Origins of Us (2011): Season 1, Episode 1 - Bones - full transcript

The shape of your face...

Walking on two legs...

The way you see the world...

What makes you the person you are?

The story of each
and every one of us

can be traced back millions of years
to the plains of ancient Africa.

The answers to the question,
"What makes us human?"

lie buried in the ground
in the fossils and other traces
of our ancestors,

but also lie deep within
our own bodies, in our bones,
flesh and genes.

As an anatomist, I'm fascinated
by the way our bodies

have been sculpted



by our ancestors' struggle
for survival.

But why did we leave behind
the other apes in the forest...

..and stride out
into the African savannah?

How did that change
the way we looked...

..give us big muscles
in the unlikeliest of places...

..and help us to acquire
amazing new skills?

The story of how we became human
describes how forest-dwelling apes
evolved into us

and the story
starts millions of years ago,

with an ape who stood
upright and walked.

Our story began around
six million years ago,

with apes who lived
in an ancient African forest.

In many ways, they would have been
similar to the apes

that still live in the forests
here today.

I'm here in the ancient
forest of Kibale in Uganda,



which covers about
700 square kilometres,

and I'm hoping to do
something really special,

and that's to track down
some of our closest living
relatives - chimpanzees.

I want to get close enough
to see how their bodies work,

but getting near to the wild chimps
who live in this dense, wet forest
isn't easy.

'Francis Mugurusi is my guide.'

Hello, where are the chimpanzees?

'He's been studying the chimps here
for nearly 20 years.'

I think we're getting close now.

Francis, my guide, tells me that
he can hear the chimpanzees.

He thinks there's two groups,
one further away over there,

but also a group which
is much nearer, perhaps only
five or ten minutes away.

So this is really exciting.

CHIMPS SQUEAL IN THE DISTANCE

CHIMP CALLS

SEVERAL CHIMPS CALLING

Oh, there's lots of them,
they're all around us.

This is just extraordinary.

This is my first sight
of chimpanzees in the wild.

It's impossible to look
at chimpanzees and think that
we're not related to them.

Of course, they are
our closest living relatives.

I mean, look at the way
he's sitting there.

We are so closely related
to chimpanzees,

we share nearly 99%
of our DNA with them.

BREAKING WIND

I just want to say, that's not me.

But although
we're genetically close,

we are not descended from them.

Looking at chimpanzees helps us
understand where we've come from

and that's not because we've evolved
from them, of course we haven't,

but if we trace back each
of our family trees far enough

we reach a point
where they come together.

We have a common ancestor
with chimpanzees,

going back about six or seven
million years ago.

So I'm here visiting my relatives.

Now, their ancestors stayed in
the forests, whereas ours moved out.

And if we can find out how
and why we did that,

well, that's the story
of how we became human.

Our evolutionary journey
is written into our bodies

and into the way we use them.

And a chimpanzee's body is built for
a particular way of getting around.

(He's fast asleep.)

Literally, just a few metres away.

He's just having a quick look
around, but basically he's dozing,

lying on his back
with his limbs splayed out.

He's got these wonderfully long arms

and very short legs -
he's a climber.

And his feet are wonderful.

He's still got this grasping ability
in his feet that we've lost.

He's able to grip onto things
and climb.

His great toe, his big toe,
is out to the side like that,

so it makes his feet
look like hands.

'Millions of years ago,

'our ancestors would have had feet
which grasped like this.'

And that's something
that we've lost.

'In six million years, our body plan
has become very different,

'with our long legs
and feet for walking on.'

SHE PANTS

It look as though they've moving
quite slowly, but I can assure you
they're not.

This is a fairly fast pace
to be moving through the jungle.

'So what was it that set our
ancestors off on a different path,

'a path that would lead us
to colonise the globe,

'whilst other apes
stayed in the African forest?

'And when did we start to change?'

It's always been a puzzle.

Until this extraordinary fossil
was discovered just a few years ago.

This is Toumai, also known
as sahelanthropus tchadensis,

and it's not putting it too strongly
to say that his discovery
caused something of a stir.

He certainly looks like an ape,
and just to convince you of that,

I've got a modern chimpanzee skull

and you can see
how similar the two are.

They've even got
a similar sized brain.

But there's something
very special about Toumai.

And just to explain that,
first of all I want to show you

the foramen magnum underneath
the chimpanzee skull.

This is where the spinal cord
exits the skull.

If I hold the chimpanzee skull
in that orientation,

as the skull would be in life,

with the eye sockets
in a vertical plane,

we can see that the foramen magnum
exits the skull at this angle.

In Toumai
it's completely different.

The foramen magnum is right
underneath the skull,

which means the skull is balancing
on an erect spine.

This isn't any old ape.

This is an ape who stood
upright on two legs.

And not only that,
this is a bipedal ape,

who dates to six to seven
million years ago.

This is a hugely significant
moment in our story.

It means that Toumai
was moving around on two legs,

very close to the time our ancestors
split from chimpanzees.

There's no question
he's more chimpanzee-like than human

but Toumai puts standing up
right at the start of our journey.

In the six million years
since Toumai stood upright,

our skeleton has undergone
many changes.

Our bones and muscles
have been transformed

by this new way of getting around,
upright, on two legs.

I'm a human anatomist - I've studied
the structure of the human body

and I've mainly done
that through dissection.

And in fact,
that's exactly what anatomy means,

it means to take apart.

But today I'm trying out something
a bit different.

I'm putting the human body,
or at least the skeleton,
back together again.

This skeleton is,
as you might expect, white,

but in fact
that's because these are dead bones.

Living bones are pink
because they're full of blood.

Anybody that's broken a bone
will know that.

A fractured bone bleeds like crazy.

Living bone in our bodies
constantly changes

in response to the stresses
and the strains we place it under.

So, over a period of years,
all of the bone in your skeleton

is taken away
and replaced with new bone.

But standing up on two legs

is dependent on a central
yet vulnerable part of our anatomy.

Right in the centre of the skeleton
is this wonderful structure,

the spine, built up
of a series of repeating vertebrae,

and it forms
this beautiful double-S shape.

But all of this anatomical beauty
comes at a cost.

With this isolated spine,
you can see the curves beautifully,

but you can see something else,

and that's the increase in size
of the vertebrae as we go down,

until we get to here,
the lumbar spine,

where the vertebrae
are absolutely massive.

And that's because they're bearing
the weight of everything above them.

So it's not surprising

that this is where we tend
to get problems with our spines,

and, in fact, it's the most common
reason for visits to GPs.

As we get older, the intervertebral
discs start to dry out,

and the inside of them can pop out
and press on the spinal nerves,

and that can be painful.

And also the weight that is borne
by the spine moves backwards

and now is loaded onto these joints
at the back,

so they can be painful, too.

So if standing upright causes us
so many problems, why did we do it?

The answer is locked away
in the dark recesses of time.

Six million years ago,

the world's climate
was becoming colder and drier,

and the forests of Africa
were thinning out.

And where dense jungles
gave way to woodlands,

the apes who lived in them
started to change.

BARKING AND CHATTER OF CHIMPANZEES

You can see what might have happened
by looking at apes living today.

'Up in the trees,

'some of the best food
is in the most inaccessible places.

'And being able to reach the highest
branches is an obvious advantage.'

They are feeding on a fruit.

It's one of their
favourite fruits that they feed on.

So they're eating fruits up there?

Yes, they're eating ripe fruits,
and there are some that have fallen

with the leaves and branch here.

Oh, right, yeah. Can I taste it?
Yes, we can taste.

So the little yellow ones are ripe?
Yes, they are ripe, and they like it.

Mmm.

It's somehow bitter. It is bitter.

But for them, they like it.

It's not one of my favourite fruits.
It can't be your favourite.

CHIMPANZEES HOOT AND SCREECH

In an increasingly patchy woodland,

being able to stand to reach fruit
on the thinnest branches

must have been a great advantage
for our ancestors.

And it's possible that this is what
drove the changes in Toumai's body.

He could have been standing upright
in the trees.

The latest discoveries

show that Toumai
was the first of many bipedal apes.

Over the next two million years,

fossils like Orrorin tugenensis
and Ardipithecus ramidus

show that other apes
were also adapting

to their changing environment
by standing upright.

They were still essentially climbers
but as the forests thinned,

it's thought these apes were
spending more time on the ground.

It's hard to know exactly when

our ancestors gave up a life in
the trees for living on the ground.

But there is a clue,
hidden away in our bones.

I've been watching the chimpanzees
climbing,

and the way their ankles work,

so I want to compare that
with my ankle.

Sorry about this, but the boot
and the sock are coming off.

Now most of the time
I'm walking around on the ground,

and my foot is at 90 degrees
to my leg.

But I can move the ankle like this,

that's called dorsiflexion,

to about 20 degrees.

Now compare that with chimpanzees.

To climb efficiently
on something vertical,

you need to be able to bend
your foot up much more than we can.

When chimps are climbing,

they dorsiflex their ankles
up to 45 degrees.

The differences in ankle movement
between us and them

could provide vital evidence
in working out

exactly when our ancestors
gave up climbing for walking.

To nail down when we became
walking rather than climbing apes,

scientists at Boston University
have been studying the bones

of our ancient ancestors
with laser-like precision.

They've analysed the remains
of every fossil

they could lay their hands on...

..including the bones of
this truly remarkable fossil - Lucy.

She belongs to a species
called Australopithecus afarensis.

This is a replica of Lucy,
who is one of the most famous,

if not THE most famous skeletons
in the whole of human evolution.

She's 3.2 million years old,
and we have so much of her skeleton

that we can tell an enormous amount
about her.

She would have stood
just over a metre tall.

The length of her arms
and her curved fingers

suggest that climbing
was still really important

in the way she got around.

But recent research
is challenging that idea.

There's one area of Lucy's skeleton

that's been the focus of Jeremy
DeSilva's exciting new research.

Lucy has a spectacular ankle, uh...
and we have some comparisons.

Great, so this is a chimp.

Right, and this is a human,
and chimpanzees,

they do remarkable things
with their feet and ankles.

They could take the top of their foot

and press it right
up against their shin.

It's amazing flexion,
which if you and I tried that,

we'd snap ligaments and our Achilles,
we just aren't equipped for that.

A big ape like a chimpanzee,

putting all of its body on the foot
and on the ankle

while it's climbing like that,
leaves its mark on the bones.

On the left is the bottom
of a chimpanzee's tibia,

or shin bone, where it
forms the ankle joint,

and there's a very
obvious trapezoid shape.

On the right is the same area
of the human tibia,

and it's square.

The shape of your bones reflects

whether you use your ankles
for climbing or for walking.

OK, so...let's have a look at Lucy
and compare her.

Well, although she's tiny,

the shape of that joint just there

is much more human-like. It is.

And that tells us that her feet
were planted firmly on the ground

directly underneath her knees,

the adaptations we see
in upright-walking creatures.

Fantastic. Like us.

Amazing to be able to tell so much
just from the end of one bone. Yes.

And the magnificent thing about Lucy
is that we have so many bones,

and each one of those bones
tells a fascinating story.

Lucy still appears very ape-like,

and her brain was similar in size
to that of a chimpanzee's.

But becoming a walking ape

had fundamentally changed
the shape of her body.

By the time we see
Australopithecines like Lucy,

we can be absolutely sure
beyond a shadow of a doubt,

that our ancestors were standing
and walking around on two legs.

And not only that,
they were committed to walking.

It was their main way
of getting around.

'Giving up climbing for walking
suggests that our ancestors

'were moving beyond
the confines of the forest,

'that they were exploring
new habitats.

'But walking is a physical skill
that takes time to learn.

'Just think about
what these babies are trying to do.

'Balancing on their tiny little
feet, defying gravity.

'Some of us get the hang of it
quicker than others.

'And some of us
aren't in a rush to do anything.

'But most of us will, at some stage
in our early childhood,

'stagger to our feet and walk.'

These little ones are just learning

to do something
that's incredibly difficult.

They've been quite happy for a few
months crawling around on all fours,

but now they really want to get up
onto two feet and start walking.

And at any point in time,
when she cracks it,

she'll be balancing on
just one foot.

'And with each step, this involves
coordinating some 200 muscles.

'It's an amazing feat of learning,
but there are physical changes too.

'As these toddlers learn to walk,
their bodies are changing.'

They're using their muscles
in different ways,

and the muscles will develop
accordingly.

And deep inside their bodies,
their bones are changing as well.

They'll start to develop the
backwards curve in the lower spine

and the bottom of the spine will
push down between the two hip bones.

The hip bones curve forwards,

and the thigh bone also starts
to curve forwards and bend inwards.

But what's really interesting
is that we don't know

how much these changes
are programmed,

and how much they're appearing,

they're developing,
in response to walking.

Ooh! And jumping.

'It's obvious that the evolution
of walking

'has had a profound impact
on our bodies.

'And it all started with those
ancestors who put one foot

'in front of the other.'

It took millions of years
for our ancestors

to master the art of standing
and then walking.

But walking would fundamentally
alter the course

of our evolutionary history.

And the next critical step
on the long road to becoming human

was driven by a new wave
of drastic climate change.

From around three million years ago,
East Africa started to dry

and the forests shrank back.

A brand-new habitat was born -
the savannah.

This was a whole new world,
rich with opportunity,

and evolution went into overdrive.

There was an explosion of species
taking advantage

of the expanding grasslands.

And alongside them
were new species of walking apes,

who strode out on two legs
into the changing landscape...

forming new branches
of our family tree.

Giving up climbing for walking

meant that this group of apes

were in the right place
at the right time.

As the forests receded,
the walking ape came into its own.

In fact, we know from the fossils
that around two million years ago

there were at least
six different species

of these hominines, these apes
which habitually walked on two legs.

It was a big, bushy family tree.

But while most of those lineages
would eventually die out,

one would go on
to be extraordinarily successful.

We don't really know
why any of the others died out,

but the thought that any
of our ancestors could have survived

in this arid, open environment
is difficult to comprehend.

For a relatively puny forest ape,

life on the savannah would surely
have been a dangerous proposition.

I am feeling quite nervous

and extremely vulnerable,
out here on the plain.

I'm keeping my eyes peeled

and I can see some gazelles
over there, and some zebra,

but I know that there are much more
dangerous animals here as well.

I saw some lions earlier,
and a cheetah.

And there would have been similarly
formidable predators here

two million years ago.

So, how did our ancestors survive
on the open savannah?

This extraordinary fossil
skeleton of a young male,

unearthed here in Kenya,

gives us an insight into how
our ancestors

managed not only to survive
but to thrive on the savannah.

I've really enjoyed laying
this skeleton out.

I've seen so many pictures of it

but there's nothing quite like
being able to handle the real thing.

Well, actually, this is a replica,

but it is one of THE most famous
early human fossils.

And it's just remarkable how much
of the skeleton has been preserved,

how many bones we have here.

It dates back to
one-and-a-half-million years ago.

He's called KNM-WT 15000,

or, perhaps more poetically,
Nariokotome Boy.

And his bones tell us
something really important

about a crucial change
to our bodies in human evolution.

There are clues all over
his skeleton,

but the most striking
are in the lower half of his body.

Just look at the length of these
legs. It is stunning.

If I put my leg down
beside Nariokotome Boy's leg,

you can see that it's
practically the same length.

His femur fits along my thigh,

his tibia...

fits quite nicely
along my lower leg there.

And these long legs really are

an important step forward
in human evolution.

This is the first time we've seen
somebody who looks human -

he could be walking out there,
in this landscape,

and you would not notice
that he wasn't one of us.

Nariokotome Boy was a member

of a species of early humans
known as Homo erectus.

He may be nearly
two million years old,

but his body plan was obviously
highly effective,

because from the neck down,
he's so similar to us today.

But his brain was only
two-thirds the size of ours.

He didn't get by on his wits alone.

So is there anything else about him
that can tell us

how he survived out here?

There are plenty of adaptations here
to efficient walking,

but there are also some surprising
changes in this skeleton,

which don't seem to be related
to walking at all.

He has very large knees

and big hips as well,

and in the trunk, he's got a waist -

he's got a long, narrow waist -
the first time we've seen this.

His shoulders have also
dropped down away from the head,

and on the back of his skull,

there's the sign of attachment
of a very special ligament.

Now, all of those changes are to do
with stabilising the trunk -

not something you really need
while you're walking.

So what was this boy doing
that destabilised him?

'The best place in the world

'to understand Nariokotome Boy's
mysterious physique

'is not in Africa, but in Boston,
at Harvard University.'

I've agreed to be
the subject in an experiment,

so I'm wearing a gym kit and these
rather odd items of footwear,

which are more like
gloves than shoes,

but in them I'm effectively
barefoot, like our ancestors.

'This is the lab
of Professor Dan Lieberman.'

1.2m a second.

Here we go. Three, two, one.

'His ground-breaking research
has revealed that the shape

'and structure of our bodies
has been profoundly affected

'by a particular form
of locomotion.'

Just pretend you're
strolling along the African savannah.

All of a sudden, you've decided
you have to run.

Maybe there's a kudu up
ahead to chase - "OK, it's dinner."

We're going to get you up
to a nice running speed,

maybe about a ten minute mile.

All right.
Are you ready to speed up?

Yep, yep.

Here we go. Three, two, one.

All right. Well, you have a nice
gait, nice forefoot strike.

As you're running, you're much
less stable than when you're walking.

You're not falling over...

Yep.

..but you ought to be, because every
time you hit the ground,

your body
wants to fall forward on your chin.

'Staying balanced whilst running
is hard.

'As we run, our legs throw our
bodies out to the left and right.

'Our shoulders and arms
swing in the opposite direction,

'to try to keep us
on the straight and narrow.

'But it's not enough -

'we need another crucial element
to stay balanced...

'..our long, narrow waists.

'They allow us to twist whilst we
run,

'which is vital to counteracting the
destabilising forces of our legs.'

Another challenge when you're
running is your head.

Every time you hit the ground,

your head wants to pitch forward
really fast,

so your arm attaches to a ligament

that's unique to humans - the nuchal
ligament - in the back of your head.

Just as your head wants
to pitch forward,

the weight of your arm is connected
in the mid-line to this ligament,

and it pulls your head back.

This ligament isn't huge,
but it's vital for keeping
us balanced when we run.

The attachment of that ligament
is very obvious in the skull
of Nariokotome Boy.

It fixes on this ridge.

Like us, it seems
he had a nuchal ligament

to stop his head pitching forward
whilst he ran.

So all these different parts
of our anatomy - our long waists,

low shoulders and the nuchal
ligament in the back of our neck,

seem to be adaptations to running.

They were there in Nariokotome Boy.

Our basic body plan goes back
nearly two million years.

But there's one other
really important bit of anatomy

when it comes to running,
and that's in our bums.

You know what's nice about this?
I'm not the person on the treadmill!
Usually it's me.

'And it's not a bone, but a muscle.

'It's called the gluteus maximus.'

We'll put electrodes
on your gluteus maximus. Yep.
The largest muscle in your body.

There are different portions
and we want to get the upper portion.
Brilliant. On both sides?

On both sides. Both cheeks.
And I can use this stuff
to get a good contact?

That's good, yeah.

'To see what effect the muscle has,

'I need to be wired up
with some electrodes.'

And I expect that...they won't
be filming you as you put these on.

No, you WON'T be filming me
as I put these on! All right.

So, with my bottom fully wired up,

and Professor Lieberman
at the controls of the treadmill...

Go!

..it's time to fire up
my gluteus maximus.

To begin with,
all I need to do is walk.

And then Professor Lieberman
turns up the power.

I'm going to bring you up to a run.
OK. A nice slow run.

Every time this muscle contracts,
a signal is sent to the computer.

The stronger the contraction,
the larger the signal.

All right, you can stop.

I'm going to stop you now.

The differences
between how my gluteus maximus works

when I'm walking
compared with when I'm running

are displayed
on the computer screen.

So, this is you walking, right?
And this is your left
gluteus maximus in red,

and your right in green.

And you can see that when your
right foot hits the ground in a walk,

right at this moment,
right here in time... Yep.

Your gluteus maximus turns on
just a little bit.

And it's basically acting to push
your leg back as you're walking.

OK.

OK, so now let's go to you running.

Bam. So here's walking,
here's running, and you can see

the gluteus maximus, how much harder
it's working. An enormous effect.

You don't really need your gluteus
maximus to walk, but you can't run
without it.

So really, in order to be
a good runner, you have to have
a good, strong butt.

You cannot run very easily as a biped
without a big gluteus maximus.

So, the muscles in my bottom...

..your bottom...

and every human bottom on Earth...

..have been shaped by the fact

that our ancestors evolved a body
built to run.

But this running body
wasn't built for raw speed.

It evolved to run long distances.

Our ancestors
were endurance runners.

In a developed country,

so few of us run on a regular basis
that it really is remarkable

to reflect how much our bodies
have been shaped by running.

And I think even the fittest
amongst us

lead a relatively sedentary
lifestyle

compared with our ancient ancestors,
for whom running wasn't a choice,

it wasn't a recreational activity,
it was essential to survival.

Being able to run long distances
could have given

Nariokotome Boy
an important advantage.

He could hunt, or compete with other
scavengers for meat.

But running in this hot environment

may have changed our bodies
in other unexpected ways.

In the searing heat
of the African savannah,

running for any length of time
can be deadly.

Keeping cool is critical
to survival.

Other animals lose heat and control
their core body temperature

by panting, and by avoiding
the hottest part of the day.

Few animals hunt in the midday sun.

But it's thought our ancestors
were able to exploit this niche,

because they developed something
incredibly effective.

SHE PANTS

One of the really important ways
that we keep cool

whilst running is this - sweat.

'But in order for sweating to work,

'we needed to lose
our ape-like body hair.'

One of the most obvious differences
between us and other apes

is our hairlessness, but in fact

we're not really naked apes
at all,

because our bodies are covered
in these very tiny, fine hairs.

So maybe it's more accurate
to say that we are furless.

And amongst those fine hairs
on our skin are the pores

of up to four million sweat glands,

which can pump out as much
as three litres of sweat an hour.

So combined with that furlessness,

this means that
we can very effectively

and efficiently lose body heat

from the surface of our skin,
through the evaporation of sweat.

Now, when you're running,

you're generating
much more internal body heat

than you do whilst walking, and when
you're running in a hot place

like this, the need to get rid of
all that heat is even more pressing.

So this combination of furlessness

and sweatiness has been put forward

as just one of the physical
adaptations that evolved

in our ancestors
for endurance running.

And that means, in the heat and over
a long distance, we can run down

any animal on the planet, because
we can keep cool and they can't.

Our long distance runner's body
became our secret weapon.

It took nearly five million years
of evolution to get from Toumai

to Nariokotome Boy.

In that time,

our ancestors had abandoned
the forest for the savannah,

and had gone from being four-limbed
climbers to two-legged runners.

And standing up on two legs
had an important knock-on effect.

It freed up our arms.

The anatomy of our legs
was completely transformed

as our ancestors became
consummate runners and walkers.

But what about our arms
and our hands?

I've got a really mobile shoulder.

I have a forearm which I can rotate
180 degrees, and a grasping hand.

Now, these are all relics
of our tree living ancestry,

but we took those old adaptations

and used them
for something completely new,

something that, in turn,
would shape our future.

And that was making tools.

As far as we know, the first stone
tool maker was Homo habilis,

appearing around
two and a half million years ago.

And every human species since
has refined and developed

that tool-making ability.

But we aren't the only animals
who use tools.

So what is it about being human
that makes our tools so special?

To find out, I've come to the
Uganda Wildlife Education Centre.

Hello, I've got stuff in my pockets
here. Hello!

Hello, little one.
Hello, hello, hello.

'This is a place of sanctuary
for young chimpanzees

'rescued from poachers.'

He's biting me. Oh, hello.

'I'm here to see how they use tools,
but they just want to play.'

No, no, don't look at that,
don't look up there.

So this is Nipper,
who's three-and-a-half

and has about as much energy
as a human toddler, I would say.

You don't want to walk, do you?
You want to be carried.

Come on, then, Nipper.

'As part of their rehabilitation,
the chimps here are encouraged to

'do things they naturally do
in the wild.'

What's this on here?

'One of them is termite fishing.'

Look at that.

'The centre has built this
concrete copy of a termite mound,

'which is full of honey,
rather than insects.'

This little
three-and-a-half-year-old

certainly knows what he's up to.

Look at that.
He's poking this twig into the hole,

and then pulling it back out again
with honey on it.

There's no doubt these chimps
can use tools,

but it falls a little short
of human tool use,

and this might be linked
to the way they hold them.

If I was holding this twig,
I'm choosing to hold it like that,

and pushing my thumb down
to anchor it on my hand.

Nipper is holding it like that.

It's less dexterous,

and it's actually more difficult
to guide the twig in.

So could the secret to human tool
use be in the way we use our hands?

Our hands move
with incredible precision.

They contain a quarter
of the bones in the body.

Surprisingly, our fingers themselves
have few muscles in them,

they're mainly moved
by tendons from the forearm.

Yet anatomically, our fingers
and thumbs are very similar

to those of our chimpanzee cousins.

The extraordinary thing
about chimpanzee hands

is when you look at them,
they look quite similar to ours.

And in inside, they've got
the same bones, the same muscles.

So why do we use them
so differently?

There must be something going on
which makes our hands unique,

and uniquely able
to make and use tools.

To unlock the mystery
of the human hand,

I've come to the capital
of the United States, Washington DC.

Here, new research is shedding light
on the evolution of our hands.

This is Professor Brian Richmond.

And for his test, I need
to have one of my hands wrapped up

in some very technical electronic
equipment.

OK. Does that feel awfully tight?

You probably won't be extending it
all the way back like this.

This very strange glove-like
contraption looks like

I'm about to play a bizarre
virtual reality computer game.

But in fact, these blue strips
are pressure transducers,

which are going to allow me

to capture information about
how my hand works in real time.

And you can see it
on the screen behind me.

The special strips in the glove

measure the pressure I'm generating
through each of my fingers.

From left to right on the screen,
you can see the force applied

to the little finger, ring, middle
finger, index finger and thumb.

The bones and joints of our hands,
the muscles

and the nerves that supply them,
are set up in such a way

that we have incredibly fine control
over the movement of our hands.

But it's not really about moving
our hands freely in space,

it's about the pressure
that we can apply to objects.

That looks so easy,
but tell that to a chimpanzee.

Chimpanzees usually hold a piece
of fruit in two hands to eat it.

They don't seem to be able to apply
enough pressure with their fingers

to bite into it whilst holding it
with just one hand.

In chimpanzees, all of the fingers
are very firmly attached

within the hand. But in our hand,
the third is firmly attached

and the others are more mobile,
particularly the fifth finger.

So we can move that little finger
within the hand

much more than an ape can, and we can
even rotate that little finger around

to meet the thumb. It's almost like
having a thumb on the other side.

It's facing the thumb
across the palm.

Precisely. It lets you grasp
around an object.

So, with my electronic glove
fully activated,

it's time to test just how powerful
my flexible little finger is.

And look at that. You can see
the pressure on your little finger,

and your thumb on the other side.

Our hands are so mobile that they can
conform in any variety of ways

to handle any variety of objects,
and that's what makes our hands
special

compared to the hands
of other monkeys and apes.

But there's something else
we have and chimpanzees don't.

It's very obvious
when you compare the bones.

The thumb in a human hand
is just so much longer and thicker.

If you think of how powerful
a chimpanzee's hand is,

ironically, the thumb is quite weak

compared to the big powerful thumb
that we have. Yeah.

'But that big thumb is a relatively
new bit of anatomy.

'It's only been around for the last
two and a half million years.

'And it first appears
in Homo habilis,

'our ancestor who made those
early stone tools.

'It seems more than a coincidence
that big thumbs appear

'at the same time as stone tools,

'and it's always been thought
that the two are linked.

'Fortunately, we have the technology
to put that theory to the test.'

OK, I'm ready.
I've got the hammer stone in my hand

that's strapped up to the monitors,
so stand well back.

OK.

There you go, good.

So, if our big thumbs are important
for making stone tools,

you'd expect to see a large pressure
spike on the screen for my thumb.

What was actually going on
with my fingers and thumbs?

So we can see right here
that you have force on your thumb,

but you have just as much force
on your other fingers as well.

We don't see particularly high force
on the thumb.

Why on Earth, then, did our thumb
become so big and strong?

If it's not making stone tools,

could it be linked
to how we use them?

Let's see what happens
when I cut some meat.

That's great. You can see it's sharp,
it's really cutting.

It's incredible, yeah. Look at that.

OK, and let's see
how your thumb's doing.

Oh, look at that.
The thumb pressure is very high.

It's as high or higher
than it is on the fingers.

That's interesting. It's a very
different pattern from when
I was making the tools.

Absolutely, and that tells us
that your thumb is having

to really forcefully pinch
that tool while it's being used.

And that's not what we saw
when you made a tool.

So this tells us that maybe
it's using a tool

that helps explain the evolution
of a robust thumb,

instead of making a tool.

For the first time,
it's becoming clear

that it's how our ancestors
used the tools they made

that shaped our anatomy.

The bones in our hands developed
as our ancestors' behaviour changed.

It's fascinating to look
at the shape

and the function of our hands today,

and to realise how that has been
brought about through evolution.

We think about our thumbs
being so important,

but it turns out our little fingers
are incredibly important as well.

And what's really amazing
is that our hands have changed

because of something
that we've done. It's not just

about adapting to our environment,

it's about adapting to things
that we've made.

The tools that we have created
have shaped our hands.

And that ability to use tools
didn't just transform our anatomy,

it utterly changed our world.

Dexterous and powerful hands
were fundamentally important

to the success of our ancestors.

Our species, Homo sapiens,

only appeared on the planet
around 200,000 years ago,

but we are the most successful
human species ever.

With our hands,
we could make the tools

and technology which allowed us to
colonise every corner of the globe.

But they also enabled us
to do much more than that.

They gave us the means
to transform the world around us.

But it all started back in Africa,

with an ape who got up on two legs
and walked.

Our bones and muscles form
the foundations of two fundamentally

human characteristics. We are
bipedal apes and we are tool makers.

On our long legs, we strode out
of our continent of origin

and went on to colonise the globe.

But the dexterity of our hands
enabled us to make tools

and transform our environment.

And I think it's really humbling

to realise
that our greatest achievements,

our most advanced technology,
soaring architecture,

exquisite art and music,

they all depend on an unpredictable
series of anatomical adjustments

that changed our ancestors

into walkers and runners and
sculpted the hand of the tool maker.