Horizon (1964) s38e02 Episode Script

The Ape That Took Over the World

It's long been known that millions of years ago one special creature walked here.
These are fossilised footsteps from the dawn of mankind, the oldest footprints made by a human ancestor.
For years scientists have been convinced that whatever creature walked here would hold the key to the biggest mystery in all evolution: why it is that human beings have evolved to be so different, so unlike all other animals? Now a new discovery may just provide the answer to that question.
The trouble is it is not what anyone had expected.
When I first saw this fossil I realised it was going to really change our ideas of human evolution.
It is a change of such importance that the story of how man rose up from the apes and came to rule the world may now have to be rewritten.
In this secret vault in Kenya they keep human history under lock and key.
Here they guard the most precious fossils in the world, the fossils that tell the story of our evolution and there is one fossil here more remarkable that all the others found just recently.
It is of a human ancestor like no other.
We didn't realise how different it was until we began comparing in the, in the museum and that was a very exciting time because we waited such a long time to have the specimen prepared and then when we got to study it and we kept taking something else out of the cupboard and, and comparing it and it was different and this was different and that was different.
Meave Leakey and her team spent a whole year painstakingly assembling their discovery from just tiny fragments and as they analysed it further the more baffled they became.
This fossil didn't fit into any known pattern of human evolution.
We just simply couldn't find something that looked really similar.
Quite quickly we began to realise we had something very, very different and then of course it was a matter of saying well, OK, to have something different but which group does it fit in, it must fit with something that's already known and, and then it didn't, it didn't seem to work that way either and so in the end we realised that we did have something that was, it was unknown, it was new.
They had put together a skull, the oldest skull ever found of a human ancestor.
When word of this discovery spread, science was faced with something stunning because this fossil should not exist.
Because of it a mystery that many in science thought had been solved will have to be reopened, for this skull says that a key part of the theory of how human beings evolved from apes and came to dominate the planet has all been based on a mistake.
The big mystery of human evolution began ten million years ago when the Earth was a very different place, far more lush and tropical than it is today.
Back then one kind of creature reigned supreme: the apes.
They were everywhere.
The Earth really was the planet of the apes.
These were apes like we can barely imagine.
There were 50 different species of them and they roamed right across the planet.
There was the huge cevapithecus in the jungles of the East.
It 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.
This world was an ape's paradise.
For the apes living some ten 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.
Apes 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.
All this enormous variety of different types of apes disappeared about some 7 or 8 million years ago and we really cannot find an exact explication why this happened.
Seven million years later there are just a few survivors from the planet of the apes like the orang-utan, the gorilla and the chimpanzee and in place of all those apes is an animal clearly related to them, but which could not be more different: human beings.
No other creature has ever thought like us, built like us, dreamed like us.
We are more intelligent than any other animal there has ever been.
We 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.
We choose to go to the Moon in this decade and do the other things, not because they are easy but because they are hard.
Just one small step for man, one giant leap for mankind.
This 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.
In some way we had been chosen, but 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.
That was the great question the disciples of Charles Darwin, evolution's founding father, were left with.
The answer, early anthropologists thought, would lie out there in the rocks.
Somewhere there would be a fossil that could explain it all.
It would be a fossil of an animal that was basically an ape, but which showed the first key human characteristic to have evolved.
It was believed that that first key characteristic would prove to be the thing that had made us so superior to all other animals and of all the evolutionary changes between humans and apes one dwarfs them all: our brains have grown to an extraordinary size and this bewitched early anthropologists.
Humans have very large brains and our cranial capacity is about 1400 cubic centimetres and this contrasts to the chimpanzees that are around 400 cubic centimetres, so humans are three times the size of a chimpanzee brain.
And so over 100 years ago the big brain theory of human evolution was born.
It seemed obvious that our special evolutionary process must have begun with the development of our superior intelligence.
According to the theory, in the last seven million years an ape must have evolved to have a slightly bigger brain.
This more intelligent ape would have given birth to a line of progressively bigger brained super-apes who ultimately turned into humans.
When we're looking at human evolution what we have to realise is that we define ourselves by our big brain and by everything that results from that big brain and for many years palaeoanthropologists have felt that that was what we're looking for, the, the most important period in human evolution is when we see that big brain, that somehow this defines our species.
The big brain theory dominated early anthropology.
All they needed was the fossil to prove it.
It 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.
The 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? One man who thought he knew the answer was one of the anthropology's legends: Louis Leakey.
Leakey set what he called a cerebral rubicon.
By pouring beads into a skull's brain cavity and then measuring the volume of the beads it is possible to estimate brain size.
Leakey 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 centimes.
Anthropologists were trying to define what the first human would be like and they set a value for brain size that was outside the range of any known ape and they settled on a figure of about 600-700 cubic centimetres.
Leakey looked in Africa for 50 years.
He found bones of ancient apes, he even found a skull, but its brain was below the 600 cubic centimetres needed for it to be the elusive ape with the big brain, the ape that had set us out on our unique evolutionary path, but all the while he knew it had to be out there in Africa somewhere just waiting for him to find it.
By the 1970s Louis Leakey was an old man with failing health.
It was time for someone else to take up the quest.
The call was answered by Louis's son, Richard and his wife Meave.
They sent teams scouring the rocks of Kenya looking for the elusive fossil of the ape with the big brain, that key characteristic that scientists believed triggered the amazing evolution of human beings.
Then, after searching for four years, they saw something peeping out from the rocks.
It was just a few fragments sitting on the surface that really didn't look like anything and in fact the field crew had noticed it and looked at it and thought that it was bits of an antelope.
This bit of an antelope was dated at around 2.
8 million years old, halfway between the present day and the end of the planet of the apes, the perfect age for the key development that had separated humans from apes to have happened and there was something about this fossil that intrigued Richard Leakey and so he began trying to put the pieces together.
After about a week of Richard not doing a very good job, I have to say, they got bored with it and, and said OK, you have a go.
It was a task that Meave Leakey had never attempted before.
And so for the next few weeks I had a wonderful time trying to stick all these pieces together and I think it was, it was definitely one of the most challenging and exciting jigsaw puzzles I've ever done and it gradually came together.
It was not the skull of an antelope, but of an ape-like creature and it seemed to have an unusually large brain.
The question was did it cross the magical cerebral rubicon, 600 cubic centimetres? They couldn't wait to get it back to Nairobi and to do it properly, so they decided to fudge it in camp but using whatever they had and they didn't have very much, so what they did was they filled the cranium with sand and then they poured the sand into a rain gauge and they measured the amount of sand that filled the cranial vault and it came to eight inches of rain which they estimated was to be about 800cc which is pretty close.
I think now it's, it's 785 or something like that.
Richard Leakey believed he had done it.
He thought he had found the fossil his father had been looking for, so there was one person he just had to tell.
Richard said well, I really want to take it to Nairobi 'cos I want to show my father and so he flew back to Nairobi with it and to show Louis.
Louis was very excited when he, when he saw the specimen and it was, it was a great moment I think for both of them.
Two weeks later Louis Leakey died.
The skull, now known simply by its museum classification number, 14/70, seemed to have fulfilled his life's quest, to find the fossil of the ape with the big brain, the fossil that seemed to prove humans had evolved in their special way because of the early development of their intelligence.
14/70 was a sensation, reconstructed all over the world so that everyone could gaze upon this crucial human ancestor.
it became more than just a fossil, but an icon, because here seemed to be proof that what had always seemed so obvious that it must be our superior intelligence that had set us apart from all other animals and the first key evolutionary change that had begun it all must have been the development of the big brain.
So here seemed to be evidence for what you can think of as the sort of brain-led theory of human evolution, that we have a large brain early on in the course of human evolution and in a sense once you have a large brain everything else is inevitable and this seemed to show exactly that pattern.
It now seemed beyond doubt that human beings had evolved in their unique way because of the big brain, but this whole theory was about to be proved wrong.
The triumph of Leakey and 14/70 was to be short-lived.
In 1974 a young American researcher called Don Johanson was hard at it in the field looking in rocks that were about the same age as 14/70.
I was out surveying in the morning with one of my graduate students Tom Gray and as we were walking back to, to the Land Rover it was now noon time and it was, well it was close to 110 degrees and it was time to head back to camp, I happened to glance over my shoulder and as I looked down I spotted this piece of bone, a little piece of elbow, and as I looked up this slope, a very gradual slope, I saw glistening in that sunlight other pieces of bone.
They had stumbled upon almost the entire skeleton of a three million year old ape-like creature.
Here was a specimen that was astonishingly complete, something that really literally had never been found before.
Round the campfire they christened their new discovery.
One night when we were celebrating we were listening to a Beatles tape and on that tape Lucy in the Sky with Diamonds was playing and a member of the expedition said well, why don't we just call the skeleton Lucy.
Back in America they began to analyse Lucy.
She was classified as an Australopithecine, an ape-like creature, and was dated at about 3.
2 million years old, just older than 14/70, but then as they slowly put the bones together there came proof that she really was a human ancestor because this ape-like creature had one clear human characteristic and it wasn't a big brain, but something quite different.
She seemed to walk in a way that only humans do.
Lucy was, as scientists say, bipedal, unlike apes who are quadrapedal.
She walked on two legs not four.
Fortunately we had most of her pelvis preserved which of course is a critical part in terms of how an animal locomotes.
For example, a quadrapedal, a four-legged chimpanzee - this example for example - is very different from what we see in Lucy's pelvis and in, in many, many respects, not identical, but in many aspects Lucy's pelvis reminds us of our own.
Here is a, a pelvis of a modern human walking on two legs and the similarities are quite striking.
No mammals, apart from humans, have ever walked on two legs And there was more.
They found Lucy's footprints.
The fossilised Laetoli footprints were discovered in Northern Tanzania in 1976.
They are 3.
6 million years old, almost the same age as Lucy, and were just the same size as her feet.
They seemed to confirm that Australopithecines like Lucy had walked on two legs.
We're looking at the soft anatomy of, of early human ancestors who walked across a volcanic ash and left the impression of what their feet looked like.
We see that their feet were shaped just like ours, that they walked around in a manner that was almost identical to ourselves.
If Lucy had walked on two legs then it seemed she had to have been a human ancestor and that's where the trouble started because Lucy's brain was just too small.
Fortunately we had the, the, the very back portion of the skull preserved and you can tell from the curvature and the size of, of brain that would have fitted in there that it was about the size of an American softball which means about a, a third to a fourth the size of a modern human brain, so this was a creature with, with, with an ape-sized brain, very different from our own.
There was now a huge problem.
Only one of Lucy and 14/70 could be our ancestor.
Both were about three million years old, but each had different characteristics unique to humans.
If the theory was right and it really had been the development of our masterful intelligence that had led us to evolve from apes then that ancestor had to be the big brain 14/70, but now there was real doubt.
The signal that was coming out of these fossils was, was difficult to interpret because on the one hand you had 14/70 with its very large brain and on the other hand you had Lucy with a very small brain but clearly bipedal and so what, what we then had was really a period of conflict.
The only compromise, that somehow the slightly older Lucy had evolved into 14/70, was also ruled out.
14/70's brain was twice the size of Lucy's.
There was no way any creature could have doubled its brain size in the 400,000 years that separated them.
The conflict was resolved brutally.
14/70 and Lucy were dated again using radioactive dating techniques.
Both had been found between layers of volcanic rocks and volcanoes produce radioactive minerals when they erupt.
Over time these minerals decay.
By working out how far this decaying process had gone they calculated the age of the rocks in which the fossils were found.
The result would change everything.
Two-legged Lucy was just over three million years old, but big brain 14/70 was more than a million years younger, less than two million years old.
The Leakeys had blundered.
The difference was such that 14/70 could be descended from Lucy and that means the fossil of an ape-like creature with the first key human characteristic was not the big brained 14/70, but the two-legged small brained Lucy.
The big brain theory was now officially in the bin.
Instead, hard though it was to believe, it was now clear that the first key human evolutionary development that had set human beings on their unique evolutionary path was that we had walked on two legs.
They basically killed the old idea that the earliest ancestors would have a big brain because now we realised that bipedalism must have led into later ancestors with the larger brain size.
Lucy now became the great iconic fossil, the creature that held the key to why human beings were so much more intelligent than all other animals, though it was hard to see why walking on two legs had somehow made us the most intelligent beings on the planet.
Why intelligence should have evolved from moving on two legs doesn't seem obvious, so now a theory had to be devised to explain how bipedalism had let us evolve into the most amazing creature on the planet.
We suffer from back pain, fallen arches, hernias.
We're very slow, we're one of the slowest mammals around.
Think about the fact that here was a little 31ft tall Lucy walking around with lots of hungry carnivores.
She couldn't out-run a house cat, so the advantages of bipedalism must have far outweighed the disadvantages.
But then it all became clear to anthropologists.
Stage one was that by standing up our front legs became hands.
When our ancestors stood up they could begin to use their hands to carry things, to make new stones tools, to manipulate things, to use them in ways that, that quadrupeds don't.
Tools led to early technology, technology to more ways of getting food.
Better diet fed bigger brains.
This had enormous consequences for things like social organisation and language and that this was then the stimulus for the development of the larger brains.
Larger brains led to primitive culture and new ways of communicating.
Better communication led to more complex societies, more complex societies to more advanced cultures and even bigger brains and so it went on for millions of years.
So there were ways in which two legs could lead to mankind's ancestors developing bigger brains.
It seemed we had evolved into the most intelligent of all animals for one simple, crucial reason: because millions of years ago Australopithecines like Lucy walked on two legs, but there seemed to be something even more extraordinary about Lucy, something so remarkable that it confirmed what many had long believed that in some strange evolutionary way we really were unique because it began to seem that Lucy's species alone of all creatures had defied the laws of evolution.
Lucy's species should have evolved according to laws of evolution which state that major evolutionary events occur when there is a sudden and dramatic environmental change.
Those who cannot adapt to the new world die, but some animals will have a chance mutation that may help them survive in the new environment.
These survivors will form the basis of a new species.
Slowly these new species will start to exploit all the different ecological niches in the new environment.
Gradually these creatures will adapt to these different niches and slowly one new species will evolve into two.
We can see how this happens where something new arises, there's a new adaptation, a slightly better way of getting hold of food, of avoiding a predator, of walking across a landscape and that then gives that population an advantage.
It spreads out into new areas where you have one population you now have two, where you have one species you now have two species.
This is how evolutionary family trees develop.
Two species split to form separate branches.
These branches can split again and then again and so a whole host of related species will develop.
So what is happening is that each time you're getting proliferation of branches, you're getting divergence taking place and with that divergence comes what we think of as an adaptive radiation.
Adaptive radiation is one of the fundamental truths of evolution.
There are signs of it in virtually every type of animal that has ever lived, like the cat family.
The cats are a beautiful example of an adaptive radiation because you can see what they all have in common.
They have in common the fact that they are hunters and stalking hunters and they have diversified from a common ancestor into everything from lions which are very large to wild cats and lynxes that can live in cold environments to indeed domestic cats today so that they're a beautiful example of the, the shape of evolution.
Adaptive radiation has given cats a classic evolutionary family tree, lots of related species coming from lots of different branches.
It means the cat family tree has a distinctly bushy appearance and tracing any individual creature's line of ancestors is a complex business.
If Lucy's species had evolved like any other animal her evolutionary tree should have the same bushy shape.
There should be lots of two-legged creatures appearing just after the planet of the apes, but the fossil record seemed to show that the only signs of adaptive radiation came well after Lucy.
All the fossils leading back from Lucy to the planet of the apes seemed to be just primitive versions of the same Australopithecine Lucy.
It seemed that Lucy had evolved without any adaptive radiation.
Our family tree appeared to have no related branches before Lucy at all but was just a solitary straight line and this defied the laws of evolution.
One would expect to look at human evolution as an adaptive radiation, but the way it was always reconstructed was very much as a linear story and I think that actually goes back to the idea of human uniqueness.
People expected humans to evolve differently and uniquely and have a single line.
It seemed to many that the old idea that humans were different from all other animals was right.
Every other creature had followed the typical evolutionary pattern of adaptive radiation, except Lucy's species.
She alone seemed to have emerged from a single elite line of super-creatures so special they defied the laws of evolution.
Then, thousands of miles from Africa, a chain of events began that would alter our whole attitude to Lucy and her species' extraordinary ability to defy the laws of evolution.
Along came Jay Quade.
He couldn't care less about human evolution.
He's a geochemist, an expert in the chemical composition of rocks.
A few years ago he was contacted by some baffled palaeontologists.
They had noticed something strange about fossils dating from between 6-8 million years ago, fossils from the end of the planet of the apes.
A whole swathe of animals, not just the apes, seemed to disappear and they all had one thing in common: they lived in the same environment.
Starting about eight million years ago what was disappearing were animals that they believed were specific to a forested habitat: tree dwelling orang-utans, tree dwelling monkeys, forest dwelling giraffes, forest dwelling rodents to name a few.
In place of the tree dwellers were new fossils, fossils of completely different types of animals, animals that lived on open plains.
For some unknown reason there had been a radiation of new forms, but what had caused it? There was a big mystery and so it was our mission, it was our task to try and flesh out all the cause and effect here, try to identify the causes behind this big change, this big turnover in, in the animals.
Quade went all over the world sampling rocks from the end of the planet of the apes and everywhere he found mysterious nodules, nodules of a substance called calcite, a carbon compound left by decaying plants.
Different types of plants leave behind their own unique calcite fingerprint.
Identify that fingerprint and you will know what vegetation have covered the world at the time that all these changes were happening.
All that we require for a single analysis is it's about on, on that order and that to me is an amazing thing because you can give me a sample this size and I'll reconstruct a landscape for you.
The ground up nodules were mixed with acid to release carbon dioxide.
The carbon dioxide was trapped in test tubes.
Carbon dioxide contains radioactive isotopes which are different in every type of plant.
So identify the isotope and you identify the type of plant.
Quade's nodules showed a clear pattern.
They said that eight million years ago much of the world was covered in forest, but by six million years ago the forests had shrunk.
In their place was grassland.
Quade had stumbled upon something extraordinary.
He realised that he was looking at one of the great changes in life on Earth.
For some unknown reason at the end of the planet of the apes there had been an environmental revolution across the planet, the perfect conditions for dramatic evolutionary change.
There were clear and strong hints from paleontological records for a major extinction event, a kind of ecologic blitzkrieg in terms of the animals that is, that really a lot of, lot of important animals that had roamed the landscape disappeared, completely disappeared in the period 8-6 million years ago.
There had been a mass extinction.
This explained the disappearance of the planet of the apes.
As the forests were replaced by grassland all sorts of forest dwelling animals had died on a massive scale.
In their place had come new species, ones that could adapt to the new world, the plain dwellers.
A vast adaptive radiation had begun.
It had affected every kind of animal on the planet, except apparently us, because if the theory built on Lucy was still to be believed then her species alone had evolved without being part of this radiation.
They alone came from a single elite line of creatures so special they defied the laws of evolution.
It was all starting to look a little bit absurd.
No one thought the idea of our unique evolutionary path more absurd than Meave Leakey.
Ever since the 14/70 disaster she had her suspicions about Lucy and the amazing story she seemed to tell.
The news of the mass extinction and adaptive radiation prompted her to re-examine the whole issue.
It's always intrigued me that we only knew about one species that was over three million years old because if you look at any other animal group then you'll get radiation and it just didn't make sense.
So last year Meave Leakey returned to the three million year old rocks of Northern Kenya.
She was looking for a fossil.
It was a fossil that, in theory, should not exist because most people thought that 31 million years ago there was only one possible human ancestor, only one human-like species that walked on two legs, the Australopithecine Lucy.
Find a different species of human-like biped and she would have proof of adaptive radiation in humans, proof that we had evolved just like other animals.
Then one of her team spotted something.
As I saw it I stopped and bended down and look at it, I couldn't say what is this? So I just it's this might be something good but it was behind me about 200 metres.
When we looked and it was just a few little fragments.
It didn't look particularly smart, but you never know and you always hope there's going to be something more under the ground and we were lucky.
I became so happy.
I went to the camp I didn't eat anything, so it was just only joy that was in my heart.
It was a skull so it was, you know, really exciting but at that point there wasn't enough of it to say whether it was the same species as Lucy or not.
25 years after they did it for the first time, Meave Leakey's team assembled a skull that they believed to be about three million years old.
This time there had to be no mistakes.
So 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 study, studying it 'cos you can't study it obviously until, until it's been reconstructed and is as close as possible to its original shape.
To help her she called in Dr Fred Spoor, an expert in anatomy from University College, London.
He uses a technique called computer tomography to analyse the inner structure of fossil bones.
This helps him work out how a fossil fits together.
The first thing they noticed was the skull had a small brain, just like Lucy, so it clearly would not resurrect the discredited big brain theory.
Then came a key discovery.
It was to do with how the spine entered the head.
In apes the spine always enters the head at the back of the skull.
It's a typical characteristic of four-legged animals, but in the millions of years since the end of the planet of the apes our spines have shifted to enter our head underneath the skull.
This helps us to walk upright.
It's one of the reasons we walk on two legs and apes don't.
In the new skull the hole for the spine was underneath, just like humans.
It meant the creature must have walked on two legs, so it was a possible human ancestor.
The question now was: was it just the same species as Lucy, the creature, the theory said, had evolved in one single line from apes, or was it something different? The important question that of course from day one when the, when the specimen was found and is always in the back of your mind even when you're cleaning is: what is it? Ultimately that's what we're kind of after.
So in this case yes, we had to start comparing it with what we knew about other human ancestors from approximately the same period and, and the most obvious thing was to compare it with Lucy's kind.
It was then that Dr Spoor made a breakthrough.
It was something about the face.
Apes have upper jaws that jut out, a chin that falls away and a nose that sticks out ahead of their cheekbones.
Lucy's face was like an ape's.
In humans the upper jaw, the nose, the chin and the cheekbones are all on the same level.
It means our face is flat.
The new skull was also flat like a human's.
If you go from one cheekbone to the other cheekbone you can put a pen across and it's nearly, nearly flat, all the way here in what you call the mid-face as well.
If you now try to do here in, in Lucy that's impossible because you have that nose coming forward so you, you, you balance over it.
The difference between the new skull and Lucy was fundamental.
They had to be different species and there was more.
When they dated it they discovered the new skull was 31 million years old, almost exactly the same age as Lucy.
It meant they had found a possible human ancestor that was of an entirely different species to Lucy, but living at exactly the same time.
Lucy was not unique.
Here was clear evidence of adaptive radiation in humans and so in February this year they announced that they had discovered flat face man, or as they called him Kenyanthropus platyops.
All those theories about how unique humans are, that only Lucy could have made the footprints at Laetoli, that there had only been Lucy's species, that we have followed a path of evolution different from all other animals, they have all come tumbling down.
We are just like any other creature.
There is nothing different or special about human evolution.
We are governed by the same laws of nature as everything else.
It really questions again that, that uniqueness and in general that's, that's the theme in human evolution to think that everything that has to do with us is, is unique and is different from the evolutionary patterns that you see with other animals.
That just holds up less and less and we turn out to be more and more like any other family of, of animals.
With the announcement of Kenyanthropus this year our family tree is now being altered.
Several two-legged creatures must have emerged from the planet of the apes.
Among them Lucy, Kenyanthropus and who knows what else.
Only one of these can be our direct ancestor and we may never know which one.
Meave Leakey thinks it could be her discovery, Kenyanthropus, the flat face man.
For such a long time we've believed there was just a single linear, a single ancestor.
Now there's a choice and we may in the future have even another choice because I think there's another, there's also a chance that we still haven't found the common ancestor, but there's a good chance that this could be it.
Could this then be the face of the earliest known human ancestor? We may never know because 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 and so we can now tell a new story about our origins.
It is a story not of a creature chosen above all other animals, but of one just like any other which evolved by chance mutation.
it began, as evolution always does, with a chance event.
Eight million years ago a huge environmental upheaval began.
Forests all over the world were replaced by grassland.
A vast adaptive radiation began creating a host of new species who could survive in open plains not forests.
One of these was a breed of apes that had a chance mutation, apes that could walk on two legs.
These two-legged apes would have multiplied, as did all the other new creatures over millions of years into many related species.
By the time of Lucy, three million years ago, there were perhaps half a dozen different two-legged animals of this kind.
Just one of these species would have been our ancestor.
For some reason, probably just sheer chance, it survived when all the other two-legged creatures died out.
This animal, and we do not yet know what it was, eventually became human.
One of the things we learnt looking at the fossil record like this and, and looking back in time, the fact that we're here today is really very much a chance event and we were part of, of a main ecosystem, we were part of the evolution that was going on with, with all the other animals.
That is the real story of our evolution.
We were not chosen, we did not defy the laws of nature, we are simply the ape that got lucky.