0:00:06 > 0:00:09The shape of your face...
0:00:09 > 0:00:12Walking on two legs...
0:00:12 > 0:00:15The way you see the world...
0:00:15 > 0:00:18What makes you the person you are?
0:00:22 > 0:00:26The story of each and every one of us
0:00:26 > 0:00:31can be traced back millions of years to the plains of ancient Africa.
0:00:33 > 0:00:36The answers to the question, "What makes us human?"
0:00:36 > 0:00:41lie buried in the ground in the fossils and other traces of our ancestors,
0:00:41 > 0:00:48but also lie deep within our own bodies, in our bones, flesh and genes.
0:00:51 > 0:00:55As an anatomist, I'm fascinated by the way our bodies
0:00:55 > 0:00:56have been sculpted
0:00:56 > 0:01:00by our ancestors' struggle for survival.
0:01:06 > 0:01:09But why did we leave behind the other apes in the forest...
0:01:12 > 0:01:16..and stride out into the African savannah?
0:01:18 > 0:01:22How did that change the way we looked...
0:01:23 > 0:01:27..give us big muscles in the unlikeliest of places...
0:01:29 > 0:01:33..and help us to acquire amazing new skills?
0:01:35 > 0:01:43The story of how we became human describes how forest-dwelling apes evolved into us
0:01:43 > 0:01:46and the story starts millions of years ago,
0:01:46 > 0:01:50with an ape who stood upright and walked.
0:02:27 > 0:02:31Our story began around six million years ago,
0:02:31 > 0:02:35with apes who lived in an ancient African forest.
0:02:36 > 0:02:39In many ways, they would have been similar to the apes
0:02:39 > 0:02:42that still live in the forests here today.
0:02:47 > 0:02:50I'm here in the ancient forest of Kibale in Uganda,
0:02:50 > 0:02:53which covers about 700 square kilometres,
0:02:53 > 0:02:56and I'm hoping to do something really special,
0:02:56 > 0:03:01and that's to track down some of our closest living relatives - chimpanzees.
0:03:08 > 0:03:15I want to get close enough to see how their bodies work,
0:03:15 > 0:03:20but getting near to the wild chimps who live in this dense, wet forest isn't easy.
0:03:23 > 0:03:26'Francis Mugurusi is my guide.'
0:03:26 > 0:03:28Hello, where are the chimpanzees?
0:03:28 > 0:03:33'He's been studying the chimps here for nearly 20 years.'
0:03:38 > 0:03:40I think we're getting close now.
0:03:40 > 0:03:44Francis, my guide, tells me that he can hear the chimpanzees.
0:03:44 > 0:03:47He thinks there's two groups, one further away over there,
0:03:47 > 0:03:51but also a group which is much nearer, perhaps only five or ten minutes away.
0:03:51 > 0:03:54So this is really exciting.
0:03:55 > 0:04:00CHIMPS SQUEAL IN THE DISTANCE
0:04:10 > 0:04:11CHIMP CALLS
0:04:11 > 0:04:16SEVERAL CHIMPS CALLING
0:04:33 > 0:04:36Oh, there's lots of them, they're all around us.
0:04:45 > 0:04:48This is just extraordinary.
0:04:48 > 0:04:51This is my first sight of chimpanzees in the wild.
0:05:04 > 0:05:08It's impossible to look at chimpanzees and think that we're not related to them.
0:05:08 > 0:05:11Of course, they are our closest living relatives.
0:05:11 > 0:05:13I mean, look at the way he's sitting there.
0:05:18 > 0:05:22We are so closely related to chimpanzees,
0:05:22 > 0:05:25we share nearly 99% of our DNA with them.
0:05:26 > 0:05:28BREAKING WIND
0:05:28 > 0:05:31I just want to say, that's not me.
0:05:32 > 0:05:35But although we're genetically close,
0:05:35 > 0:05:38we are not descended from them.
0:05:48 > 0:05:51Looking at chimpanzees helps us understand where we've come from
0:05:51 > 0:05:55and that's not because we've evolved from them, of course we haven't,
0:05:55 > 0:05:59but if we trace back each of our family trees far enough
0:05:59 > 0:06:01we reach a point where they come together.
0:06:01 > 0:06:05We have a common ancestor with chimpanzees,
0:06:05 > 0:06:08going back about six or seven million years ago.
0:06:08 > 0:06:11So I'm here visiting my relatives.
0:06:11 > 0:06:16Now, their ancestors stayed in the forests, whereas ours moved out.
0:06:16 > 0:06:20And if we can find out how and why we did that,
0:06:20 > 0:06:24well, that's the story of how we became human.
0:06:27 > 0:06:32Our evolutionary journey is written into our bodies
0:06:32 > 0:06:36and into the way we use them.
0:06:36 > 0:06:42And a chimpanzee's body is built for a particular way of getting around.
0:06:49 > 0:06:51(He's fast asleep.)
0:06:56 > 0:07:00Literally, just a few metres away.
0:07:07 > 0:07:11He's just having a quick look around, but basically he's dozing,
0:07:11 > 0:07:14lying on his back with his limbs splayed out.
0:07:14 > 0:07:17He's got these wonderfully long arms
0:07:17 > 0:07:20and very short legs - he's a climber.
0:07:22 > 0:07:23And his feet are wonderful.
0:07:23 > 0:07:27He's still got this grasping ability in his feet that we've lost.
0:07:27 > 0:07:30He's able to grip onto things and climb.
0:07:30 > 0:07:33His great toe, his big toe, is out to the side like that,
0:07:33 > 0:07:36so it makes his feet look like hands.
0:07:37 > 0:07:39'Millions of years ago,
0:07:39 > 0:07:44'our ancestors would have had feet which grasped like this.'
0:07:44 > 0:07:47And that's something that we've lost.
0:08:01 > 0:08:06'In six million years, our body plan has become very different,
0:08:06 > 0:08:10'with our long legs and feet for walking on.'
0:08:16 > 0:08:17SHE PANTS
0:08:17 > 0:08:22It look as though they've moving quite slowly, but I can assure you they're not.
0:08:22 > 0:08:25This is a fairly fast pace to be moving through the jungle.
0:08:28 > 0:08:33'So what was it that set our ancestors off on a different path,
0:08:33 > 0:08:37'a path that would lead us to colonise the globe,
0:08:37 > 0:08:40'whilst other apes stayed in the African forest?
0:08:40 > 0:08:43'And when did we start to change?'
0:08:47 > 0:08:49It's always been a puzzle.
0:08:50 > 0:08:55Until this extraordinary fossil was discovered just a few years ago.
0:08:58 > 0:09:04This is Toumai, also known as sahelanthropus tchadensis,
0:09:04 > 0:09:09and it's not putting it too strongly to say that his discovery caused something of a stir.
0:09:09 > 0:09:13He certainly looks like an ape, and just to convince you of that,
0:09:13 > 0:09:16I've got a modern chimpanzee skull
0:09:16 > 0:09:19and you can see how similar the two are.
0:09:19 > 0:09:21They've even got a similar sized brain.
0:09:21 > 0:09:25But there's something very special about Toumai.
0:09:25 > 0:09:28And just to explain that, first of all I want to show you
0:09:28 > 0:09:31the foramen magnum underneath the chimpanzee skull.
0:09:31 > 0:09:34This is where the spinal cord exits the skull.
0:09:34 > 0:09:39If I hold the chimpanzee skull in that orientation,
0:09:39 > 0:09:41as the skull would be in life,
0:09:41 > 0:09:44with the eye sockets in a vertical plane,
0:09:44 > 0:09:49we can see that the foramen magnum exits the skull at this angle.
0:09:49 > 0:09:52In Toumai it's completely different.
0:09:52 > 0:09:55The foramen magnum is right underneath the skull,
0:09:55 > 0:10:00which means the skull is balancing on an erect spine.
0:10:00 > 0:10:01This isn't any old ape.
0:10:01 > 0:10:06This is an ape who stood upright on two legs.
0:10:06 > 0:10:10And not only that, this is a bipedal ape,
0:10:10 > 0:10:13who dates to six to seven million years ago.
0:10:16 > 0:10:20This is a hugely significant moment in our story.
0:10:25 > 0:10:28It means that Toumai was moving around on two legs,
0:10:28 > 0:10:33very close to the time our ancestors split from chimpanzees.
0:10:33 > 0:10:38There's no question he's more chimpanzee-like than human
0:10:38 > 0:10:43but Toumai puts standing up right at the start of our journey.
0:10:55 > 0:10:59In the six million years since Toumai stood upright,
0:10:59 > 0:11:03our skeleton has undergone many changes.
0:11:05 > 0:11:09Our bones and muscles have been transformed
0:11:09 > 0:11:15by this new way of getting around, upright, on two legs.
0:11:20 > 0:11:24I'm a human anatomist - I've studied the structure of the human body
0:11:24 > 0:11:26and I've mainly done that through dissection.
0:11:26 > 0:11:29And in fact, that's exactly what anatomy means,
0:11:29 > 0:11:32it means to take apart.
0:11:32 > 0:11:35But today I'm trying out something a bit different.
0:11:35 > 0:11:40I'm putting the human body, or at least the skeleton, back together again.
0:11:46 > 0:11:49This skeleton is, as you might expect, white,
0:11:49 > 0:11:52but in fact that's because these are dead bones.
0:11:52 > 0:11:55Living bones are pink because they're full of blood.
0:11:55 > 0:11:58Anybody that's broken a bone will know that.
0:11:58 > 0:12:00A fractured bone bleeds like crazy.
0:12:02 > 0:12:05Living bone in our bodies constantly changes
0:12:05 > 0:12:10in response to the stresses and the strains we place it under.
0:12:10 > 0:12:14So, over a period of years, all of the bone in your skeleton
0:12:14 > 0:12:17is taken away and replaced with new bone.
0:12:20 > 0:12:22But standing up on two legs
0:12:22 > 0:12:27is dependent on a central yet vulnerable part of our anatomy.
0:12:27 > 0:12:31Right in the centre of the skeleton is this wonderful structure,
0:12:31 > 0:12:35the spine, built up of a series of repeating vertebrae,
0:12:35 > 0:12:39and it forms this beautiful double-S shape.
0:12:42 > 0:12:46But all of this anatomical beauty comes at a cost.
0:12:48 > 0:12:52With this isolated spine, you can see the curves beautifully,
0:12:52 > 0:12:54but you can see something else,
0:12:54 > 0:12:58and that's the increase in size of the vertebrae as we go down,
0:12:58 > 0:13:01until we get to here, the lumbar spine,
0:13:01 > 0:13:04where the vertebrae are absolutely massive.
0:13:04 > 0:13:08And that's because they're bearing the weight of everything above them.
0:13:08 > 0:13:10So it's not surprising
0:13:10 > 0:13:14that this is where we tend to get problems with our spines,
0:13:14 > 0:13:17and, in fact, it's the most common reason for visits to GPs.
0:13:17 > 0:13:21As we get older, the intervertebral discs start to dry out,
0:13:21 > 0:13:25and the inside of them can pop out and press on the spinal nerves,
0:13:25 > 0:13:26and that can be painful.
0:13:26 > 0:13:30And also the weight that is borne by the spine moves backwards
0:13:30 > 0:13:33and now is loaded onto these joints at the back,
0:13:33 > 0:13:36so they can be painful, too.
0:13:36 > 0:13:42So if standing upright causes us so many problems, why did we do it?
0:13:49 > 0:13:55The answer is locked away in the dark recesses of time.
0:13:58 > 0:14:00Six million years ago,
0:14:00 > 0:14:03the world's climate was becoming colder and drier,
0:14:03 > 0:14:08and the forests of Africa were thinning out.
0:14:09 > 0:14:13And where dense jungles gave way to woodlands,
0:14:13 > 0:14:16the apes who lived in them started to change.
0:14:21 > 0:14:25BARKING AND CHATTER OF CHIMPANZEES
0:14:27 > 0:14:32You can see what might have happened by looking at apes living today.
0:14:39 > 0:14:41'Up in the trees,
0:14:41 > 0:14:46'some of the best food is in the most inaccessible places.
0:14:48 > 0:14:53'And being able to reach the highest branches is an obvious advantage.'
0:14:56 > 0:15:01They are feeding on a fruit.
0:15:01 > 0:15:03It's one of their favourite fruits that they feed on.
0:15:03 > 0:15:04So they're eating fruits up there?
0:15:04 > 0:15:08Yes, they're eating ripe fruits, and there are some that have fallen
0:15:08 > 0:15:12with the leaves and branch here.
0:15:12 > 0:15:15- Oh, right, yeah. Can I taste it? - Yes, we can taste.
0:15:15 > 0:15:19- So the little yellow ones are ripe? - Yes, they are ripe, and they like it.
0:15:21 > 0:15:23Mmm.
0:15:23 > 0:15:25- It's somehow bitter.- It is bitter.
0:15:25 > 0:15:26But for them, they like it.
0:15:26 > 0:15:30- It's not one of my favourite fruits. - It can't be your favourite.
0:15:34 > 0:15:39CHIMPANZEES HOOT AND SCREECH
0:15:39 > 0:15:42In an increasingly patchy woodland,
0:15:42 > 0:15:45being able to stand to reach fruit on the thinnest branches
0:15:45 > 0:15:50must have been a great advantage for our ancestors.
0:15:52 > 0:15:58And it's possible that this is what drove the changes in Toumai's body.
0:15:58 > 0:16:03He could have been standing upright in the trees.
0:16:09 > 0:16:11The latest discoveries
0:16:11 > 0:16:15show that Toumai was the first of many bipedal apes.
0:16:17 > 0:16:19Over the next two million years,
0:16:19 > 0:16:25fossils like Orrorin tugenensis and Ardipithecus ramidus
0:16:25 > 0:16:28show that other apes were also adapting
0:16:28 > 0:16:32to their changing environment by standing upright.
0:16:32 > 0:16:36They were still essentially climbers but as the forests thinned,
0:16:36 > 0:16:40it's thought these apes were spending more time on the ground.
0:16:47 > 0:16:49It's hard to know exactly when
0:16:49 > 0:16:55our ancestors gave up a life in the trees for living on the ground.
0:16:58 > 0:17:02But there is a clue, hidden away in our bones.
0:17:05 > 0:17:08I've been watching the chimpanzees climbing,
0:17:08 > 0:17:10and the way their ankles work,
0:17:10 > 0:17:12so I want to compare that with my ankle.
0:17:12 > 0:17:15Sorry about this, but the boot and the sock are coming off.
0:17:15 > 0:17:18Now most of the time I'm walking around on the ground,
0:17:18 > 0:17:22and my foot is at 90 degrees to my leg.
0:17:22 > 0:17:25But I can move the ankle like this,
0:17:25 > 0:17:28that's called dorsiflexion,
0:17:28 > 0:17:31to about 20 degrees.
0:17:31 > 0:17:34Now compare that with chimpanzees.
0:17:36 > 0:17:40To climb efficiently on something vertical,
0:17:40 > 0:17:44you need to be able to bend your foot up much more than we can.
0:17:44 > 0:17:46When chimps are climbing,
0:17:46 > 0:17:50they dorsiflex their ankles up to 45 degrees.
0:17:51 > 0:17:55The differences in ankle movement between us and them
0:17:55 > 0:17:58could provide vital evidence in working out
0:17:58 > 0:18:02exactly when our ancestors gave up climbing for walking.
0:18:21 > 0:18:26To nail down when we became walking rather than climbing apes,
0:18:26 > 0:18:29scientists at Boston University have been studying the bones
0:18:29 > 0:18:32of our ancient ancestors with laser-like precision.
0:18:38 > 0:18:40They've analysed the remains of every fossil
0:18:40 > 0:18:43they could lay their hands on...
0:18:44 > 0:18:51..including the bones of this truly remarkable fossil - Lucy.
0:18:53 > 0:18:59She belongs to a species called Australopithecus afarensis.
0:18:59 > 0:19:03This is a replica of Lucy, who is one of the most famous,
0:19:03 > 0:19:07if not THE most famous skeletons in the whole of human evolution.
0:19:07 > 0:19:13She's 3.2 million years old, and we have so much of her skeleton
0:19:13 > 0:19:17that we can tell an enormous amount about her.
0:19:17 > 0:19:19She would have stood just over a metre tall.
0:19:19 > 0:19:22The length of her arms and her curved fingers
0:19:22 > 0:19:27suggest that climbing was still really important
0:19:27 > 0:19:29in the way she got around.
0:19:29 > 0:19:33But recent research is challenging that idea.
0:19:37 > 0:19:39There's one area of Lucy's skeleton
0:19:39 > 0:19:44that's been the focus of Jeremy DeSilva's exciting new research.
0:19:44 > 0:19:48Lucy has a spectacular ankle, uh... and we have some comparisons.
0:19:48 > 0:19:50Great, so this is a chimp.
0:19:50 > 0:19:54Right, and this is a human, and chimpanzees,
0:19:54 > 0:19:57they do remarkable things with their feet and ankles.
0:19:57 > 0:19:59They could take the top of their foot
0:19:59 > 0:20:01and press it right up against their shin.
0:20:01 > 0:20:06It's amazing flexion, which if you and I tried that,
0:20:06 > 0:20:10we'd snap ligaments and our Achilles, we just aren't equipped for that.
0:20:10 > 0:20:12A big ape like a chimpanzee,
0:20:12 > 0:20:15putting all of its body on the foot and on the ankle
0:20:15 > 0:20:18while it's climbing like that, leaves its mark on the bones.
0:20:20 > 0:20:23On the left is the bottom of a chimpanzee's tibia,
0:20:23 > 0:20:26or shin bone, where it forms the ankle joint,
0:20:26 > 0:20:30and there's a very obvious trapezoid shape.
0:20:30 > 0:20:33On the right is the same area of the human tibia,
0:20:33 > 0:20:37and it's square.
0:20:37 > 0:20:39The shape of your bones reflects
0:20:39 > 0:20:42whether you use your ankles for climbing or for walking.
0:20:45 > 0:20:50OK, so...let's have a look at Lucy and compare her.
0:20:50 > 0:20:53Well, although she's tiny,
0:20:53 > 0:20:56the shape of that joint just there
0:20:56 > 0:20:59- is much more human-like.- It is.
0:20:59 > 0:21:02And that tells us that her feet were planted firmly on the ground
0:21:02 > 0:21:04directly underneath her knees,
0:21:04 > 0:21:07the adaptations we see in upright-walking creatures.
0:21:07 > 0:21:09- Fantastic.- Like us.
0:21:09 > 0:21:13- Amazing to be able to tell so much just from the end of one bone.- Yes.
0:21:13 > 0:21:17And the magnificent thing about Lucy is that we have so many bones,
0:21:17 > 0:21:21and each one of those bones tells a fascinating story.
0:21:26 > 0:21:29Lucy still appears very ape-like,
0:21:29 > 0:21:33and her brain was similar in size to that of a chimpanzee's.
0:21:36 > 0:21:40But becoming a walking ape
0:21:40 > 0:21:43had fundamentally changed the shape of her body.
0:21:48 > 0:21:51By the time we see Australopithecines like Lucy,
0:21:51 > 0:21:55we can be absolutely sure beyond a shadow of a doubt,
0:21:55 > 0:22:00that our ancestors were standing and walking around on two legs.
0:22:00 > 0:22:04And not only that, they were committed to walking.
0:22:04 > 0:22:07It was their main way of getting around.
0:22:10 > 0:22:16'Giving up climbing for walking suggests that our ancestors
0:22:16 > 0:22:20'were moving beyond the confines of the forest,
0:22:20 > 0:22:24'that they were exploring new habitats.
0:22:26 > 0:22:31'But walking is a physical skill that takes time to learn.
0:22:39 > 0:22:43'Just think about what these babies are trying to do.
0:22:48 > 0:22:53'Balancing on their tiny little feet, defying gravity.
0:23:04 > 0:23:08'Some of us get the hang of it quicker than others.
0:23:14 > 0:23:18'And some of us aren't in a rush to do anything.
0:23:21 > 0:23:27'But most of us will, at some stage in our early childhood,
0:23:27 > 0:23:28'stagger to our feet and walk.'
0:23:31 > 0:23:33These little ones are just learning
0:23:33 > 0:23:36to do something that's incredibly difficult.
0:23:36 > 0:23:40They've been quite happy for a few months crawling around on all fours,
0:23:40 > 0:23:46but now they really want to get up onto two feet and start walking.
0:23:46 > 0:23:49And at any point in time, when she cracks it,
0:23:49 > 0:23:52she'll be balancing on just one foot.
0:23:55 > 0:24:00'And with each step, this involves coordinating some 200 muscles.
0:24:04 > 0:24:12'It's an amazing feat of learning, but there are physical changes too.
0:24:19 > 0:24:23'As these toddlers learn to walk, their bodies are changing.'
0:24:23 > 0:24:25They're using their muscles in different ways,
0:24:25 > 0:24:28and the muscles will develop accordingly.
0:24:28 > 0:24:31And deep inside their bodies, their bones are changing as well.
0:24:31 > 0:24:35They'll start to develop the backwards curve in the lower spine
0:24:35 > 0:24:39and the bottom of the spine will push down between the two hip bones.
0:24:39 > 0:24:41The hip bones curve forwards,
0:24:41 > 0:24:45and the thigh bone also starts to curve forwards and bend inwards.
0:24:45 > 0:24:49But what's really interesting is that we don't know
0:24:49 > 0:24:52how much these changes are programmed,
0:24:52 > 0:24:54and how much they're appearing,
0:24:54 > 0:24:58they're developing, in response to walking.
0:24:58 > 0:24:59- Ooh!- And jumping.
0:25:06 > 0:25:09'It's obvious that the evolution of walking
0:25:09 > 0:25:12'has had a profound impact on our bodies.
0:25:15 > 0:25:19'And it all started with those ancestors who put one foot
0:25:19 > 0:25:21'in front of the other.'
0:25:37 > 0:25:42It took millions of years for our ancestors
0:25:42 > 0:25:45to master the art of standing and then walking.
0:25:55 > 0:25:58But walking would fundamentally alter the course
0:25:58 > 0:26:00of our evolutionary history.
0:26:11 > 0:26:16And the next critical step on the long road to becoming human
0:26:16 > 0:26:21was driven by a new wave of drastic climate change.
0:26:23 > 0:26:28From around three million years ago, East Africa started to dry
0:26:28 > 0:26:30and the forests shrank back.
0:26:31 > 0:26:35A brand-new habitat was born - the savannah.
0:26:40 > 0:26:44This was a whole new world, rich with opportunity,
0:26:44 > 0:26:47and evolution went into overdrive.
0:26:48 > 0:26:51There was an explosion of species taking advantage
0:26:51 > 0:26:54of the expanding grasslands.
0:27:02 > 0:27:06And alongside them were new species of walking apes,
0:27:06 > 0:27:10who strode out on two legs into the changing landscape...
0:27:11 > 0:27:14forming new branches of our family tree.
0:27:21 > 0:27:24Giving up climbing for walking
0:27:24 > 0:27:26meant that this group of apes
0:27:26 > 0:27:29were in the right place at the right time.
0:27:32 > 0:27:36As the forests receded, the walking ape came into its own.
0:27:36 > 0:27:40In fact, we know from the fossils that around two million years ago
0:27:40 > 0:27:43there were at least six different species
0:27:43 > 0:27:47of these hominines, these apes which habitually walked on two legs.
0:27:47 > 0:27:51It was a big, bushy family tree.
0:27:51 > 0:27:55But while most of those lineages would eventually die out,
0:27:55 > 0:27:58one would go on to be extraordinarily successful.
0:28:06 > 0:28:10We don't really know why any of the others died out,
0:28:10 > 0:28:14but the thought that any of our ancestors could have survived
0:28:14 > 0:28:18in this arid, open environment is difficult to comprehend.
0:28:20 > 0:28:22For a relatively puny forest ape,
0:28:22 > 0:28:27life on the savannah would surely have been a dangerous proposition.
0:28:29 > 0:28:31I am feeling quite nervous
0:28:31 > 0:28:35and extremely vulnerable, out here on the plain.
0:28:35 > 0:28:38I'm keeping my eyes peeled
0:28:38 > 0:28:42and I can see some gazelles over there, and some zebra,
0:28:42 > 0:28:47but I know that there are much more dangerous animals here as well.
0:28:47 > 0:28:49I saw some lions earlier, and a cheetah.
0:28:51 > 0:28:55And there would have been similarly formidable predators here
0:28:55 > 0:28:57two million years ago.
0:28:57 > 0:29:01So, how did our ancestors survive on the open savannah?
0:29:17 > 0:29:20This extraordinary fossil skeleton of a young male,
0:29:20 > 0:29:21unearthed here in Kenya,
0:29:21 > 0:29:25gives us an insight into how our ancestors
0:29:25 > 0:29:30managed not only to survive but to thrive on the savannah.
0:29:32 > 0:29:35I've really enjoyed laying this skeleton out.
0:29:35 > 0:29:36I've seen so many pictures of it
0:29:36 > 0:29:40but there's nothing quite like being able to handle the real thing.
0:29:40 > 0:29:42Well, actually, this is a replica,
0:29:42 > 0:29:47but it is one of THE most famous early human fossils.
0:29:47 > 0:29:52And it's just remarkable how much of the skeleton has been preserved,
0:29:52 > 0:29:54how many bones we have here.
0:29:54 > 0:29:58It dates back to one-and-a-half-million years ago.
0:29:58 > 0:30:03He's called KNM-WT 15000,
0:30:03 > 0:30:06or, perhaps more poetically, Nariokotome Boy.
0:30:06 > 0:30:11And his bones tell us something really important
0:30:11 > 0:30:16about a crucial change to our bodies in human evolution.
0:30:21 > 0:30:24There are clues all over his skeleton,
0:30:24 > 0:30:28but the most striking are in the lower half of his body.
0:30:28 > 0:30:33Just look at the length of these legs. It is stunning.
0:30:34 > 0:30:38If I put my leg down beside Nariokotome Boy's leg,
0:30:38 > 0:30:41you can see that it's practically the same length.
0:30:41 > 0:30:45His femur fits along my thigh,
0:30:45 > 0:30:48his tibia...
0:30:49 > 0:30:53fits quite nicely along my lower leg there.
0:30:53 > 0:30:57And these long legs really are
0:30:57 > 0:31:00an important step forward in human evolution.
0:31:00 > 0:31:03This is the first time we've seen somebody who looks human -
0:31:03 > 0:31:06he could be walking out there, in this landscape,
0:31:06 > 0:31:11and you would not notice that he wasn't one of us.
0:31:15 > 0:31:17Nariokotome Boy was a member
0:31:17 > 0:31:20of a species of early humans known as Homo erectus.
0:31:24 > 0:31:28He may be nearly two million years old,
0:31:28 > 0:31:31but his body plan was obviously highly effective,
0:31:31 > 0:31:35because from the neck down, he's so similar to us today.
0:31:37 > 0:31:41But his brain was only two-thirds the size of ours.
0:31:41 > 0:31:44He didn't get by on his wits alone.
0:31:48 > 0:31:52So is there anything else about him that can tell us
0:31:52 > 0:31:54how he survived out here?
0:31:54 > 0:31:58There are plenty of adaptations here to efficient walking,
0:31:58 > 0:32:02but there are also some surprising changes in this skeleton,
0:32:02 > 0:32:05which don't seem to be related to walking at all.
0:32:05 > 0:32:08He has very large knees
0:32:08 > 0:32:10and big hips as well,
0:32:10 > 0:32:13and in the trunk, he's got a waist -
0:32:13 > 0:32:17he's got a long, narrow waist - the first time we've seen this.
0:32:17 > 0:32:21His shoulders have also dropped down away from the head,
0:32:21 > 0:32:23and on the back of his skull,
0:32:23 > 0:32:29there's the sign of attachment of a very special ligament.
0:32:29 > 0:32:34Now, all of those changes are to do with stabilising the trunk -
0:32:34 > 0:32:37not something you really need while you're walking.
0:32:37 > 0:32:41So what was this boy doing that destabilised him?
0:32:52 > 0:32:53'The best place in the world
0:32:53 > 0:32:56'to understand Nariokotome Boy's mysterious physique
0:32:56 > 0:33:01'is not in Africa, but in Boston, at Harvard University.'
0:33:09 > 0:33:11I've agreed to be the subject in an experiment,
0:33:11 > 0:33:15so I'm wearing a gym kit and these rather odd items of footwear,
0:33:15 > 0:33:18which are more like gloves than shoes,
0:33:18 > 0:33:22but in them I'm effectively barefoot, like our ancestors.
0:33:26 > 0:33:29'This is the lab of Professor Dan Lieberman.'
0:33:29 > 0:33:301.2m a second.
0:33:30 > 0:33:33Here we go. Three, two, one.
0:33:34 > 0:33:38'His ground-breaking research has revealed that the shape
0:33:38 > 0:33:41'and structure of our bodies has been profoundly affected
0:33:41 > 0:33:46'by a particular form of locomotion.'
0:33:46 > 0:33:49Just pretend you're strolling along the African savannah.
0:33:49 > 0:33:52All of a sudden, you've decided you have to run.
0:33:52 > 0:33:56Maybe there's a kudu up ahead to chase - "OK, it's dinner."
0:33:56 > 0:33:58We're going to get you up to a nice running speed,
0:33:58 > 0:34:00maybe about a ten minute mile.
0:34:00 > 0:34:02All right. Are you ready to speed up?
0:34:02 > 0:34:03Yep, yep.
0:34:03 > 0:34:05Here we go. Three, two, one.
0:34:11 > 0:34:15All right. Well, you have a nice gait, nice forefoot strike.
0:34:15 > 0:34:18As you're running, you're much less stable than when you're walking.
0:34:18 > 0:34:20You're not falling over...
0:34:20 > 0:34:21Yep.
0:34:21 > 0:34:24..but you ought to be, because every time you hit the ground,
0:34:24 > 0:34:26your body wants to fall forward on your chin.
0:34:31 > 0:34:34'Staying balanced whilst running is hard.
0:34:34 > 0:34:40'As we run, our legs throw our bodies out to the left and right.
0:34:41 > 0:34:45'Our shoulders and arms swing in the opposite direction,
0:34:45 > 0:34:48'to try to keep us on the straight and narrow.
0:34:50 > 0:34:52'But it's not enough -
0:34:52 > 0:34:57'we need another crucial element to stay balanced...
0:34:58 > 0:35:00'..our long, narrow waists.
0:35:02 > 0:35:06'They allow us to twist whilst we run,
0:35:06 > 0:35:11'which is vital to counteracting the destabilising forces of our legs.'
0:35:12 > 0:35:16Another challenge when you're running is your head.
0:35:16 > 0:35:17Every time you hit the ground,
0:35:17 > 0:35:19your head wants to pitch forward really fast,
0:35:19 > 0:35:23so your arm attaches to a ligament
0:35:23 > 0:35:26that's unique to humans - the nuchal ligament - in the back of your head.
0:35:26 > 0:35:28Just as your head wants to pitch forward,
0:35:28 > 0:35:32the weight of your arm is connected in the mid-line to this ligament,
0:35:32 > 0:35:35and it pulls your head back.
0:35:35 > 0:35:40This ligament isn't huge, but it's vital for keeping us balanced when we run.
0:35:43 > 0:35:49The attachment of that ligament is very obvious in the skull of Nariokotome Boy.
0:35:50 > 0:35:53It fixes on this ridge.
0:35:53 > 0:35:56Like us, it seems he had a nuchal ligament
0:35:56 > 0:36:00to stop his head pitching forward whilst he ran.
0:36:02 > 0:36:06So all these different parts of our anatomy - our long waists,
0:36:06 > 0:36:10low shoulders and the nuchal ligament in the back of our neck,
0:36:10 > 0:36:13seem to be adaptations to running.
0:36:13 > 0:36:16They were there in Nariokotome Boy.
0:36:16 > 0:36:21Our basic body plan goes back nearly two million years.
0:36:21 > 0:36:24But there's one other really important bit of anatomy
0:36:24 > 0:36:29when it comes to running, and that's in our bums.
0:36:33 > 0:36:39You know what's nice about this? I'm not the person on the treadmill! Usually it's me.
0:36:39 > 0:36:41'And it's not a bone, but a muscle.
0:36:41 > 0:36:44'It's called the gluteus maximus.'
0:36:44 > 0:36:48- We'll put electrodes on your gluteus maximus.- Yep. - The largest muscle in your body.
0:36:48 > 0:36:52- There are different portions and we want to get the upper portion. - Brilliant. On both sides?
0:36:52 > 0:36:56- On both sides. Both cheeks. - And I can use this stuff to get a good contact?
0:36:56 > 0:36:57That's good, yeah.
0:36:57 > 0:36:59'To see what effect the muscle has,
0:36:59 > 0:37:02'I need to be wired up with some electrodes.'
0:37:02 > 0:37:06And I expect that...they won't be filming you as you put these on.
0:37:06 > 0:37:09- No, you WON'T be filming me as I put these on!- All right.
0:37:16 > 0:37:21So, with my bottom fully wired up,
0:37:21 > 0:37:24and Professor Lieberman at the controls of the treadmill...
0:37:24 > 0:37:26Go!
0:37:26 > 0:37:29..it's time to fire up my gluteus maximus.
0:37:34 > 0:37:37To begin with, all I need to do is walk.
0:37:39 > 0:37:42And then Professor Lieberman turns up the power.
0:37:44 > 0:37:48- I'm going to bring you up to a run. - OK.- A nice slow run.
0:37:52 > 0:37:57Every time this muscle contracts, a signal is sent to the computer.
0:37:57 > 0:38:01The stronger the contraction, the larger the signal.
0:38:08 > 0:38:11All right, you can stop.
0:38:11 > 0:38:13I'm going to stop you now.
0:38:13 > 0:38:16The differences between how my gluteus maximus works
0:38:16 > 0:38:19when I'm walking compared with when I'm running
0:38:19 > 0:38:21are displayed on the computer screen.
0:38:21 > 0:38:27So, this is you walking, right? And this is your left gluteus maximus in red,
0:38:27 > 0:38:29and your right in green.
0:38:29 > 0:38:33And you can see that when your right foot hits the ground in a walk,
0:38:33 > 0:38:35- right at this moment, right here in time...- Yep.
0:38:35 > 0:38:38Your gluteus maximus turns on just a little bit.
0:38:38 > 0:38:41And it's basically acting to push your leg back as you're walking.
0:38:41 > 0:38:42OK.
0:38:42 > 0:38:45OK, so now let's go to you running.
0:38:45 > 0:38:47Bam. So here's walking, here's running, and you can see
0:38:47 > 0:38:51the gluteus maximus, how much harder it's working. An enormous effect.
0:38:51 > 0:38:56You don't really need your gluteus maximus to walk, but you can't run without it.
0:38:56 > 0:39:00So really, in order to be a good runner, you have to have a good, strong butt.
0:39:00 > 0:39:04You cannot run very easily as a biped without a big gluteus maximus.
0:39:08 > 0:39:10So, the muscles in my bottom...
0:39:13 > 0:39:15..your bottom...
0:39:15 > 0:39:19and every human bottom on Earth...
0:39:22 > 0:39:24..have been shaped by the fact
0:39:24 > 0:39:28that our ancestors evolved a body built to run.
0:39:30 > 0:39:35But this running body wasn't built for raw speed.
0:39:35 > 0:39:39It evolved to run long distances.
0:39:39 > 0:39:43Our ancestors were endurance runners.
0:39:46 > 0:39:48In a developed country,
0:39:48 > 0:39:52so few of us run on a regular basis that it really is remarkable
0:39:52 > 0:39:57to reflect how much our bodies have been shaped by running.
0:39:57 > 0:39:59And I think even the fittest amongst us
0:39:59 > 0:40:02lead a relatively sedentary lifestyle
0:40:02 > 0:40:07compared with our ancient ancestors, for whom running wasn't a choice,
0:40:07 > 0:40:12it wasn't a recreational activity, it was essential to survival.
0:40:16 > 0:40:18Being able to run long distances could have given
0:40:18 > 0:40:21Nariokotome Boy an important advantage.
0:40:24 > 0:40:28He could hunt, or compete with other scavengers for meat.
0:40:31 > 0:40:33But running in this hot environment
0:40:33 > 0:40:37may have changed our bodies in other unexpected ways.
0:40:58 > 0:41:00In the searing heat of the African savannah,
0:41:00 > 0:41:04running for any length of time can be deadly.
0:41:07 > 0:41:10Keeping cool is critical to survival.
0:41:12 > 0:41:17Other animals lose heat and control their core body temperature
0:41:17 > 0:41:20by panting, and by avoiding the hottest part of the day.
0:41:22 > 0:41:25Few animals hunt in the midday sun.
0:41:28 > 0:41:33But it's thought our ancestors were able to exploit this niche,
0:41:33 > 0:41:37because they developed something incredibly effective.
0:41:37 > 0:41:41SHE PANTS
0:41:41 > 0:41:45One of the really important ways that we keep cool
0:41:45 > 0:41:48whilst running is this - sweat.
0:41:53 > 0:41:55'But in order for sweating to work,
0:41:55 > 0:42:00'we needed to lose our ape-like body hair.'
0:42:01 > 0:42:05One of the most obvious differences between us and other apes
0:42:05 > 0:42:07is our hairlessness, but in fact
0:42:07 > 0:42:10we're not really naked apes at all,
0:42:10 > 0:42:13because our bodies are covered in these very tiny, fine hairs.
0:42:13 > 0:42:17So maybe it's more accurate to say that we are furless.
0:42:19 > 0:42:22And amongst those fine hairs on our skin are the pores
0:42:22 > 0:42:25of up to four million sweat glands,
0:42:27 > 0:42:31which can pump out as much as three litres of sweat an hour.
0:42:35 > 0:42:38So combined with that furlessness,
0:42:38 > 0:42:40this means that we can very effectively
0:42:40 > 0:42:42and efficiently lose body heat
0:42:42 > 0:42:47from the surface of our skin, through the evaporation of sweat.
0:42:47 > 0:42:49Now, when you're running,
0:42:49 > 0:42:52you're generating much more internal body heat
0:42:52 > 0:42:55than you do whilst walking, and when you're running in a hot place
0:42:55 > 0:43:00like this, the need to get rid of all that heat is even more pressing.
0:43:00 > 0:43:02So this combination of furlessness
0:43:02 > 0:43:05and sweatiness has been put forward
0:43:05 > 0:43:09as just one of the physical adaptations that evolved
0:43:09 > 0:43:12in our ancestors for endurance running.
0:43:17 > 0:43:22And that means, in the heat and over a long distance, we can run down
0:43:22 > 0:43:28any animal on the planet, because we can keep cool and they can't.
0:43:32 > 0:43:37Our long distance runner's body became our secret weapon.
0:43:42 > 0:43:47It took nearly five million years of evolution to get from Toumai
0:43:47 > 0:43:49to Nariokotome Boy.
0:43:52 > 0:43:53In that time,
0:43:53 > 0:43:58our ancestors had abandoned the forest for the savannah,
0:43:58 > 0:44:04and had gone from being four-limbed climbers to two-legged runners.
0:44:10 > 0:44:15And standing up on two legs had an important knock-on effect.
0:44:15 > 0:44:16It freed up our arms.
0:44:18 > 0:44:22The anatomy of our legs was completely transformed
0:44:22 > 0:44:26as our ancestors became consummate runners and walkers.
0:44:26 > 0:44:30But what about our arms and our hands?
0:44:30 > 0:44:32I've got a really mobile shoulder.
0:44:32 > 0:44:39I have a forearm which I can rotate 180 degrees, and a grasping hand.
0:44:39 > 0:44:43Now, these are all relics of our tree living ancestry,
0:44:43 > 0:44:46but we took those old adaptations
0:44:46 > 0:44:49and used them for something completely new,
0:44:49 > 0:44:53something that, in turn, would shape our future.
0:44:55 > 0:44:57And that was making tools.
0:45:04 > 0:45:10As far as we know, the first stone tool maker was Homo habilis,
0:45:10 > 0:45:15appearing around two and a half million years ago.
0:45:15 > 0:45:19And every human species since has refined and developed
0:45:19 > 0:45:21that tool-making ability.
0:45:24 > 0:45:27But we aren't the only animals who use tools.
0:45:29 > 0:45:35So what is it about being human that makes our tools so special?
0:45:43 > 0:45:47To find out, I've come to the Uganda Wildlife Education Centre.
0:45:47 > 0:45:52Hello, I've got stuff in my pockets here. Hello!
0:45:54 > 0:45:57Hello, little one. Hello, hello, hello.
0:45:57 > 0:46:00'This is a place of sanctuary for young chimpanzees
0:46:00 > 0:46:02'rescued from poachers.'
0:46:02 > 0:46:04He's biting me. Oh, hello.
0:46:05 > 0:46:09'I'm here to see how they use tools, but they just want to play.'
0:46:12 > 0:46:15No, no, don't look at that, don't look up there.
0:46:15 > 0:46:18So this is Nipper, who's three-and-a-half
0:46:18 > 0:46:22and has about as much energy as a human toddler, I would say.
0:46:22 > 0:46:26You don't want to walk, do you? You want to be carried.
0:46:26 > 0:46:28Come on, then, Nipper.
0:46:28 > 0:46:32'As part of their rehabilitation, the chimps here are encouraged to
0:46:32 > 0:46:36'do things they naturally do in the wild.'
0:46:36 > 0:46:37What's this on here?
0:46:37 > 0:46:39'One of them is termite fishing.'
0:46:39 > 0:46:41Look at that.
0:46:41 > 0:46:44'The centre has built this concrete copy of a termite mound,
0:46:44 > 0:46:47'which is full of honey, rather than insects.'
0:46:47 > 0:46:50This little three-and-a-half-year-old
0:46:50 > 0:46:53certainly knows what he's up to.
0:46:53 > 0:47:00Look at that. He's poking this twig into the hole,
0:47:00 > 0:47:04and then pulling it back out again with honey on it.
0:47:07 > 0:47:10There's no doubt these chimps can use tools,
0:47:10 > 0:47:13but it falls a little short of human tool use,
0:47:13 > 0:47:16and this might be linked to the way they hold them.
0:47:16 > 0:47:20If I was holding this twig, I'm choosing to hold it like that,
0:47:20 > 0:47:24and pushing my thumb down to anchor it on my hand.
0:47:24 > 0:47:26Nipper is holding it like that.
0:47:28 > 0:47:30It's less dexterous,
0:47:30 > 0:47:34and it's actually more difficult to guide the twig in.
0:47:35 > 0:47:41So could the secret to human tool use be in the way we use our hands?
0:47:46 > 0:47:49Our hands move with incredible precision.
0:47:50 > 0:47:54They contain a quarter of the bones in the body.
0:47:54 > 0:47:59Surprisingly, our fingers themselves have few muscles in them,
0:47:59 > 0:48:02they're mainly moved by tendons from the forearm.
0:48:03 > 0:48:07Yet anatomically, our fingers and thumbs are very similar
0:48:07 > 0:48:11to those of our chimpanzee cousins.
0:48:11 > 0:48:14The extraordinary thing about chimpanzee hands
0:48:14 > 0:48:17is when you look at them, they look quite similar to ours.
0:48:17 > 0:48:20And in inside, they've got the same bones, the same muscles.
0:48:20 > 0:48:23So why do we use them so differently?
0:48:23 > 0:48:27There must be something going on which makes our hands unique,
0:48:27 > 0:48:31and uniquely able to make and use tools.
0:48:41 > 0:48:43To unlock the mystery of the human hand,
0:48:43 > 0:48:48I've come to the capital of the United States, Washington DC.
0:48:50 > 0:48:55Here, new research is shedding light on the evolution of our hands.
0:49:11 > 0:49:14This is Professor Brian Richmond.
0:49:14 > 0:49:16And for his test, I need to have one of my hands wrapped up
0:49:16 > 0:49:20in some very technical electronic equipment.
0:49:20 > 0:49:23OK. Does that feel awfully tight?
0:49:23 > 0:49:27You probably won't be extending it all the way back like this.
0:49:27 > 0:49:30This very strange glove-like contraption looks like
0:49:30 > 0:49:34I'm about to play a bizarre virtual reality computer game.
0:49:34 > 0:49:37But in fact, these blue strips are pressure transducers,
0:49:37 > 0:49:38which are going to allow me
0:49:38 > 0:49:44to capture information about how my hand works in real time.
0:49:44 > 0:49:48And you can see it on the screen behind me.
0:49:49 > 0:49:51The special strips in the glove
0:49:51 > 0:49:55measure the pressure I'm generating through each of my fingers.
0:49:55 > 0:50:00From left to right on the screen, you can see the force applied
0:50:00 > 0:50:07to the little finger, ring, middle finger, index finger and thumb.
0:50:07 > 0:50:10The bones and joints of our hands, the muscles
0:50:10 > 0:50:14and the nerves that supply them, are set up in such a way
0:50:14 > 0:50:19that we have incredibly fine control over the movement of our hands.
0:50:19 > 0:50:23But it's not really about moving our hands freely in space,
0:50:23 > 0:50:27it's about the pressure that we can apply to objects.
0:50:30 > 0:50:34That looks so easy, but tell that to a chimpanzee.
0:50:36 > 0:50:41Chimpanzees usually hold a piece of fruit in two hands to eat it.
0:50:41 > 0:50:45They don't seem to be able to apply enough pressure with their fingers
0:50:45 > 0:50:49to bite into it whilst holding it with just one hand.
0:50:49 > 0:50:53In chimpanzees, all of the fingers are very firmly attached
0:50:53 > 0:50:56within the hand. But in our hand, the third is firmly attached
0:50:56 > 0:51:00and the others are more mobile, particularly the fifth finger.
0:51:00 > 0:51:02So we can move that little finger within the hand
0:51:02 > 0:51:07much more than an ape can, and we can even rotate that little finger around
0:51:07 > 0:51:11to meet the thumb. It's almost like having a thumb on the other side.
0:51:11 > 0:51:13It's facing the thumb across the palm.
0:51:13 > 0:51:16Precisely. It lets you grasp around an object.
0:51:16 > 0:51:21So, with my electronic glove fully activated,
0:51:21 > 0:51:25it's time to test just how powerful my flexible little finger is.
0:51:25 > 0:51:29And look at that. You can see the pressure on your little finger,
0:51:29 > 0:51:30and your thumb on the other side.
0:51:35 > 0:51:40Our hands are so mobile that they can conform in any variety of ways
0:51:40 > 0:51:44to handle any variety of objects, and that's what makes our hands special
0:51:44 > 0:51:46compared to the hands of other monkeys and apes.
0:51:46 > 0:51:52But there's something else we have and chimpanzees don't.
0:51:52 > 0:51:55It's very obvious when you compare the bones.
0:51:55 > 0:52:00The thumb in a human hand is just so much longer and thicker.
0:52:00 > 0:52:03If you think of how powerful a chimpanzee's hand is,
0:52:03 > 0:52:05ironically, the thumb is quite weak
0:52:05 > 0:52:09- compared to the big powerful thumb that we have.- Yeah.
0:52:09 > 0:52:15'But that big thumb is a relatively new bit of anatomy.
0:52:15 > 0:52:20'It's only been around for the last two and a half million years.
0:52:20 > 0:52:23'And it first appears in Homo habilis,
0:52:23 > 0:52:26'our ancestor who made those early stone tools.
0:52:28 > 0:52:32'It seems more than a coincidence that big thumbs appear
0:52:32 > 0:52:34'at the same time as stone tools,
0:52:34 > 0:52:38'and it's always been thought that the two are linked.
0:52:38 > 0:52:44'Fortunately, we have the technology to put that theory to the test.'
0:52:44 > 0:52:48OK, I'm ready. I've got the hammer stone in my hand
0:52:48 > 0:52:51that's strapped up to the monitors, so stand well back.
0:52:51 > 0:52:52OK.
0:52:55 > 0:52:57There you go, good.
0:52:59 > 0:53:03So, if our big thumbs are important for making stone tools,
0:53:03 > 0:53:07you'd expect to see a large pressure spike on the screen for my thumb.
0:53:11 > 0:53:14What was actually going on with my fingers and thumbs?
0:53:14 > 0:53:18So we can see right here that you have force on your thumb,
0:53:18 > 0:53:22but you have just as much force on your other fingers as well.
0:53:22 > 0:53:25We don't see particularly high force on the thumb.
0:53:25 > 0:53:30Why on Earth, then, did our thumb become so big and strong?
0:53:30 > 0:53:32If it's not making stone tools,
0:53:32 > 0:53:34could it be linked to how we use them?
0:53:36 > 0:53:39Let's see what happens when I cut some meat.
0:53:39 > 0:53:42That's great. You can see it's sharp, it's really cutting.
0:53:42 > 0:53:46It's incredible, yeah. Look at that.
0:53:46 > 0:53:49OK, and let's see how your thumb's doing.
0:53:49 > 0:53:52Oh, look at that. The thumb pressure is very high.
0:53:52 > 0:53:56It's as high or higher than it is on the fingers.
0:53:58 > 0:54:03That's interesting. It's a very different pattern from when I was making the tools.
0:54:03 > 0:54:07Absolutely, and that tells us that your thumb is having
0:54:07 > 0:54:10to really forcefully pinch that tool while it's being used.
0:54:10 > 0:54:13And that's not what we saw when you made a tool.
0:54:13 > 0:54:15So this tells us that maybe it's using a tool
0:54:15 > 0:54:18that helps explain the evolution of a robust thumb,
0:54:18 > 0:54:20instead of making a tool.
0:54:24 > 0:54:28For the first time, it's becoming clear
0:54:28 > 0:54:31that it's how our ancestors used the tools they made
0:54:31 > 0:54:33that shaped our anatomy.
0:54:37 > 0:54:42The bones in our hands developed as our ancestors' behaviour changed.
0:54:44 > 0:54:46It's fascinating to look at the shape
0:54:46 > 0:54:48and the function of our hands today,
0:54:48 > 0:54:53and to realise how that has been brought about through evolution.
0:54:53 > 0:54:56We think about our thumbs being so important,
0:54:56 > 0:55:00but it turns out our little fingers are incredibly important as well.
0:55:00 > 0:55:05And what's really amazing is that our hands have changed
0:55:05 > 0:55:08because of something that we've done. It's not just
0:55:08 > 0:55:10about adapting to our environment,
0:55:10 > 0:55:13it's about adapting to things that we've made.
0:55:13 > 0:55:18The tools that we have created have shaped our hands.
0:55:22 > 0:55:28And that ability to use tools didn't just transform our anatomy,
0:55:28 > 0:55:30it utterly changed our world.
0:55:40 > 0:55:44Dexterous and powerful hands were fundamentally important
0:55:44 > 0:55:47to the success of our ancestors.
0:55:52 > 0:55:54Our species, Homo sapiens,
0:55:54 > 0:55:59only appeared on the planet around 200,000 years ago,
0:55:59 > 0:56:03but we are the most successful human species ever.
0:56:09 > 0:56:12With our hands, we could make the tools
0:56:12 > 0:56:16and technology which allowed us to colonise every corner of the globe.
0:56:22 > 0:56:25But they also enabled us to do much more than that.
0:56:31 > 0:56:35They gave us the means to transform the world around us.
0:57:12 > 0:57:16But it all started back in Africa,
0:57:16 > 0:57:19with an ape who got up on two legs and walked.
0:57:26 > 0:57:30Our bones and muscles form the foundations of two fundamentally
0:57:30 > 0:57:37human characteristics. We are bipedal apes and we are tool makers.
0:57:37 > 0:57:41On our long legs, we strode out of our continent of origin
0:57:41 > 0:57:44and went on to colonise the globe.
0:57:44 > 0:57:48But the dexterity of our hands enabled us to make tools
0:57:48 > 0:57:52and transform our environment.
0:57:52 > 0:57:54And I think it's really humbling
0:57:54 > 0:57:58to realise that our greatest achievements,
0:57:58 > 0:58:02our most advanced technology, soaring architecture,
0:58:02 > 0:58:04exquisite art and music,
0:58:04 > 0:58:11they all depend on an unpredictable series of anatomical adjustments
0:58:11 > 0:58:13that changed our ancestors
0:58:13 > 0:58:19into walkers and runners and sculpted the hand of the tool maker.
0:58:47 > 0:58:50Subtitles by Red Bee Media Ltd
0:58:50 > 0:58:54E-mail subtitling@bbc.co.uk