Up in the branches, they often suspend themselves
00:39:45using their long forelimbs and stiffened wrist joints.
00:39:51Down on the ground, those same stiffened wrists
00:39:54act like shock absorbers at the base of their long hands.
00:39:57There, they practice a peculiar form of locomotion
00:40:01called knuckle-walking.
00:40:06Most scientists predicted that the deeper the fossil record went,
00:40:10the more chimpanzee-like our ancestors would be.
00:40:15If humans had descended from a chimp-like ancestor,
00:40:18there ought to be traces of this knuckle-walking anatomy
00:40:21in the structure of Ardi's fossilized hand bones.
00:40:24But there aren't any.
00:40:28It was quite obvious the minute we found the major elements
00:40:32of the Ardipithecus hand
00:40:35that it was not a knuckle-walker.
00:40:38The metacarpals, the long bones that you see here, are quite short.
00:40:42And if we rotate that a little bit
00:40:46and we look at the surface of the top of the metacarpal,
00:40:51the elements that we would expect to find
00:40:54in a knuckle-walker are not present.
00:40:57So these bones are short,
00:41:00and the whole head morphology is completely different.
00:41:03And it wasn't until we'd extracted the hand bones
00:41:06and studied the hand bones that we came to realize
00:41:09that this was not the hand of an ape.
00:41:14This is compelling evidence
00:41:17that our common ancestor with chimpanzees
00:41:20did not walk on its knuckles.
00:41:24This was a completely new animal.
00:41:27It took years as a consequence
00:41:30to look at all the details of things like the wrist bone
00:41:34to figure it all out,
00:41:37because we've never seen anything like this before.
00:41:41Ardipithecus did not evolve from an ancient chimpanzee.
00:41:45This conclusion, based on new fossil evidence,
00:41:49has overturned a concept so widespread
00:41:52that many people just assumed that it was true.
00:41:56From the beginning, we've used chimpanzees and gorillas
00:42:00as our stand-ins, if you will, for the last common ancestor.
00:42:05We can't do that anymore.
00:42:10Ever since Darwin, we've bought into the idea
00:42:13that humans evolved from ancient, chimp-like creatures.
00:42:17That's because modern chimps seem to share
00:42:20a lot of anatomy and behavior with we humans.
00:42:23So the idea that we evolved from something like chimps
00:42:27seems to make sense.
00:42:29But now the discovery of Ardipithecus
00:42:32shows that this idea is totally and completely wrong.
00:42:38It's an early transitional bipedal form with small canines,
00:42:43a completely unique and unexpected primate
00:42:46that no one could have known
00:42:49until we found the skeleton at Eremus.
00:42:55Ardi's skeleton sheds new light on how humans evolved,
00:43:00but what influenced and shaped that evolution?
00:43:08The Middle Awash investigators
00:43:12were not finished making discoveries.
00:43:16The team would go on to also test
00:43:20another fundamental assumption about our origins.
00:43:24Scientists had long predicted that early hominids
00:43:28evolved bipedality on Africa's open savannas.
00:43:32But without fossil evidence,
00:43:35this hypothesis has been impossible to test.
00:43:39Was Ardi's world really a savanna,
00:43:43or was it something else?
00:43:46Now, the most extensive investigation
00:43:49of plant and animal fossils in the history of paleoanthropology
00:43:53would answer this question in a very unexpected way.
00:43:59The search for fossils at Eremus
00:44:02is physically demanding and often dangerous work.
00:44:07Patience and determination make all the difference.
00:44:11Time is not really a limit for us.
00:44:14The only thing that we have to limit
00:44:17is the amount, the time that we have to waste
00:44:21to find the fossils.
00:44:24And time does add up.
00:44:27The Middle Awash researchers have spent over a decade
00:44:31examining and reconstructing Ardi's partial skeleton.
00:44:35During the same period,
00:44:38a parallel effort has been underway,
00:44:41an exhaustive global study that would challenge assumptions
00:44:45about how and where early hominids arose.
00:44:49The team set out to investigate
00:44:52the community of plants and animals
00:44:55that lived in Ardi's ancient world at Eremus.
00:44:59We can't see Ardipithecus today.
00:45:02We can only see it through its skeletal remains.
00:45:06But we can see its world.
00:45:09We can reconstruct its world.
00:45:12We can understand its world
00:45:15through using this very, very rich paleontological record.
00:45:24For nearly a century, it's been assumed
00:45:27that the earliest hominids lived and evolved in a savanna grassland.
00:45:31The Eremus site gave the Middle Awash scientists
00:45:35a unique chance to test that hypothesis with hard evidence.
00:45:40The scientists continued to return
00:45:43to the harsh Ethiopian desert year after year,
00:45:46even after the Ardi skeleton was found.
00:45:49Their objective was to recover as many fossils as they could
00:45:53of the plants and animals who lived with Ardi.
00:46:02But the fossils at Eremus are mixed with rocks and other debris
00:46:06that are virtually the same color.
00:46:09And so are the snakes.
00:46:14We've had dozens of instances
00:46:17in which our fossil collectors have come literally eyeball to eyeball
00:46:21with these highly venomous snakes.
00:46:25This is just one of the dangers,
00:46:29one of many dangers of working in a remote area like this.
00:46:34Through this systematic search at Eremus,
00:46:37thousands of fossils have been recovered.
00:46:40And each year, the seasonal rains expose even more fossils,
00:46:44including other primates.
00:46:47Look at this. That's an immature monkey
00:46:51whose jaw dropped to the ground here 4.4 million years ago.
00:46:55And it's a baby monkey.
00:46:58The dentition will go right together
00:47:01just like that.
00:47:04One of the reasons people are interested in monkeys
00:47:07is that they are the other primate that you find at the hominid sites.
00:47:11So they can tell you a bit about the paleoenvironment,
00:47:14what was going on at the time.
00:47:17The monkeys can tell us quite a bit.
00:47:20Were they arboreal monkeys?
00:47:23Were they terrestrial?
00:47:26Many remains of arboreal monkeys were found at Eremus.
00:47:30Helping to make the case
00:47:33that this was an environment filled with trees.
00:47:38The scientists also combed the sediments
00:47:41for fragments of mouse-sized creatures called micromammals.
00:47:49Back at camp, excavated chunks of sediment
00:47:52are dissolved into thick mud
00:47:55and then run through sieves with submillimeter-sized mesh.
00:47:59As water runs through the mix,
00:48:02fragments of bones and teeth are separated.
00:48:05Later on, they'll be sorted and identified in the lab.
00:48:13Reconstructing Arte's ecology
00:48:16will eventually involve over 40 scientists
00:48:19from 16 countries,
00:48:22representing 30 different institutions from around the world.
00:48:26They've even studied the ancient soils she walked on
00:48:29and profiled the chemical composition of her teeth
00:48:32to learn about her habitat and diet.
00:48:35For more than 10 years,
00:48:38the field team has collected fossils from the same sediments
00:48:41that also buried Arte at Eremus.
00:48:45At Ethiopia's National Museum,
00:48:48experts sorted, analyzed, and catalogued
00:48:51thousands of remnants from the now-vanished world
00:48:54of Artepithecus.
00:48:57A porcupine, a mongoose,
00:49:00a bunch of birds,
00:49:03all kinds of monkeys,
00:49:06pigs,
00:49:09bovids...
00:49:12Even finger bones of micromammals like shrews and bats are recovered.
00:49:15These tiny bits of evidence
00:49:18will join thousands of other clues.
00:49:22This is the lower jaw of a fruit bat
00:49:25who flew in the skies over Eremus
00:49:284.4 million years ago and would have looked down
00:49:31to see Artepithecus.
00:49:34The fruit bat would have seen something else
00:49:37as it flew over Arte's world.
00:49:40Trees. Lots of trees.
00:49:43These fossilized seeds fell from trees that once grew
00:49:46not on an African savanna, but in a dense woodland.
00:49:52This came out in the last rain.
00:49:55What we have here are fragments of fossilized wood.
00:49:58We have not seen fossilized wood
00:50:01coming out from these salmon cover sediments
00:50:04beyond the mammalian fossils.
00:50:07So since the last rain this week,
00:50:10we're starting seeing a lot of plants
00:50:13that were associated with these organisms
00:50:164.4 million years ago.
00:50:22For nearly a century, it's been widely believed
00:50:25that humans evolved bipedality in Africa's open savannas.
00:50:31Now, this long-held savanna idea
00:50:34has been overturned by a decade of field work
00:50:37and an avalanche of solid fossil evidence.
00:50:42So all theories are being knocked out
00:50:45by new discoveries from the Mid-Laos.
00:50:48In terms of what we're doing here and what we're finding.
00:50:54The investigators have now established
00:50:57ancient Arte's habitat.
00:51:00But what about Arte herself?
00:51:03If all her parts, skin, muscles, bones, and teeth
00:51:06were restored and reassembled,
00:51:09what would this strange African creature have looked like?
00:51:12To bring Arte back to life,
00:51:15it now turns to one of the world's greatest
00:51:18natural history artists, J. Maternus.
00:51:21It's a privilege.
00:51:24And a challenge.
00:51:33The science team has now spent over a decade
00:51:36examining the Artepithecus skeleton piece by piece.
00:51:39Now it's time to put all the pieces together
00:51:42by harnessing science to art.
00:51:47This process goes back to the time of Leonardo da Vinci,
00:51:50who created lifelike human images
00:51:53based on his own detailed anatomical drawings.
00:51:59Now, using the same technique,
00:52:02one of today's most accomplished natural history artists
00:52:05takes on a creature da Vinci could have never imagined.
00:52:13For illustrator J. Maternus,
00:52:16the challenge of creating the first
00:52:19lifelike scientific drawings of Arte has become a passion.
00:52:24Right now, of course, Arte has consumed
00:52:27all of my attention
00:52:30because it's so demanding.
00:52:33And as I say, it's such an outstanding fossil,
00:52:36the significance of which is profound.
00:52:42Project scientists have asked J.
00:52:45to create the official scientific portraits of Arte.
00:52:50His drawings will be released to the public
00:52:53and scrutinized by countless scientists
00:52:56around the world as well,
00:52:59so accuracy is the absolute priority.
00:53:02Over the years, Maternus has collaborated
00:53:05with leading scientists to create lifelike,
00:53:08scientifically based drawings of human ancestors,
00:53:11including Lucy's species at Laetoli
00:53:16and at Hadar.
00:53:22Maternus often functions like a sketch artist
00:53:25in a criminal investigation,
00:53:28but the drawings of Arte Pithecus
00:53:31will demand a much higher level of detail.
00:53:36Ten years into the project,
00:53:39J. will make a visit to Owen Lovejoy's lab
00:53:42at Kent State University.
00:53:45To begin reassembling this intriguing creature on paper,
00:53:48they'll use the high-precision plaster casts
00:53:51of the Arte Pithecus skeleton.
00:53:54We take that piece and align it with that one.
00:53:57He is the equivalent of a supercomputer
00:54:00into which years and years of primate structure
00:54:03have been poured and recorded
00:54:06into what becomes an almost perfect image.
00:54:13Maternus begins his portraits of Arte
00:54:16by creating highly detailed drawings
00:54:19of each of the dozens of individual fossil casts.
00:54:22The fragments of her skull,
00:54:25her crushed pelvis, her grasping toe and hand bones.
00:54:28This staggering body of work
00:54:31amounts to hundreds of pieces of paleoart,
00:54:34each one precisely rendered at full scale.
00:54:45J.'s task also includes reconstructing on paper
00:54:48tissues that were never found.
00:54:53From bones to ligaments, muscles to skin,
00:54:56and finally to Arte's hair and eyes.
00:54:59My part of it is to interpolate
00:55:02between what is there
00:55:05and what is missing,
00:55:08and also to correct for any distortion.
00:55:13We have only one cervical vertebra.
00:55:16Nothing has remained of the scapula.
00:55:19So we had to infer that from modern humans and apes.
00:55:23The science team guides J.
00:55:26on how best to fill in gaps
00:55:29between the recovered bones.
00:55:32Gradually, his drawing of Arte's skeleton
00:55:35begins to take shape.
00:55:38Because of his artistic skills
00:55:41and because of his anatomical knowledge,
00:55:44we can take something like a partial foot
00:55:47and look at that foot,
00:55:50describe and interact with him
00:55:53as to what's present, what's missing,
00:55:56and then based on our joint anatomical knowledge,
00:55:59replace the missing parts.
00:56:02Literally hundreds of e-mails
00:56:05fly back and forth between artist and scientist,
00:56:08many with revised anatomical drawings attached.
00:56:11We've gone through drawing after drawing after drawing
00:56:14as we discovered additional aspects
00:56:17of the skeleton,
00:56:20as Tim cleaned more and more parts of it,
00:56:23and as Tim and Gen and I
00:56:26completed the reconstruction of the various parts.
00:56:29Each time that we did that, it changed a bit.
00:56:33At Kent State University,
00:56:36Lovejoy reviews J.'s latest drawings.
00:56:39Good.
00:56:42It was the expanded version of the skeleton
00:56:45with the expanded rib cage.
00:56:48The shoulders have been elevated
00:56:51over the previous version.
00:56:54The hamulus was much too big, but you have to mirror image.
00:56:57Now if you put the new one down,
00:57:00it's much more grass-out as it should be.
00:57:03Much more appropriate.
00:57:06The thumb looks small because the phalanges are so long.
00:57:09Yes, the thumb is astonishingly small.
00:57:12I mean, it's just full of surprises.
00:57:15So it's a very odd-looking creature
00:57:18and remarkably non-chimpanzee-like.
00:57:21Every bone and joint is carefully examined
00:57:24to ensure the accuracy of Artie's skeletal portraits.
00:57:27Trapezoid.
00:57:30What's the next step, do you think?
00:57:33The next step would be
00:57:36to put a skin on her
00:57:39with all the trimmings,
00:57:42hair and eyelashes and such.
00:57:45I taped it together here.
00:57:48Maternus would work for over 2 years,
00:57:51adding muscle and skin to Artie's body.
00:57:54...to envision what she might have looked like.
00:57:57Far from Ethiopia,
00:58:00far from the back-breaking field work in the Middle Awash
00:58:03and the long nights pouring over shattered fossils,
00:58:06Artie's portraits are now completed
00:58:09in a quiet Virginia studio.
00:58:15Drawn in charcoal,
00:58:18this fusion of art and science
00:58:21resurrects this creature from the inside out,
00:58:24from her skeleton to her muscles,
00:58:27and finally to her outer features,
00:58:30her face and her eyes.
00:58:34With her long arms and grasping big toes,
00:58:37Artipithecus finally emerges
00:58:40from the shadows of deep time.
00:58:43Artipithecus was a biped,
00:58:46but a very primitive biped,
00:58:49a biped that could grasp with its foot.
00:58:52That's different from any other mammal
00:58:55that's ever been found.
00:58:59But what would this strange bipedal animal
00:59:02with grasping feet have looked like when it walked?
00:59:05Discovery Channel filmmakers
00:59:08have come up with a strategy to find out.
00:59:11They'll use digital tools
00:59:14developed by Hollywood Studios
00:59:17to help visualize how Artie might have moved
00:59:20through her ancient world.
00:59:24Artipithecus seems to be a paradox,
00:59:27a bipedal hominid with a grasping foot
00:59:30and a chimp-sized brain.
00:59:33Here we have a creature
00:59:36that was unanticipated by science.
00:59:39The evidence for it could only have come
00:59:42from the fossil record.
00:59:45Artie's skeleton reveals a strange new creature,
00:59:48one that walked on 2 feet,
00:59:51but odd feet they were.
00:59:58But one of the interesting things
01:00:01that we have to deal with,
01:00:04and the most difficult, is the foot.
01:00:07And at first we thought this thing
01:00:10has a kind of free, great toe.
01:00:13The process of recreating Artie's movements
01:00:16begins at a company in Southern California
01:00:20that has spent years building up
01:00:23extremely sophisticated programs
01:00:26that can simulate human motion.
01:00:29So we're lucky because the creature
01:00:32that we're looking at has many elements
01:00:35in common with modern humans.
01:00:38One of the problems that we've got
01:00:41is how to recreate in a way
01:00:44that will fit the model.
01:00:47Interaction with computers
01:00:50is Life Modeler's specialty.
01:00:53These models simulate the dynamics
01:00:56of muscles, bones, and joints.
01:00:59This one is being used
01:01:02to help a prosthetics company
01:01:05design a knee replacement.
01:01:08Life Modeler also works with athletes
01:01:11to help improve their performance.
01:01:14We can take Artie's tennis
01:01:17and recreate that with a biomechanics
01:01:20simulation model and retrieve
01:01:23a lot of information from that.
01:01:26So what would happen
01:01:29if this same technology was applied
01:01:32to Artie's very unusual feet?
01:01:35Lovejoy wants to work with Life Modeler
01:01:38to see if they can simulate
01:01:41We can take those data
01:01:44that we've derived from the skeleton
01:01:47and from Jay and from Gan
01:01:50and put them all together
01:01:53and give them to Life Modeler.
01:01:56We know what elements are shared
01:01:59and what elements are not shared
01:02:02between Ardipithecus and modern humans.
01:02:05So they can take their programming,
01:02:08But this 4.4 million-year-old foot
01:02:11is not like anything Life Modeler has ever seen.
01:02:14With guidance from Lovejoy,
01:02:17Sean's team will need to modify
01:02:20their human model to match Artie's unique anatomy.
01:02:23We can test things like grasping function,
01:02:26which you're seeing right now.
01:02:29And so what we have here is a mixed function.
01:02:32We have a foot that has to be grasping
01:02:35the arboreal environment in trees,
01:02:38but then revert to towing off and walking.
01:02:41The second metatarsal is essentially
01:02:44the center axis of the foot,
01:02:47and it's the major propelling element
01:02:50of the foot in this animal.
01:02:53It's not in humans, and it's not in chimpanzees.
01:02:57This is a totally unique animal.
01:03:00This model will help the scientists
01:03:03see how Artie might have walked upright
01:03:06despite her grasping toe.
01:03:09Seeing Artie's legs move is one thing,
01:03:12but what about the rest of her body?
01:03:15If we could go back in time
01:03:18into that ancient African woodland,
01:03:21what would Artie have looked like?
01:03:24To find out, Lovejoy and Discovery Channel filmmakers
01:03:27will combine Maternus's drawings
01:03:30of Artie's skeleton
01:03:33with life modeler's simulations
01:03:36and then apply some Hollywood technical magic.
01:03:42The process about to begin is called motion capture.
01:03:45It's used by feature filmmakers and video game producers
01:03:48to create digital characters that move like real humans.
01:03:52But we do only articular surfaces.
01:03:55Since there is no living analog for Artipithecus,
01:03:58Lovejoy will use the next best thing,
01:04:01Jade Kwan, a stuntwoman who is about Artie's size.
01:04:04After the session,
01:04:07Jade's proportions will be adjusted
01:04:10to exactly match Artie's.
01:04:13Yeah, so hold me a little.
01:04:16That's why I keep looking at that thing over there.
01:04:19Jade's suit is studded with reflective markers.
01:04:22Her motion is captured by an array of 120 cameras
01:04:25connected to a bank of computers
01:04:28designed to capture her every movement
01:04:31from every possible angle.
01:04:34Because you're going to be walking and not running.
01:04:37I notice that you don't have to bend the knees so much.
01:04:40Yeah, I'm trying to stay.
01:04:43Lovejoy will coach Jade through the session
01:04:46using his extensive knowledge of Artie's anatomy and habitat.
01:04:49And T-pose please, roll cameras, and we're rolling.
01:04:52Now walk really fast.
01:04:58Jade's movements are translated into data in real time.
01:05:10Oh, that was a good take.
01:05:13We can do that as a separate take or something.
01:05:16The foot that we're looking at in Artipithecus
01:05:19is a different analogy.
01:05:22There's nothing like it.
01:05:25But there are elements of our own hands and our own feet
01:05:28in terms of motion patterns that we can combine
01:05:31and in that way achieve something
01:05:34that looked like the Artipithecus foot motion.
01:05:37Now work can begin
01:05:40on building the fully detailed computer animation.
01:05:44To complete the process,
01:05:47the animation team will have to add one final dimension,
01:05:50the living world that surrounded Artipithecus
01:05:53as she walked some 4.4 million years ago.
01:06:06The hard fossil evidence is now in hand.
01:06:09But it seems to pose
01:06:12more questions than answers.
01:06:17Artipithecus' brains were small,
01:06:20the size of a chimpanzee's.
01:06:23Their big toes allowed their feet
01:06:26to grasp tree branches.
01:06:29But their short palms and flexible wrists
01:06:32show that these creatures never walked on their knuckles
01:06:35as chimps do today.
01:06:39The shape of the pelvis confirms
01:06:42that Artie was some kind of early biped.
01:06:49Since the time of Darwin,
01:06:52two fundamental questions in human evolution
01:06:55have challenged researchers.
01:06:58How and why our ancestors began to walk habitually
01:07:01on two legs?
01:07:09The Artipithecus discovery now represents
01:07:12the earliest hominid skeleton.
01:07:15But Artipithecus is a creature so new,
01:07:18so unexpected, that visualizing it is difficult,
01:07:21even for the scientist.
01:07:27So Discovery Channel filmmakers will use digital animation
01:07:30to try to bring Artie back to life.
01:07:38Motion capture sessions in Hollywood have provided data
01:07:41to help animate a digital Artie.
01:07:49Now the detailed anatomical drawings
01:07:52created by Jay Matournas are transformed
01:07:55into three-dimensional digital images.
01:07:59After months of work,
01:08:02motion capture data are finally applied
01:08:05to a unique digital skeleton.
01:08:08Placing Artie's body into her lost world
01:08:11will be the final step.
01:08:14The artists are relying on evidence
01:08:17from the grueling fieldwork done at Aramis
01:08:20to fill in details of the natural environment.
01:08:28This mountain of data is used to digitally recreate
01:08:31the woodland environment of Artipithecus.
01:08:35The final step is to incorporate the digital Artie.
01:09:05When we first see Artipithecus, it's striking to us
01:09:08because here's an animal that truly is primitive
01:09:11and yet it's embarked upon a career of walking bipedally.
01:09:17Bipedality is so common to us,
01:09:20it is so second nature,
01:09:23that we tend to think it's a very natural form of locomotion.
01:09:28It is in fact a very strange and odd form of locomotion.
01:09:36Roughly 7 billion of us live on the planet today,
01:09:39with over half that number settled in towns and huge cities.
01:09:46It seems like humans are everywhere,
01:09:49so we seldom stop to reflect
01:09:52on what truly odd mammals we are
01:09:55or question the truly weird way that we walk.
01:09:59If you go to New York
01:10:02and walk the streets of New York,
01:10:05you look around and you don't think anything about the fact
01:10:08that these are all erect walking bipeds.
01:10:11And yet this form of locomotion
01:10:14is absolutely unique in the animal kingdom.
01:10:23As we track humans back through time into the fossil record
01:10:26and all of our individual special characters
01:10:29begin to drop out, when you get to the very bottom,
01:10:32it is simply bipedality
01:10:35that becomes the defining character of being human.
01:10:40Bipedality is traditionally the hallmark of being human.
01:10:47So the very definition of humanity
01:10:50or the family name Hominidae was defined
01:10:53by the fact that our earliest ancestors
01:10:56were able to walk on two legs.
01:11:01For scientists, bipedality has always seemed
01:11:04the most puzzling part of human biology.
01:11:12It's a terrible form of locomotion.
01:11:15So you're forced into the question,
01:11:18why did this animal ever adopt
01:11:21this peculiar form of getting around?
01:11:27No other mammal has ever become a bipedal walker,
01:11:30and for a very good reason.
01:11:33A four-legged animal has far more speed and agility,
01:11:36while slower bipeds would have been
01:11:39easy meals for hungry carnivores.
01:11:44There's no shortage of ideas
01:11:47about why bipedality evolved in hominids.
01:11:50For decades, bipedality was thought to have evolved
01:11:53when hikers moved into the grassland savannas of Africa.
01:11:56But the evidence now shows
01:11:59that Ardipithecus was a biped
01:12:02who lived and died in a woodland, not a savanna.
01:12:08Most theories about walking on two legs
01:12:11have focused on a single, isolated advantage,
01:12:14like the ability to reach up and pick fruit,
01:12:17look over tall grass,
01:12:20and adopt a threatening pose.
01:12:23Bipedality in and of itself
01:12:26could not solve any particular simple issue.
01:12:29It must have been part of a larger
01:12:32and more important adaptation.
01:12:35And that's the mystery of human evolution,
01:12:38is figuring out what that adaptation was.
01:12:41It's now clear that millions of years ago,
01:12:44bipedality did evolve in our African ancestors.
01:12:47Being upright must have provided
01:12:50some huge biological advantage for the earliest hominids.
01:12:53Bipedality was a positive
01:12:56that outweighed all the negatives.
01:12:59What advantage did it bring to our early ancestors?
01:13:08In the evolutionary sweepstakes,
01:13:11Darwin knew the winning ticket
01:13:14was the ability to reproduce as humans have.
01:13:17Our closest relatives, the great apes,
01:13:20have not kept up,
01:13:23and today they're on the brink of extinction.
01:13:28Gorillas and chimps occupy
01:13:31little pockets of Miocene forest,
01:13:34but they're not successful.
01:13:37They're on the decline.
01:13:40While hominids are all over the world,
01:13:43they're enormously reproductively successful,
01:13:46and what that signifies
01:13:49is they must have undergone a major shift
01:13:52in reproductive strategy.
01:13:55An intriguing clue to that shift in reproductive strategy
01:13:58would come from the many fossil teeth found at Aramis,
01:14:01just the evidence investigators needed.
01:14:04Males of all living and fossil apes
01:14:07share one very distinctive trait.
01:14:10In order to compete with one another,
01:14:13they have very large projecting,
01:14:16what are called honing or sharpening canines.
01:14:19The upper and lower canines, when they occlude against each other,
01:14:22actually sharpen to keep them
01:14:25in excellent shape as aggressive tools.
01:14:32Canine teeth from many Ardipithecus individuals
01:14:35were found at Aramis,
01:14:38but Ardipithecus' teeth were small and blunt.
01:14:41Because all living and fossil male apes
01:14:44have large, sharp projecting canine teeth,
01:14:47it's likely that our distant ancestors also had them.
01:14:50But Ardi did not.
01:14:53Even the largest male canines
01:14:56in the Ardi species were very small
01:14:59compared to any fossil or modern ape.
01:15:02Ardipithecus had seen canine reduction.
01:15:08At 4.4 million years ago,
01:15:11Ardipithecus had evolved two big changes,
01:15:14bipedality and smaller male canines.
01:15:17Taken by themselves,
01:15:20either change would seem to be a huge disadvantage.
01:15:24So we're faced with putting
01:15:27those two critical clues together
01:15:30and explaining it somehow.
01:15:33What could walking on two legs
01:15:36have to do with the small canine teeth
01:15:39in these earliest hominids?
01:15:42One possible explanation comes from studies
01:15:45of primate behavior and anatomy.
01:15:48In Ardipithecus, the canines have dramatically reduced,
01:15:51and this tells you that somehow
01:15:54there's been a major change in social behavior.
01:15:57In all other primates,
01:16:00males use their canine teeth as weapons
01:16:03to communicate with each other.
01:16:06They fight over females
01:16:09who show visible signs that they're ovulating.
01:16:12Male Ardipithecus canines
01:16:15are greatly reduced, like ours.
01:16:18If male canines are reducing,
01:16:21it means that females
01:16:24are choosing males with smaller canines.
01:16:27What could a male be doing
01:16:30to make a female want that,
01:16:33to have the offspring of that male
01:16:36rather than those of a more competitive, more aggressive male?
01:16:39One possible answer is that by pairing with males
01:16:42who were dependable sources of food,
01:16:45females had more time and energy
01:16:48to devote to their youngsters
01:16:51and to have more of those offspring during their lifetimes.
01:16:54This is what winning
01:16:57evolutionary sweepstakes is all about,
01:17:00reproduction and survival.
01:17:06The formation of what scientists call a pair bond
01:17:09between males and females
01:17:12would have been based on the exchange of food and sex.
01:17:18With this kind of system,
01:17:21males could have foraged separately
01:17:25The all-important reproductive advantage
01:17:28would have gone to those males who collected and carried
01:17:31high-value foods to their mates
01:17:34and their dependent young, whom they likely fathered.
01:17:37Natural selection would have favored those
01:17:40who could walk farther on two legs,
01:17:43carrying food more effectively.
01:17:46Males with smaller canines,
01:17:49pair bonds reinforced by regular sex,
01:17:52carrying and sharing of food.
01:17:55Could these be the keys to the evolution of bipedality?
01:17:58To the evolution of us?
01:18:01Better bipeds would have been better able to carry food
01:18:04and carrying food would have given
01:18:07the earliest bipeds a big reproductive advantage.
01:18:13If this model is correct,
01:18:16then bipedality was the breakthrough
01:18:19and the foundation of our mating practices
01:18:22and sexual biology.
01:18:25So it turns out that the long-sought keys
01:18:28to our species' success and the basis of our unique
01:18:31sexual biology are all tied up
01:18:34with the strange way that we walk.
01:18:37We humans are not just the most unusual primate,
01:18:40we are arguably the most unusual mammal
01:18:43on planet Earth.
01:18:46Ardipithecus, a 4.4 million year old
01:18:49woodland biped with small blunt canine teeth,
01:18:52hints that much of our unique
01:18:55sexual anatomy and physiology,
01:18:58even our families and the way we walk
01:19:01may all be fundamentally linked
01:19:04and far more ancient than we ever imagined.
01:19:08The fossil evidence now suggests
01:19:11that the things that make humans so different
01:19:14from all other mammals are not recent
01:19:17but can be traced all the way back
01:19:20to Ardipithecus.
01:19:30Ongoing discoveries in Africa are now bringing us
01:19:33even closer to the roots we share with the rest
01:19:36of the natural world.
01:19:39But this journey into our past is far from over.
01:19:44Now, discoveries of fossils even older
01:19:47than the ones at Aramis have been made
01:19:50in the badlands nearby.
01:20:02We humans have literally changed the face of our planet,
01:20:05so much so that often it's hard to imagine
01:20:08that we're part of the natural world.
01:20:15But the ancient fossils discovered in Ethiopia
01:20:18have taken us beyond imagination
01:20:21to knowledge based on hard evidence.
01:20:45That discovery, Ardipithecus ramidus,
01:20:48has opened a new window on the origins
01:20:51of our unique human biology
01:20:54and where and why this biology evolved in the first place.
01:21:02But are there even older hominid fossils out there
01:21:05waiting to be found?
01:21:08Surely there's no better place to look
01:21:11than here in Ethiopia.
01:21:14But the really unique thing about our study area
01:21:17of the Middle Awash here in Ethiopia
01:21:20is it's given us a much longer sequence of human evolution
01:21:23in the form of snapshots at different time planes.
01:21:26So not just one fossil now,
01:21:29but a series of hominid fossils like a time-lapse film
01:21:32chronicling how the human lineage changed across deep time.
01:21:36Even while the Middle Awash team was extracting Ardipithecus
01:21:39from the sediments at Aramis,
01:21:42project scientists were busy elsewhere in the study area,
01:21:45probing more deeply in time
01:21:48in search of Ardi's ancestors.
01:21:54Paleoanthropologist Yohannes Haile-Selassie
01:21:57and geologist Gide Wolde-Gabriel
01:22:00were searching an area to the west of Aramis.
01:22:06Here, the sediments are more than a million years older.
01:22:13After years of searching,
01:22:16the Ethiopians made a new and significant find,
01:22:19fossils that would be dated at 5.7 million years old,
01:22:22among the oldest hominids ever found.
01:22:30Here, in the searing heart of Ethiopia's Afar Depression,
01:22:34the scientists have found hominid teeth and bone fragments
01:22:37more than a million years older than the Ardi skeleton.
01:22:45They named these new fossils Ardipithecus kadaba.
01:22:48In the local Afar language,
01:22:51kadaba means ancient father.
01:22:57This find, along with others from Chad and Kenya,
01:23:00are still very fragmentary.
01:23:06So far, there's no skeleton for this early time period,
01:23:09but the search goes on.
01:23:15So with these discoveries,
01:23:18we're pushing our evolutionary history
01:23:21back to about 6 to 7 million years ago,
01:23:24and we're not done yet.
01:23:27We are an ancestor between chimpanzees,
01:23:30who are our closest relatives, and ourselves.
01:23:36With a new generation of African scientists
01:23:39at the forefront of this research,
01:23:42this vast continent will continue to produce
01:23:45new and important fossil discoveries.
01:23:53I'm very, very proud of the Middle Awash Project
01:23:56that discovered a lot of fossils.
01:23:59It has trained a lot of Ethiopian and American professionals
01:24:03and still training more young generation
01:24:07from both the U.S. and Ethiopia.
01:24:15Being a paleoanthropologist is all about
01:24:18being able to find the fossils, analyze them,
01:24:21prepare them, clean them, analyze them, study them,
01:24:24and share the knowledge that you get out of these fossils
01:24:27with the rest of the scientific community
01:24:30and the public, the general public.
01:24:33For years to come, scientists from around the world
01:24:36will sift through fossil evidence
01:24:39gathered during the decades of research
01:24:42by the Middle Awash team and other groups as well.
01:24:45But why are these discoveries important today?
01:24:48Virtually every culture on Earth has its own origins myth,
01:24:52and in fact, these origin myths are people's stories
01:24:55about how the world was formed and how they got on the world.
01:24:59But now we can move beyond myth. We can move beyond fairy tale.
01:25:03We can move, guided by evidence,
01:25:06to what really happened in our past.
01:25:12A century and a half ago, Darwin's critics
01:25:15pointed to the huge differences between living apes and humans
01:25:19as evidence of a fatal flaw in his theory that humans evolved.
01:25:24Cartoonists at the time satirized Darwin
01:25:27as a deluded, half-chimp, half-human creature.
01:25:35More than a century later, a real creature,
01:25:38recovered from a small hill in Ethiopia,
01:25:41has brought the hard evidence Darwin lacked.
01:25:44Ardipithecus has finally removed the barrier
01:25:48once thought to separate us from the rest of the living world.
01:25:55And in this valley, we have found our roots.
01:25:58We've been able to trace those roots for 6 million years into the past
01:26:02and to put together a record of human evolution
01:26:05that is not only comprehensive,
01:26:07it's also very clear and is very compelling.
01:26:10We evolved.
01:26:12Evolution has produced a tree filled with branches,
01:26:16not a chain of links.
01:26:19Today, Homo sapiens is just one twig
01:26:22on life's vast and spreading tree.
01:26:28Even though Ardipithecus lived far back
01:26:31along our branch of the family tree,
01:26:34it already had important traits found today only in our species.
01:26:41Ardipithecus shows that we did not evolve from chimpanzees.
01:26:46And it also reveals that we were not created
01:26:49apart from the rest of life on Earth.
01:26:52We humans evolved as part of the natural world,
01:26:55just like all other animals.
01:27:01Today, our technology is driving thousands of plant and animal species
01:27:05to extinction and changing the climates of our planet.
01:27:10Now, 4.4 million years after Ardi walked the Earth,
01:27:14we humans are facing our greatest challenge,
01:27:18to help return to balance the world that we have changed.
01:27:39Transcription by ESO. Translation by —