There is one thing that everyone on Earth has in common.
We all live, eat and breathe within the human body.
For two years, I have been exploring this unique dwelling place.
I want to show you what I have seen.
To come with me, you'll have to cross the globe,
from Australia,
through Africa,
to America.
You'll have to journey into space,
and into a place as mysterious but much closer to home.
We've developed new techniques to help you get there.
New cameras to show you the way.
And we'll look at familiar things with a fresh eye.
You'll journey with me on the road that your body takes.
Through dangers.
Through miracles.
And through time.
We'll see the human body in all its forms,
fom our beginning
to all our ends.
I'm a doctor and a scientist.
I've spent my working life looking at the human body.
Now I'm going to see it in a new light.
Come with me.
This is Charlotte.
She was born just a few hours ago.
Like most of us at birth, there's really nothing to her.
A bit of fat, a little sugar.
A bit of protein.
She's really just a collection of chemicals.
And yet she's the most complicated thing on Earth.
During her lifetime, she'll achieve the most amazing things.
She'll eat for nearly three and a half years,
consuming 7,300 eggs
and 160 kg of chocolate.
She'll produce 40,000 litres of urine and spend over six months on the loo.
She'll dribble 145 litres of saliva before her first birthday.
She'll crawl 150 km before she's two.
Then she'll learn a new word every two hours for the next 10 years.
By the time she's ten, her heart will have beaten 368 million times.
She'll spend a little over 12 years watching TV.
And two and a half years on the telephone.
She'll spend two weeks kissing.
She'll grow 28 metres of fingernails,
and 950 km of hair on her head...
and more than two metres up her nose.
By the age of twenty one,
she'll have breathed over 31/2 million balloons of air.
She'll work for a total of just over eight years.
She'll produce 200 billion new red blood cells each and every day.
She'll be able to put a name to 2,000 people.
150 of them she'll call her friends.
She'll shed 19 kg of dead skin.
She'll have sex 2,580 times..
with five different people.
She'll fall in love twice.
She'll blink 415 million times.
Her eyes will be able to distinguish over a million colours.
If she gets married, she'll spend £6,809 on her wedding day.
to the same person for the rest of her life.
She'll have two children
and four grandchildren.
When they grow up, only two of her eight great-grandchildren
will remember what her name was.
In Britain, she's likely to live for 79 years;
in France, 82 years; in the USA, 80 years;
and in Africa, only 55 years.
By that time, she'll have walked over 22,000 km
and talked for 12 years.
It's an amazing list.
In fact, no life is an ordinary story.
We will each in our time do an incredible amount.
And the driving force behind everything we do
is the most complicated and mysterious organ in our bodies - it's our brain.
This is something I've never done before in my life,
and I never thought I would.
Despite my brief experience, I can do a bit of it on auto-pilot.
A little bit anyway!
(INSTRUCT0R) Braking. Braking.
Braking... No, no!
You were going too fast.
This kind of driving takes a whole new range of skills.
And you need to be able to use them almost automatically.
It's my brain that lets me do that.
My brain is now doing half a dozen tricky new jobs all at once,
without my even thinking about it.
So much so that I can devote some of my attention speaking to you.
(INSTRUCT0R) Lift off. Get your brain into gear!
And that's what brains are so good at.
They manage things without us being conscious of them.
Your brains are doing it right now,
because whilst I've been doing six new things,
your brains have been doing tens of millions of tasks,
just while you're watching television.
Put another way, it's as if you're not just driving this car,
but driving every car, bus, bike, taxi, lorry in the country
at the same time.
And you just thought you were putting your feet up!
To see how busy your brain really is,
you have to look at the world differently.
Everything that's alive, and some things that aren't, gives off heat.
That's what you're looking at now.
All your body is burning up energy and creating heat
as it goes about the business of being you.
But the hottest bit of you is up here.
Your brain burns up the most energy in your body,
almost a fifth of all the calories you consume.
And it uses up almost the same amount
whether you're concentrating on something difficult
or just wondering whether to put the cat out.
Your brain is constantly challenged with its most difficult task:
keeping you alive.
Right now, there are a few things on your mind.
Tonight's dinner, for example.
For starters,
your brain is coordinating a major haulage operation.
Though the route is usually downhill, food doesn't fall to your stomach.
When you swallow, your brain triggers muscle contractions.
They squeeze things along in your oesophagus at 4 cm per second.
The first scheduled stop is the stomach.
It's essentially a biological liquidiser.
Its lining is covered in delicate folds
which allow it to expand with each mouthful.
Inside, a mixture of enzymes and hydrochloric acid
start to digest your food.
Your dinner's probably still inside. It churns away for about four hours.
Soon it will be released into your small intestine,
and, at a cue from your brain, bile will be added.
This will help you break down fats.
You'll be carrying tonight's dinner for about 24 hours.
So I hope you liked it.
When it does leave you,
it will take about 25 grammes of dead cells from your gut with it.
But don't worry.
You're constantly replacing cells from head to toe.
Your brain is managing the body's workforce of 50,000 billion cells.
And most of them don't last more than a few years.
Cells are constantly dying...
and being replaced by new ones,
up to a billion new cells for old every hour.
This means that most of your body is a good deal younger than you are!
But these cells aren't replaced and they're particularly special.
Each one has a natural tendency to twitch.
They're heart cells, and millions working at once is a heartbeat.
It's your head that rules your heart,
as it's your brain that decides what rate your heart should beat at.
The part of the brain controlling your heart
is looking after the outside of you, too.
Your body must maintain a temperature of 37 degrees Centigrade.
And your brain has a range of tricks up its sleeve to do it.
This is skin magnified a thousand times.
If you look closely, it's covered in holes.
They're the openings of tiny ducts,
tubes through which sweat can flow.
There are about 65,000 of them on the palm of your hand alone.
If you're getting too hot, your brain switches on your sweat glands.
As the sweat evaporates, it will help cool you down.
Should your brain decide that warmth is needed, it has another plan.
Goose pimples.
They trap warm air near to the skin and so keep vital heat in.
So, all that is being controlled from here, inside your head.
And don't think you'll get out of all the hard work by nodding off.
Even when we're relaxed or asleep,
our brains don't let up.
This contraption is covered in electrodes,
picking up part of my own brain's activity.
128 sensors detect tiny signals emitted as my brain cells fire.
This is the pattern produced when I am relaxed.
Even without a thought in my head, my brainwaves show I'm busy.
The truth is our bodies are always busy.
They just don't tell us about it.
What we see as the monotony of our daily lives,
when it seems that nothing happens,
is actually the result of much activity inside our bodies.
We're performing thousands of tasks every second of every day.
Simply being is part of a complicated balancing act,
the mechanics of which are completely hidden from us.
Just as our bodies hide the miracle of everyday life,
so they hide from us an even bigger surprise.
It's the story of how we came to be the way we are.
And it is an amazing story.
It will change how you think about your body.
The way we live, the shape we are, even the way we think,
was decided for us thousands, millions, even billions of years ago,
when the human body didn't even exist and planet Earth was unrecognisable.
Here we are, 8,000 feet above sea level
in America's Yellowstone National Park.
If you'd been on the planet 3 billion years ago,
it would have looked something like this.
The Earth was covered in volcanoes, billowing steam and sulphurous water.
Had you been standing here,
you'd have been present as the story of life was unfolding.
Had you been standing here,
you'd have been standing by the planet's most advanced life form.
In this almost boiling water
there are thousands of long, thin strands.
They are colonies of tiny, heat-loving creatures: bacteria.
0nce, long ago, this was the most complex life form on Earth.
What's surprising is it's still here today,
just like 3 billion years ago.
Whilst dinosaurs came and went, and many other species died out,
this has survived practically unchanged.
This is because their environment has stayed the same.
The water comes from deep in the Earth
and so is always the same temperature.
Just metres away, the environment is very different.
Away from the thermal vents, the temperature fluctuates.
Billions of years ago, bacteria were living here, too.
But as the conditions changed, they changed as well.
From one generation to the next, there were alterations.
They were almost insignificant,
but these tiny changes started an amazing process.
Because if you add up enough tiny changes through generations,
you get a revolutionary transformation.
From being simple bacteria, they became more complicated.
Single cells became groups of cells
and then early plants and animals.
And the changes continued.
Dozens of species became hundreds, hundreds into tens of thousands.
Parts of bodies were adapted to meet new challenges.
Great leaps were made.
A fish's fins, over countless generations, developed into legs,
and it became a reptile.
Some reptiles developed feathers and became birds.
0thers became mammals in every shape and size from blue whale to baboon,
every creature we see on the Earth today, including ourselves.
All this happened. It's the miracle of evolution.
The human body is just one branch in the huge, spreading tree of life
that grew from those simple bacteria.
Yet we carry with us the remnants of what has gone before us in our strange past.
And there is a place we can go to see just one of those remnants,
shaped by one of evolution's truly incredible transformations.
It's inside my own head.
All we need to do is go and find it.
This is my ear drum, a thin skin stretched tight across my ear canal.
But what I want to show you lies on the other side of my ear drum.
This device can take me there.
I'm inside a huge magnet with a field strong enough to lift a car clean off the ground.
It's a Magnetic Resonance Scanner
It can reveal layer by layer what's inside my head.
Up until now this has been the forefront of medical imaging.
But we're about to take it one step further.
By putting the medical scans together, we've created a 3-D picture of my own head,
and I can look at any part of it I want to.
I can see the muscles that make up my face.
My skull.
And my own brain.
So now I can take you on that journey into my ear
in a way that's never been possible before.
This time we can fly straight through my ear drum.
We're inside my head and at last I can show you what we've come here to see.
0n the right it's my ear drum again.
But now we're looking at it from the back.
Attached to the middle of it is what I want to show you.
It's a bone.
Though it's towering above us, it's actually tiny,
about the size of a grain of rice.
It's the first in a chain of three bones
which transfer the vibrations of my ear drum
to receptors in my cochlea.
They are the smallest bones in my body
and they're perfectly engineered to perform their task.
Yet these bones will reveal how evolution has transformed us,
because they were once something completely different.
Let me take you back, even before birth,
and the bones will tell us their story.
A foetus in the womb, just twelve weeks old,
and it's only a few centimetres long.
It would fit in an eggcup.
Deep inside its head, its ear bones are forming.
Now let's look at younger and younger foetuses.
Eight weeks.
Seven weeks.
Six weeks.
We are actually witnessing something amazing,
because at certain times in this early development,
our human embryo portrays the shapes of the embryos
of some of our distant pre-human ancestors.
In other words, what we're looking at now is like the embryo of a creature
which we evolved from millions of years ago.
It's just as if we are journeying back in time,
virtually rewinding evolution to show episodes in the history of life.
If we use the magnetic scanner,
incredible detail is revealed.
We can see right through the skin at the brain and the spinal chord beginning to form.
And the beginnings of an eye behind the emerging hand.
Like some of the creatures that preceded us on the evolutionary tree,
it has a curved spine
and what might be a tail.
And those amazing ear bones we saw earlier are taking shape on the outside of the head.
The cells that will make them are located here -
tiny grooves almost hidden behind that hand.
Millions of years ago,
the embryo of a distant ancestor of ours would have shared with us many of these features.
As well as giving rise to us,
it gave rise to all sorts of other creatures.
In those creatures,
these features that we're looking at here have evolved quite differently.
We can actually see it happening with the ear bones,
because those very same grooves that in us will become our ear bones
in this creature become something else entirely.
This is the embryo of a fish.
Here is its heart and it, too, has a curved spine.
And the tiny grooves here, just a fraction of a millimetre long,
have evolved to become not ear bones but supports for its gills.
So, some time long, long ago,
this lot and I shared a common ancestor.
And like them, it, too, had little bones around its gills which helped it to breathe.
But as we evolved,
these little bones were adapted for an entirely different job:
to become the intricate mechanism of our ears.
And our ear bones are not the only things to have been transformed in this way.
Such apparent miracles are in fact all around us.
The rest of our ears, that allow us to balance and walk upright as well as hear,
our limbs and hands, our whole body has been shaped by the process of evolution.
Everything about the human body has been inherited and adapted
from something our ancestors had a long time ago,
though they may have used it for something different.
We are recycled from the past.
0nce we begin to understand the source from which our bodies are derived,
the way we look at ourselves can never be quite the same again.
So every part of the human body bears a shadow from our distant past.
Evolution has adapted our bodies from those of our ancestors,
all the way back since life was as simple as that in the steaming pools of 3 billion years ago.
It is incredible, and it's incredibly hard to believe, too,
because although we've changed so much,
we don't actually see any of those changes happening.
Generation after generation, we just look the same.
The problem is one of time.
The periods over which even tiny changes happen are so long
they're almost beyond our imagination.
But to make sense of those time periods and to see them in perspective,
I've brought you here, to a cave deep in the French Pyrenees.
In the middle of the last century,
a bookseller from the nearby town of Toulouse used to visit this cave,
and as a hobby he dug around for bones and evidence of prehistoric remains.
And he did this for some forty years.
And then, late in the afternoon, on June 11th, 1905,
having been digging all day, he prepared to go but chose to go by a different route.
As he left, he was passing this wall and something caught his eye.
He lifted up his lamp and this is what he saw.
Stencils of human hands from merely 30,000 years ago.
They are amongst the oldest images made by human beings on the planet.
They are six times older than the pyramids in Egypt
and eight times older than Stonehenge.
Quite what they signified to the people who made them, no one knows.
They were a Stone Age people,
and they came here at the coldest part of the last Ice Age.
And over here are the most interesting images of all.
It is thought that these stencils here were made by someone no bigger than a toddler:
a child in a primitive world,
the son or daughter of somebody who we would think of as a caveman.
And yet if I had taken such a child and brought it up as a baby in my own house,
it would be indistinguishable from my own children.
Because by the time these people pressed their hands against these walls,
all the changes which make us what we are had already happened.
The evolution of the human body was, to all intents and purposes, complete.
If this child were to be raised with my own children,
it would look the same, it would talk the same,
it would play the same computer games,
and it would grow up wanting to be a doctor,
a footballer or maybe even an astronaut.
What amazes me more is that,
although we've changed so little in so many thousands of years,
each of us changes so much in just one lifetime.
We tend to think of growing up as just getting older and bigger.
But as we make our way through life,
our bodies change much more significantly than we realise.
In fact, we change just as dramatically as a caterpillar.
A caterpillar is an eating machine
and that's just what it needs to be, to stockpile the energy it will need to reproduce.
Yet, to meet a suitable mate, it may have to travel many miles
and it's hardly equipped for that!
But evolution has provided the caterpillar with a solution.
0ne creature is recycled into another.
A new challenge has been met with a new answer.
0ur bodies, too, face different challenges in life and we are reworked to cope with each of them.
From the moment we are born, we are changing...
and adapting to life's demands.
And every change we make follows a plan drawn up for us
by the millions of generations that have gone before.
In this series, I'm going to show you the science of these changes throughout life.
How our brain cells are wired up when we are children.
How hormones transform us at puberty.
What changes happen inside our bodies.
How our muscles become stronger.
How our brains mature as adults.
And how our bodies continue to alter throughout our lives.
But if I were to tell you just the science of these changes,
I'd be missing the most important thing of all.
Let me show you what I mean.
This is the amount of tears that an average person cries during a lifetime.
Just a fraction under sixty-five litres.
0r, to put it another way,
about one million, eight hundred and fifty thousand drops.
So what do we know about them?
Well, each tear weighs 35 thousandths of a gramme
and is about as salty as this part of the River Thames at Greenwich.
Tears are produced by a gland above the eye which is literally squeezed when we cry,
and the tears come down six tiny tubes about the thinness of a human hair.
As far as we can tell, of all the animals in the world
only humans actually cry when we're hurt or upset.
About twenty-eight drops each time.
including sugar and antiseptics.
But what's the most important thing to know if all these were your tears?
0f course, it's why you cried them.
How many of these thousands of droplets were shed in fits of anger?
How many in pain?
How many in love? In grief?
How many in sorrow? How many were shed by a baby?
And how many by an old man facing the end of life?
The truth is a knowledge of the science of life is only made complete
by a knowledge of those living it.
The human body is not just a biological machine,
it's much more than that - it's a person.
In this series, it's people that will tell us what the body's ever-changing story means.
Take Zak, for example. Having already mastered the complexities of crawling,
he'll be taking his first steps.
When it comes to growing up, 12-year-old Beatrice will ride the rollercoaster of puberty.
(BEATRICE) When you're a teenager, apparently you go bolshie.
You get your periods, you get pubic hair,
you get taller, you get...sort of... wider at the hips, I think. I can't remember.
(BEATRICE) It's painful to run, I can tell you that,
because what happens up above, you have to start wearing a bra. Sorry, had to mention it!
It gets really painful to run.
Month by month, Jeff and Phillippa will share with us perhaps the body's greatest miracle.
(PHILLIPPA) I marvel at the fact that this is going on with no intervention from me.
It's just my body taking over and doing it all.
And I'm not in control of it at all really.
It just all happens.
In adulthood, we reach the peak of human achievement.
Marcia, an astronaut, has scaled the heights.
(MARCIA) There is nothing in our experience,
genetic, metaphysical, emotional,
psychological experience, that prepares us for being off the planet.
(MARCIA) You can look at all of the pictures from space,
and there is something about looking out the window that is not describable.
And we'll be living through the ravages of ageing with 76-year-old Bud and his wife Viola.
They live and work on a farm in the mid-west of America.
What I remember about Bud, he had the prettiest, waviest hair.
- That's different now. - Yes, it is!
And his skin was smooth, no wrinkles.
And he didn't have a little pot here.
And in our last chapter, as his body slowly succumbs to cancer,
Herbie will take us on his final journey.
(HERBIE) I know I'll never see this film in my lifetime.
I like this because everybody sees that a human can manage an illness like mine.
Everybody can see in this film
there is a way to make the best from the end of your life.
So this is the story of the human body,
a tale of fantastic changes and amazing achievements,
written over millions of years of evolution
and told afresh by each of us during our lifetime.
It surely is the greatest story ever told.
And every one of us has a part in it.
From new-born baby upwards,
this line follows the journey we will all make through life.
Each person is one year older than the last.
All of us have a place somewhere along this line,
looking forward, looking back,
or perhaps a bit of both.
Seen like this, stripped of the trappings of wealth and status,
we have one thing in common,
the one place we all inhabit, the one vehicle we all travel in:
it's the human body.
Seeing your body in ways you've never seen before,
perhaps you'll share my sense of wonder at how it shapes us all into who we are.