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Documentary, BBC - Horizon - 2001 - The Ape that Took Over the World
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00:00It's long been known that millions of years ago, one special creature walked here.
00:13These are fossilized footsteps from the dawn of mankind, the oldest footprints made by a human
00:21ancestor. For years, scientists have been convinced that whatever creature walked here
00:28would hold the key to the biggest mystery in all evolution. Why it is that human beings have evolved
00:35to be so different, so unlike all other animals. Now, a new discovery may just provide the answer
00:44to that question. The trouble is, it is not what anyone had expected. When I first saw this fossil,
00:51I realized it was going to really change your ideas of human evolution.
00:58It is a change of such importance that the story of how man rose up from the apes and
01:04came to rule the world may now have to be rewritten.
01:28In this secret vault in Kenya, they keep human history under lock and key. Here, they guard
01:39the most precious fossils in the world, the fossils that tell the story of our evolution.
01:47And there is one fossil here, more remarkable than all the others. Found just recently, it
01:58is of a human ancestor like no other.
02:02We didn't realize how different it was until we began comparing in the museum. And that was
02:07a very exciting time, because we waited such a long time to have the specimen prepared.
02:13And then, when we got to study it, and we kept taking something else out of the cupboard
02:17and comparing it, it was different, and this was different, and that was different.
02:22Meeve Leakey and her team spent a whole year painstakingly assembling their discovery from
02:27just tiny fragments. And as they analyzed it further, the more baffled they became. This
02:38fossil didn't fit into any known pattern of human evolution.
02:42We just simply couldn't find something that looked really similar. Quite quickly, we began
02:48to realize we had something very, very different. And then, of course, it was a matter of saying,
02:52well, okay, to have something different, but which group does it fit in? It must fit with
02:56something that's already known. And then it didn't seem to work that way either. And so,
03:02in the end, we realized that we did have something that was unknown. It was new.
03:11They had put together a skull, the oldest skull ever found of a human ancestor. When word
03:18of this discovery spread, science was faced with something stunning. Because this fossil
03:25skull should not exist. Because of it, a mystery that many in science thought had been solved,
03:33will have to be reopened. For this skull says that a key part of the theory of how human beings
03:41evolved from apes and came to dominate the planet has all been based on a mistake.
03:48The big mystery of human evolution began 10 million years ago, when the earth was a very different
03:57place, far more lush and tropical than it is today. Back then, one kind of creature reigned supreme.
04:03The apes. They were everywhere. The earth really was the planet of the apes.
04:10These were apes like we can barely imagine. There were 50 different species of them, and they
04:17roamed right across the planet. There was the huge Sivapithecus in the jungles of the east.
04:23It was twice the weight of a man. There was tiny Limnopithecus that lurked high in the forest canopy, eating fruit no other creature could reach.
04:30This world was an apes' paradise. For the apes living some 10 million years ago, in the past 10 million years ago, the apes were
04:37grown in the wild forest. With the wild forest, they were very different and they were very different.
04:39They were very different, and they were very different. The wild forest was around the forest.
04:40They were very different. There were many different species of them, and they roamed right across the planet.
04:43There was a huge Sivapithecus in the jungles of the east. It was twice the weight of a man.
04:45There was tiny Limnopithecus that lurked high in the forest canopy, eating fruit no other creature could reach.
04:49This world was an apes' paradise.
04:55For the apes living some 10 million years ago, it was really a great time because we had an enormous variety of different types of apes. Those living more in the trees, those living more on the ground. There were very big apes and there were smaller apes. And it must have been really an exciting time.
05:18Apes were the most intelligent animals alive at the time. They may even have used sticks and stones as tools to get food. But then the fossil record shows the planet of the apes just stops.
05:34All this enormous variety of different types of apes disappeared about some 7, 8 million years ago. And we really cannot find an exact explication why this happened.
05:52Seven million years later, there are just a few survivors from the planet of the apes, like the orangutan, the gorilla and the chimpanzee.
06:04And in place of all those apes is an animal clearly related to them, but which could not be more different. Human beings.
06:13No other creature has ever thought like us, built like us, dreamed like us.
06:26We are more intelligent than any other animal there has ever been.
06:39We alone can aspire to understand the deepest mysteries of the universe. We alone can hope to control nature itself. We are light years ahead of anything that has ever lived before.
06:54We choose to go to the moon in this decade and do the other things. Not because they are easy, but because they are hard.
07:07That's one small step for man, one giant leap for mankind.
07:13This gulf between us and all other creatures is so huge that long ago it convinced scientists that we must have been produced by an evolutionary process that was different from all other animals.
07:28In some way we had been chosen.
07:35But what had made us evolve into something so unique? What evolutionary development had allowed us to become so vastly more intelligent than all other animals?
07:46That was the great question the disciples of Charles Darwin, evolution's founding father, were left with.
07:56The answer, early anthropologists thought, would lie out there in the rocks.
08:03Somewhere there would be a fossil that could explain it all.
08:08It would be a fossil of an animal that was basically an ape, but which showed the first key human characteristic to have evolved.
08:17It was believed that that first key characteristic would prove to be the thing that had made us so superior to all other animals.
08:26And of all the evolutionary changes between humans and apes, one dwarfs them all.
08:34Our brains have grown to an extraordinary size, and this bewitched early anthropologists.
08:41Humans have very large brains and our cranial capacity is about 1400 cubic centimeters.
08:46In this contrast to the chimpanzees that are around 400 cubic centimeters.
08:51So humans are three times the size of a chimpanzee brain.
08:55And so, over a hundred years ago, the big brain theory of human evolution was born.
09:01It seemed obvious that our special evolutionary process must have begun with the development of our superior intelligence.
09:08According to the theory, in the last seven million years, an ape must have evolved to have a slightly bigger brain.
09:16This more intelligent ape would have given birth to a line of progressively bigger-brained super-apes, who ultimately turned into humans.
09:26When we're looking at human evolution, what we have to realize is that we define ourselves by our big brain and by everything that results from that big brain.
09:36And for many years, paleoanthropologists have felt that that was what we're looking for, that the most important period in human evolution is when we see that big brain, that somehow this defines our species.
09:49The big brain theory dominated early anthropology. All they needed was the fossil to prove it.
09:56It turned the quest to find the fossil with the first key human characteristic into the quest for the fossil of an ape-like animal with a big brain.
10:06The only question was, how would they know when they had found it? How big would its brain have to be to make it our ancestor?
10:19One man who thought he knew the answer was one of anthropology's legends, Lewis Leakey.
10:28Leakey set what he called a cerebral rubicon.
10:32By pouring beads into a skull's brain cavity and then measuring the volume of the beads, it is possible to estimate brain size.
10:45Leakey said the fossil they were looking for would have a brain bigger than that of any known ape, but about half that of a human's, measured in cubic centimeters.
10:57Leakey and anthropologists were trying to define what the first human would be like.
11:01And they set a value for brain size that was outside the range of any known ape.
11:06And they settled on a figure of about 600 to 700 cubic centimeters.
11:12Leakey looked in Africa for 50 years.
11:17He found bones of ancient apes.
11:20He even found a skull, but its brain was below the 600 cubic centimeters needed for it to be the elusive ape with the big brain.
11:28The ape that had set us out on our unique evolutionary path.
11:32But all the while he knew it had to be out there in Africa, somewhere just waiting for him to find it.
11:41By the 1970s, Lewis Leakey was an old man with failing health.
11:47It was time for someone else to take up the quest.
12:02The call was answered by Lewis's son, Richard, and his wife, Meve.
12:07They sent teams scouring the rocks of Kenya, looking for the elusive fossil of the ape with the big brain.
12:18That key characteristic that scientists believe triggered the amazing evolution of human beings.
12:24Then, after searching for four years, they saw something peeping out from the rocks.
12:42It was just a few fragments sitting on the surface that really didn't look like anything.
12:48And, in fact, the field crew had noticed it and looked at it and thought that it was bits of an antelope.
12:53This bit of an antelope was dated at around 2.8 million years old.
12:59Halfway between the present day and the end of the planet of the apes.
13:04The perfect age for the key development that had separated humans from apes to have happened.
13:10And there was something about this fossil that intrigued Richard Leakey.
13:15And so he began trying to put the pieces together.
13:18After about a week of Richard not doing a very good job, I have to say,
13:22they got bored with it and said, OK, you have a go.
13:26It was a task that Meve Leakey had never attempted before.
13:30And so over the next few weeks, I had a wonderful time trying to stick all these pieces together.
13:36And I think it was definitely one of the most challenging and exciting jigsaw puzzles I have ever done.
13:41And it gradually came together.
13:43It was not the skull of an antelope, but of an ape-like creature.
13:51And it seemed to have an unusually large brain.
13:55The question was, did it cross the magical cerebral rubicon, 600 cubic centimetres?
14:03They couldn't wait to get it back to Nairobi and to do it properly.
14:06So they decided to fudge it in camp using whatever they had.
14:10And they didn't have very much.
14:11So what they did was they filled the cranium with sand.
14:14And then they poured the sand into a rain gauge.
14:17And they measured the amount of sand that filled the cranium vault.
14:20And it came to eight inches of rain, which they estimated was to be about 800 cc, which is pretty close.
14:27I think now it's 785 or something like that.
14:30Richard Leakey believed he had done it.
14:33He thought he had found the fossil his father had been looking for.
14:37So there was one person he just had to tell.
14:40Richard said, well, I really want to take it to Nairobi because I want to show my father.
14:44And so he flew back to Nairobi with it to show Lewis.
14:48Lewis was very excited when he saw the specimen.
14:51And it was a great moment, I think, for both of them.
14:54Two weeks later, Lewis Leakey died.
14:59The skull, now known simply by its museum classification number 1470,
15:05seemed to have fulfilled his life's quest.
15:08To find the fossil of the ape with the big brain.
15:11The fossil that seemed to prove humans had evolved in their special way
15:15because of the early development of their intelligence.
15:181470 was a sensation.
15:25Reconstructed all over the world so that everyone could gaze upon this crucial human ancestor.
15:32It became more than just a fossil, but an icon.
15:36Because here seemed to be proof of what had always seemed so obvious.
15:41That it must be our superior intelligence that had set us apart from all other animals.
15:47And the first key evolutionary change that had begun it all must have been the development of the big brain.
15:54So here seemed to be evidence for what you can think of as the sort of brain led theory of human evolution.
16:00That we have a large brain early on in the course of human evolution.
16:04And in a sense, once you have a large brain, everything else is inevitable.
16:08And this seemed to show exactly that pattern.
16:11It now seemed beyond doubt that human beings had evolved in their unique way because of the big brain.
16:21But this whole theory was about to be proved wrong.
16:26The triumph of Leakey and 1470 was to be short-lived.
16:42In 1974, a young American researcher called Don Johansson was hard at it in the field,
16:49looking in rocks that were about the same age as 1470.
16:53I was out surveying in the morning with one of my graduate students, Tom Gray.
16:57And as we were walking back to the Land Rover, it was now noon time and it was,
17:01well, it was close to 110 degrees and it was time to head back to camp.
17:05I happened to glance over my shoulder.
17:07And as I looked down, I spotted this piece of bone, a little piece of elbow.
17:14And as I looked up this slope, a very gradual slope, I saw, glistening in that sunlight, other pieces of bone.
17:23They had stumbled upon almost the entire skeleton of a three million year old ape-like creature.
17:30Here was a specimen that was astonishingly complete, something that really literally had never been found before.
17:38Round the campfire, they christened their new discovery.
17:43One night when we were celebrating, we were listening to a Beatles tape.
17:48And on that tape, Lucy in the Sky with Diamonds was playing.
17:52And a member of the expedition said, well, why don't we just call the skeleton Lucy?
17:58Back in America, they began to analyze Lucy.
18:05She was classified as an Australopithecine, an ape-like creature, and was dated at about 3.2 million years old, just older than 1470.
18:17But then, as they slowly put the bones together, there came proof that she really was a human ancestor.
18:32Because this ape-like creature had one clear human characteristic, and it wasn't a big brain, but something quite different.
18:42She seemed to walk in a way that only humans do.
18:45Lucy was, as scientists say, bipedal, unlike apes who are quadrupedal.
18:51She walked on two legs, not four.
18:55Fortunately, we had most of her pelvis preserved, which of course is a critical part in terms of how an animal locomotes.
19:04For example, a quadrupedal, a four-legged chimpanzee, this example, for example, is very different from what we see in Lucy's pelvis.
19:14And in many respects, not identical, but in many aspects, Lucy's pelvis reminds us of our own.
19:23Here is a pelvis of a modern human walking on two legs.
19:27And the similarities are quite striking.
19:30No mammals, apart from humans, have ever walked on two legs.
19:35And there was more.
19:39They found Lucy's footprints.
19:43The fossilized Lytoli footprints were discovered in northern Tanzania in 1976.
19:49They are 3.6 million years old, almost the same age as Lucy, and were just the same size as her feet.
19:57They seemed to confirm that Australopithecines like Lucy had walked on two legs.
20:04We are looking at the soft anatomy of early human ancestors who walked across a volcanic ash and left an impression of what their feet looked like.
20:15We see that their feet were shaped just like ours, that they walked around in a manner that was almost identical to ourselves.
20:23If Lucy had walked on two legs, then it seemed she had to have been a human ancestor.
20:29And that's when the trouble started, because Lucy's brain was just too small.
20:35Fortunately, we had the very back portion of the skull preserved.
20:44And you can tell from the curvature and the size of a brain that would have fitted in there, that it was about the size of an American softball,
20:53which means about a third to a fourth the size of a modern human brain.
20:58So this was a creature with an ape-sized brain, very different from our own.
21:04There was now a huge problem.
21:08Only one of Lucy and 1470 could be our ancestor.
21:13Both were about three million years old, but each had different characteristics, unique to humans.
21:19If the theory was right, and it really had been the development of our masterful intelligence that had led us to evolve from apes,
21:29then that ancestor had to be the big-brained 1470.
21:33But now there was real doubt.
21:38The signal that was coming out of these fossils was difficult to interpret,
21:42because on the one hand you had 1470 with its very large brain,
21:47and on the other hand you had Lucy with a very small brain, but clearly bipedal.
21:55And so what we then had was really a period of conflict.
22:00The only compromise, that somehow the slightly older Lucy had evolved into 1470, was also ruled out.
22:081470's brain was twice the size of Lucy's.
22:11There was no way any creature could have doubled its brain size in the 400,000 years that separated them.
22:21The conflict was resolved brutally.
22:271470 and Lucy were dated again, using radioactive dating techniques.
22:36Both had been found between layers of volcanic rocks,
22:39and volcanoes produce radioactive minerals when they erupt.
22:43Over time these minerals decay.
22:46By working out how far this decaying process had gone,
22:49they calculated the age of the rocks in which the fossils were found.
22:56The result would change everything.
23:03Two-legged Lucy was just over three million years old,
23:07but big-brained 1470 was more than a million years younger.
23:12Less than two million years old.
23:15The leakers had blundered.
23:18The difference was such that 1470 could be descended from Lucy.
23:23And that meant the fossil of an ape-like creature with the first key human characteristic
23:28was not the big-brained 1470, but the two-legged, small-brained Lucy.
23:36The big-brained theory was now officially in the bin.
23:42Instead, hard though it was to believe,
23:45it was now clear that the first key human evolutionary development
23:49that had set human beings on their unique evolutionary path
23:53was that we had walked on two legs.
23:56It basically killed the old idea that the earliest ancestors would have a big brain.
24:01Because now we realize that bipedalism must have led into later ancestors with the larger brain size.
24:10Lucy now became the great iconic fossil.
24:13The creature that held the key to why human beings were so much more intelligent than all other animals.
24:20Though it was hard to see why walking on two legs had somehow made us the most intelligent beings on the planet.
24:29Why intelligence should have evolved from moving on two legs doesn't seem obvious.
24:39So now a theory had to be devised to explain how bipedalism had let us evolve into the most amazing creature on the planet.
24:53We suffer from back pain, fallen arches, hernias.
24:57We're very slow. We're one of the slowest mammals around.
25:00Think about the fact that here was a little three and a half foot tall Lucy walking around with lots of hungry carnivores.
25:07She couldn't outrun a house cat.
25:09So the advantages of bipedalism must have far outweighed the disadvantages.
25:14But then it all became clear to anthropologists.
25:18State one was that by standing up our front legs became hands.
25:24When our ancestors stood up they could begin to use their hands to carry things,
25:29to make and use stone tools, to manipulate things, to use them in ways that the quadrupeds don't.
25:36Tools led to early technology. Technology to more ways of getting food, better diet, fed bigger brains.
25:48This had enormous consequences for things like social organisation and language.
25:55And this was then the stimulus for the development of larger brains.
25:59Larger brains led to primitive culture and new ways of communicating.
26:08Better communication led to more complex societies, more complex societies to more advanced cultures and even bigger brains.
26:18And so it went on for millions of years.
26:21So there were ways in which two legs could lead to mankind's ancestors developing bigger brains.
26:30It seemed we had evolved into the most intelligent of all animals for one simple crucial reason.
26:36Because millions of years ago, Australopithecines like Lucy walked on two legs.
26:45But there seemed to be something even more extraordinary about Lucy.
26:49Something so remarkable that it confirmed what many had long believed.
26:54That in some strange evolutionary way, we really were unique.
26:59Because it began to seem that Lucy's species, alone of all creatures, had defied the laws of evolution.
27:14Lucy's species should have evolved according to laws of evolution,
27:18which state that major evolutionary events occur when there is a sudden and dramatic environmental change.
27:24Those who cannot adapt to the new world, die.
27:29But some animals will have a chance mutation that may help them survive in the new environment.
27:42These survivors will form the basis of a new species.
27:45Slowly, these new species will start to exploit all the different ecological niches in the new environment.
27:52Gradually, these creatures will adapt to these different niches,
27:56and slowly one new species will evolve into two.
27:59We can see how this happens where something new arises.
28:05There's a new adaptation, a slightly better way of getting hold of food, of avoiding a predator,
28:10of walking across a landscape.
28:13And that then gives that population an advantage.
28:16It spreads out into new areas.
28:18Where you had one population, you now have two.
28:21Where you have one species, you now have two species.
28:23This is how evolutionary family trees develop.
28:28Two species split to form separate branches.
28:31These branches can split again, and then again.
28:34And so a whole host of related species will develop.
28:38So what is happening is that each time you're getting proliferation of branches,
28:43you're getting divergence taking place, and with that divergence comes what we think of as an adaptive radiation.
28:51Adaptive radiation is one of the fundamental truths of evolution.
28:57There are signs of it in virtually every type of animal that has ever lived.
29:01Like the cat family.
29:13The cats are a beautiful example of an adaptive radiation,
29:15because you can see what they all have in common.
29:17They have in common the fact that they are hunters and stalking hunters,
29:22and they have diversified from a common ancestor into everything from lions,
29:28which are very large, to wild cats and lynxes that can live in cold environments,
29:33to indeed domestic cats today.
29:35So they are a beautiful example of this, the shape of evolution.
29:39Adaptive radiation has given cats a classic evolutionary family tree.
29:52Lots of related species coming from lots of different branches.
29:56It means the cat family tree has a distinctly bushy appearance.
30:01And tracing any individual creature's line of ancestors is a complex business.
30:07If Lucy's species had evolved like any other animal,
30:11her evolutionary tree should have the same bushy shape.
30:14There should be lots of two-legged creatures appearing just after the planet of the apes.
30:20But the fossil record seemed to show that the only signs of adaptive radiation came well after Lucy.
30:27All the fossils leading back from Lucy to the planet of the apes
30:31seemed to be just primitive versions of the same Australopithecine Lucy.
30:36It seemed that Lucy had evolved without any adaptive radiation.
30:42Our family tree appeared to have no related branches before Lucy at all,
30:47but was just a solitary straight line.
30:50And this defied the laws of evolution.
30:53One would expect to look at human evolution as an adaptive radiation,
30:59but the way it was always reconstructed was very much as a linear story.
31:03And I think that actually goes back to the idea of human uniqueness.
31:07People expected humans to evolve differently and uniquely and have a single line.
31:12It seemed to many that the old idea that humans were different from all other animals was right.
31:21Every other creature had followed the typical evolutionary pattern of adaptive radiation, except Lucy's species.
31:35She alone seemed to have emerged from a single elite line of super-creatures,
31:40so special they defied the laws of evolution.
31:56Then, thousands of miles from Africa, a chain of events began that would alter our whole attitude to Lucy
32:03Lucy and her species' extraordinary ability to defy the laws of evolution.
32:17Along came Jay Quaid.
32:19He couldn't care less about human evolution.
32:23He's a geochemist, an expert in the chemical composition of rocks.
32:33A few years ago, he was contacted by some baffled paleontologists.
32:38They had noticed something strange about fossils dating from between 6 and 8 million years ago.
32:44Fossils from the end of the Planet of the Apes.
32:48A whole swathe of animals, not just the apes, seemed to disappear.
32:53And they all had one thing in common.
32:56They lived in the same environment.
33:00Starting about 8 million years ago, what was disappearing were animals that they believed were specific to a forested habitat.
33:08Tree-dwelling orangutans, tree-dwelling monkeys, forest-dwelling giraffes, forest-dwelling rodents, to name a few.
33:18In place of the tree-dwellers were new fossils.
33:24Fossils of completely different types of animals.
33:28Animals that lived on open plains.
33:31For some unknown reason, there had been a radiation of new forms.
33:35But what had caused it?
33:38There was a big mystery.
33:39So it was our mission, it was our task, to try to flesh out all the cause and effect here.
33:43Try to identify the causes behind this big change, this big turnover in the animals.
33:48Quaid went all over the world sampling rocks from the end of the Planet of the Apes.
33:58And everywhere he found mysterious nodules.
34:01Nodules of a substance called calcite, a carbon compound left by decaying plants.
34:06Different types of plants leave behind their own unique calcite fingerprint.
34:15Identify that fingerprint and you will know what vegetation had covered the world at the time that all these changes were happening.
34:22All that we require for a single analysis is about on that order.
34:30And that to me is an amazing thing.
34:33Because you give me a sample this size and I will reconstruct the landscape for you.
34:38The ground up nodules were mixed with acid to release carbon dioxide.
34:49The carbon dioxide was trapped in test tubes.
34:53Carbon dioxide contains radioactive isotopes which are different in every type of plant.
35:01So, identify the isotope and you identify the type of plant.
35:08Quaid's nodules showed a clear pattern.
35:12They said that 8 million years ago, much of the world was covered in forest.
35:17But by 6 million years ago, the forests had shrunk.
35:21In their place was grassland.
35:26Quaid had stumbled upon something extraordinary.
35:30He realized that he was looking at one of the great changes in life on Earth.
35:34For some unknown reason, at the end of the Planet of the Apes, there had been an environmental revolution across the planet.
35:42The perfect conditions for dramatic evolutionary change.
35:45There were clear and strong hints from paleontological records for a major extinction event.
35:53A kind of ecologic blitzkrieg in terms of the animals, that is.
35:58Really a lot of important animals that had roamed the landscape disappeared.
36:02Completely disappeared in the period of 8 to 6 million years ago.
36:05There had been a mass extinction.
36:14This explained the disappearance of the Planet of the Apes.
36:17As the forests were replaced by grassland, all sorts of forest-dwelling animals had died on a massive scale.
36:23In their place had come new species, ones that could adapt to the new world, the plane-dwellers.
36:33A vast adaptive radiation had begun.
36:36It had affected every kind of animal on the planet, except, apparently, us.
36:41Because if the theory built on Lucy was still to be believed, then her species alone had evolved without being part of this radiation.
36:54They alone came from a single elite line of creatures so special, they defied the laws of evolution.
37:01It was all starting to look a little bit absurd.
37:18No one thought the idea of our unique evolutionary path more absurd than Meve Leakey.
37:23Ever since the 1470 disaster, she'd had her suspicions about Lucy and the amazing story she seemed to tell.
37:32The news of the mass extinction and adaptive radiation prompted her to re-examine the whole issue.
37:41It's always intrigued me that we'd only knew about one species that was over 3 million years old.
37:46Because if you look at any other animal group, then you'll get radiation.
37:50And it just didn't make sense.
37:56So, last year, Meve Leakey returned to the 3 million year old rocks of northern Kenya.
38:02She was looking for a fossil.
38:09It was a fossil that, in theory, should not exist.
38:12Because most people thought that 3 and a half million years ago there was only one possible human ancestor.
38:20Only one human-like species that walked on two legs.
38:24The Australopithecine Lucy.
38:31Find a different species of human-like biped and she would have proof of adaptive radiation in humans.
38:36Proof that we had evolved just like other animals.
38:41Then one of her team spotted something.
38:44As I saw it, I stopped and bend down and look at it.
38:49I could say, what is this?
38:53So, I just said, this might be something good, but Meve was behind me about 200 meters.
39:07When we looked and it was just a few little fragments, they didn't look particularly smart, but you never know and you always hope there's going to be something more under the ground.
39:19And we were lucky.
39:21I became so happy.
39:24I didn't, I went to the camp and even I didn't do that.
39:29I didn't eat anything.
39:31I didn't eat anything.
39:32It was just the only joy that was in my heart.
39:36It was a skull, so it was, you know, really exciting.
39:40But at that point, there wasn't enough of it to say whether it was the same species as Lucy or not.
39:4525 years after they did it for the first time, Meve Leakey's team assembled a skull that they believed to be about 3 million years old.
39:59This time, there had to be no mistakes.
40:02So we spent the next year repairing all the cracks and taking all the rock off it and making it into the situation where we could start studying it.
40:11Because you can't study it obviously until it's been reconstructed and is as close as possible to its original shape.
40:24To help her, she called in Dr. Fred Spohr, an expert in anatomy from University College London.
40:31He uses a technique called computed tomography to analyse the inner structure of fossil bones.
40:38This helps him work out how a fossil fits together.
40:44The first thing they noticed was the skull had a small brain, just like Lucy.
40:50So it clearly would not resurrect the discredited big brain theory.
40:55Then came a key discovery.
40:58It was to do with how the spine entered the head.
41:01In apes, the spine always enters the head at the back of the skull.
41:07It's a typical characteristic of four-legged animals.
41:10But in the millions of years since the end of the planet of the apes,
41:15our spines have shifted to enter our head underneath the skull.
41:20This helps us to walk upright.
41:21It's one of the reasons we walk on two legs and apes don't.
41:33In the new skull, the hole for the spine was underneath, just like humans.
41:39It meant the creature must have walked on two legs.
41:44So it was a possible human ancestor.
41:47The question now was, was it just the same species as Lucy?
41:52The creature, the theory said, had evolved in one single line from apes.
41:57Or was it something different?
41:58The important question that, of course, from day one, when the specimen was found,
42:06and is always in the back of your mind, even when you're cleaning, is what is it?
42:11Ultimately, that's what we're kind of after.
42:15So, in this case, yes, we had to start comparing it with what we knew about other human ancestors
42:23from approximately the same period.
42:24And the most obvious thing was to compare it with Lucy's kind.
42:30It was then that Dr Spore made a breakthrough.
42:33It was something about the face.
42:36Apes have upper jaws that jut out, a chin that falls away,
42:41and a nose that sticks out ahead of their cheekbones.
42:44Lucy's face was like an ape's.
42:47In humans, the upper jaw, the nose, the chin, and the cheekbones are all on the same level.
42:52It means our face is flat.
42:55The new skull was also flat, like a human's.
43:00If you go from one cheekbone to the other cheekbone, you can put a pen across,
43:06and it's nearly flat, all the way here in what you call the mid-face as well.
43:12If you that now try to do here in Lucy, that's impossible, because you have that nose coming forward, so you balance over it.
43:22The difference between the new skull and Lucy was fundamental.
43:28They had to be different species.
43:31And there was more.
43:32When they dated it, they discovered the new skull was 3.5 million years old, almost exactly the same age as Lucy.
43:44It meant they had found a possible human ancestor that was of an entirely different species to Lucy, but living at exactly the same time.
43:54Lucy was not unique.
43:57Here was clear evidence of adaptive radiation in humans.
44:03And so in February this year, they announced that they had discovered flat-faced man, or as they called him, Kenyanthropus platyops.
44:15All those theories about how unique humans are, that only Lucy could have made the footprints at Lytoli, that there had only been Lucy's species, that we had followed a path of evolution different from all other animals, they have all come tumbling down.
44:41We are just like any other creature. There is nothing different or special about human evolution.
44:49We are governed by the same laws of nature as everything else.
44:54It really questions again that uniqueness.
44:58And in general, that's the theme in human evolution, to think that everything that has to do with us is unique and is different from the evolutionary patterns that you see with other animals.
45:11That just holds up less and less, and we turn out to be more and more like any other family of animals.
45:23With the announcement of Kenyanthropus this year, our family tree is now being altered.
45:28Several two-leggy creatures must have emerged from the planet of the apes. Among them, Lucy, Kenyanthropus, and who knows what else.
45:38Only one of these can be our direct ancestor. And we may never know which one.
45:44Meave Leakey thinks it could be her discovery. Kenyanthropus, the flat-faced man.
45:51For such a long time, we've believed that it was just a single lineage, a single ancestor. Now there's a choice. And we may in the future have even another choice.
46:00Because I think there's also a chance that we still haven't found the common ancestor. But there's a good chance that this could be.
46:07Could this then be the face of the earliest known human ancestor? We may never know.
46:13Because Kenyanthropus may be just one of many two-legged apes that emerged millions of years ago. And we could have evolved from any one of them.
46:24And so we can now tell a new story about our origins.
46:31It is a story, not of a creature chosen above all other animals, but of one just like any other, which evolved by chance mutation.
46:39It began, as evolution always does, with a chance event.
46:46Eight million years ago, a huge environmental upheaval began.
46:51Forests all over the world were replaced by grassland.
46:56A vast adaptive radiation began, creating a host of new species who could survive in open plains, not forests.
47:04One of these was a breed of apes that had a chance mutation.
47:11Apes that could walk on two legs.
47:14These two-legged apes would have multiplied, as did all the other new creatures, over millions of years into many related species.
47:23By the time of Lucy, three million years ago, there were perhaps half a dozen different two-legged animals of this kind.
47:31Just one of these species would have been our ancestor.
47:35For some reason, probably just sheer chance, it survived when all the other two-legged creatures died out.
47:42This animal, and we do not yet know what it was, eventually became human.
47:50One of the things we learned, looking at the fossil record like this, and looking back in time,
47:55the fact that we are here today is really very much a chance event, and we were part of the main ecosystem.
48:01We were part of the evolution that was going on with all the other animals.
48:04That is the real story of our evolution.
48:09We were not chosen.
48:11We did not defy the laws of nature.
48:14We are simply the ape that got lucky.
48:16And tomorrow morning, Horizon reveals a terrifying natural phenomenon that threatens the Turkish city of Istanbul.
48:39Earthquake storms is at the earlier time of 10.40 here on BBC Two.
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