0:00:03 > 0:00:06There are some great questions
0:00:06 > 0:00:11that have intrigued and haunted us since the dawn of humanity.
0:00:12 > 0:00:15What is out there?
0:00:18 > 0:00:21How did we get here?
0:00:24 > 0:00:27What is the world made of?
0:00:30 > 0:00:34The story of our search to answer those questions
0:00:34 > 0:00:36is the story of science.
0:00:37 > 0:00:39Of all human endeavours,
0:00:39 > 0:00:42science has had the greatest impact on our lives,
0:00:42 > 0:00:46on how we see the world, on how we see ourselves.
0:00:46 > 0:00:52Its ideas, its achievements, its results are all around us.
0:00:52 > 0:00:58So how did we arrive at the modern world?
0:00:59 > 0:01:04The answer is more surprising and more human than you might think.
0:01:07 > 0:01:10It is a tale of power,
0:01:10 > 0:01:13proof,
0:01:13 > 0:01:15and passion.
0:01:23 > 0:01:29This time, one of the more intimate questions we've ever asked.
0:01:29 > 0:01:32What makes us human?
0:01:54 > 0:01:56The question, what is human nature,
0:01:56 > 0:02:00what is it that shapes our thoughts, feelings and desires,
0:02:00 > 0:02:06is one that philosophers, writers and religious leaders have all struggled with.
0:02:06 > 0:02:12I am particularly interested in how science has wrestled with this particular question,
0:02:12 > 0:02:15and that's not just because it gets to the heart of who we are,
0:02:15 > 0:02:20but also because it gets to the heart of what science itself is.
0:02:25 > 0:02:31I want to begin with one of the great civilisations of the ancient world -
0:02:31 > 0:02:33Egypt.
0:02:36 > 0:02:40The ancient Egyptians were amongst the first people we know about
0:02:40 > 0:02:45to really wrestle with the question, what makes us human?
0:02:49 > 0:02:52We humans are acutely aware of ourselves,
0:02:52 > 0:02:56of the sense of being alive, of living within our own skin.
0:02:56 > 0:03:00But where does this "me" reside?
0:03:00 > 0:03:03Where is the control centre?
0:03:03 > 0:03:07Where is the essence of what I truly am?
0:03:09 > 0:03:12Egyptian beliefs about what made us human
0:03:12 > 0:03:16are revealed in their attitudes to the afterlife.
0:03:18 > 0:03:21Certain organs, like the stomach, lungs or liver,
0:03:21 > 0:03:26were seen as so critical they were frequently removed, embalmed,
0:03:26 > 0:03:31and put back inside the body for burial.
0:03:33 > 0:03:37The Egyptians believed that the heart was the key to the afterlife,
0:03:37 > 0:03:42that when you died it would testify for your good or your bad deeds.
0:03:42 > 0:03:46On this papyrus you can see a heart being weighed up against a feather.
0:03:46 > 0:03:50If it was heavier than the feather then this demon over here
0:03:50 > 0:03:52would come and eat it, and that was all over for you.
0:03:52 > 0:03:59In fact, the idea of being light-hearted or heavy-hearted comes from the Egyptians.
0:03:59 > 0:04:04And in a way you can understand why they thought that the emotions resided in the heart.
0:04:04 > 0:04:09Certainly when I have been broken-hearted I've felt it in my gut, and in my chest.
0:04:11 > 0:04:16So the Egyptians treated the heart with great reverence.
0:04:16 > 0:04:21But what about that other organ we now regard as more central to our humanity?
0:04:26 > 0:04:29Here at Manchester University,
0:04:29 > 0:04:35a team of Egyptologists are studying a 2,500-year-old mummy.
0:04:35 > 0:04:39An endoscope is going to be pushed up its nose
0:04:39 > 0:04:43to show me how the Egyptians treated the brain.
0:04:45 > 0:04:48Carefully.
0:04:49 > 0:04:52As we enter the nose
0:04:52 > 0:04:54through the nasal septum...
0:04:54 > 0:04:57How extraordinary.
0:04:59 > 0:05:02- It's like going into some sort of hidden cave.- It is, isn't it?
0:05:02 > 0:05:04It's a secret world, really.
0:05:05 > 0:05:09We would normally be stopped from going through there because of the bone
0:05:09 > 0:05:12that would separate the brain from the nasal cavity.
0:05:12 > 0:05:16- Which should be there. - Yes, it should be there, of course.
0:05:16 > 0:05:19- Right. And so now you're actually entering the skull?- Yes.
0:05:23 > 0:05:25Ooh!
0:05:25 > 0:05:28That's a sort of, a suture in the top of the head, isn't it?
0:05:28 > 0:05:32There seems to be something missing.
0:05:32 > 0:05:35Yes, there's a brain missing.
0:05:35 > 0:05:37How extraordinary.
0:05:37 > 0:05:40Do they not see the brain as important?
0:05:40 > 0:05:44They recognised that the brain controlled some of the bodily actions,
0:05:44 > 0:05:49but they certainly didn't think that the individual personality
0:05:49 > 0:05:51was located in the brain.
0:05:51 > 0:05:53So they removed it and discarded it.
0:05:53 > 0:05:56- So they just took it and chucked it out.- Yes.
0:05:56 > 0:06:02- It shows a certain contempt for what we regard as one of our more important organs now.- Absolutely.
0:06:04 > 0:06:10The Egyptian concept of what makes us who we are was a mystical union
0:06:10 > 0:06:15between the physical body and an everlasting spirit.
0:06:19 > 0:06:25One of the recurring ideas to emerge out of early civilisations like the Egyptians
0:06:25 > 0:06:29was the belief that we are more than simply flesh and blood.
0:06:29 > 0:06:34There is something else, something which is special and makes us human.
0:06:34 > 0:06:40This conviction is one of the most powerful and enduring in human history.
0:06:44 > 0:06:48This belief shapes thinking for millennia.
0:06:50 > 0:06:53But as Europe emerged from the Middle Ages,
0:06:53 > 0:06:56people started to approach the question differently.
0:06:59 > 0:07:03The physical and intellectual frontiers of Europe were changing,
0:07:03 > 0:07:08and that would encourage a very different view of who we are.
0:07:16 > 0:07:22That new view can be glimpsed here, the grandest royal palace in France.
0:07:29 > 0:07:34Amongst this great splendour, there's an intriguing technology...
0:07:35 > 0:07:41..that to me reflects a great change in how we saw ourselves,
0:07:41 > 0:07:44captured in one magnificent room.
0:07:53 > 0:07:57And this is it. It's the great hall of mirrors in Versailles.
0:08:02 > 0:08:06It is absolutely fantastic,
0:08:08 > 0:08:12and the whole room utterly dominated by this wall of mirrors
0:08:12 > 0:08:14which extends down almost 100 metres.
0:08:14 > 0:08:17I've never seen mirrors on this scale.
0:08:36 > 0:08:40This really is cutting-edge technology.
0:08:40 > 0:08:44Now this is not absolutely perfect, the surface not completely smooth,
0:08:44 > 0:08:47you can see little bubbles here in the glass.
0:08:47 > 0:08:51It's not perfect, it's not like a sort of modern mirror.
0:08:51 > 0:08:54But the size and the scale is unlike anything
0:08:54 > 0:08:56which was really done before,
0:08:56 > 0:08:59and compared to the sort of curvy-wurvy things
0:08:59 > 0:09:02that most people would know of from centuries earlier,
0:09:02 > 0:09:05this was something different.
0:09:05 > 0:09:10Because there was nothing, nothing, nothing like this had been developed before.
0:09:10 > 0:09:13It allowed people to just stand there
0:09:13 > 0:09:16and look at themselves and think, you know, "Who am I?" "This is me."
0:09:18 > 0:09:22These mirrors represent the culmination of an idea
0:09:22 > 0:09:25that had been emerging in Europe since the Renaissance.
0:09:28 > 0:09:32The notion that we are all individuals.
0:09:32 > 0:09:35Not members of a class, or a guild,
0:09:35 > 0:09:41but defined by our own desires, ambitions, and destinies.
0:09:44 > 0:09:49Along with this growing awareness of self came different questions.
0:09:49 > 0:09:52What makes ME who I am?
0:09:52 > 0:09:58Why do I have these hopes, these fears, these talents, these expectations?
0:09:58 > 0:10:03And most importantly of all, what is this "I" anyway?
0:10:12 > 0:10:19Throughout history, the technology of the age has stimulated new ways of looking at the world.
0:10:21 > 0:10:23I can see a thing which looks a little bit...
0:10:23 > 0:10:26I don't know what it is, it looks like some sort of sea creature, possibly a prawn.
0:10:28 > 0:10:35New inventions have created metaphors to help us think about what makes us human.
0:10:36 > 0:10:40This makes me smile.
0:10:41 > 0:10:45In 17th-century France, the philosopher Rene Descartes
0:10:45 > 0:10:48was wrestling with the question of human nature.
0:10:50 > 0:10:55For inspiration, he drew on a technological wonder of the age -
0:10:55 > 0:10:58water-powered mechanical statues.
0:11:04 > 0:11:09The story goes that Descartes is wandering through the royal gardens
0:11:09 > 0:11:15and he sees a fountain, and in the middle of the fountain there is an enormous statue of Neptune,
0:11:15 > 0:11:17which is spouting water, a bit like this.
0:11:17 > 0:11:22And this particular Neptune, when you come close, sort of starts to jab at you with the trident.
0:11:22 > 0:11:26And Descartes is rather taken by this, and he starts to think,
0:11:26 > 0:11:33and he thinks perhaps animals are just a form of automata,
0:11:33 > 0:11:36that perhaps a prawn really has some sort of gears in it
0:11:36 > 0:11:39with lots of sort of intersecting bits and pieces.
0:11:39 > 0:11:43And then he starts wondering, perhaps that's what our bodies are,
0:11:43 > 0:11:47they're just sophisticated machines.
0:11:48 > 0:11:52For the time this was a very daring idea,
0:11:52 > 0:11:55to suggest we are like machines,
0:11:55 > 0:12:01but it begged the question, what special quality actually makes us human?
0:12:05 > 0:12:09Descartes was a man desperate for certainty,
0:12:09 > 0:12:11but this was no time to find it.
0:12:16 > 0:12:2117th-century Europe was riven by religious and political conflict.
0:12:24 > 0:12:28Old certainties of Church and State were crumbling.
0:12:28 > 0:12:32What, thought Descartes, could he trust?
0:12:32 > 0:12:36What could he really know?
0:12:38 > 0:12:40Descartes is wracked by doubts,
0:12:40 > 0:12:43and he wants to find out something he can believe in.
0:12:43 > 0:12:47Imagine, says Descartes, a tower,
0:12:47 > 0:12:51and the tower is in fact round, but you perceive it as square.
0:12:51 > 0:12:54Or, for example, this thing here - from a distance it looks square
0:12:54 > 0:12:57but actually when you hold it up it is clearly round.
0:12:57 > 0:12:59Your vision has been deceived.
0:13:01 > 0:13:06And then Descartes wondered if all his senses were deceiving him.
0:13:08 > 0:13:11He could feel the warmth of his fire,
0:13:11 > 0:13:15see its light, hear its sound,
0:13:15 > 0:13:20but he'd experienced the same sensations in a dream.
0:13:21 > 0:13:26So perhaps the whole world he was living in was nothing but an illusion.
0:13:30 > 0:13:34Descartes is now beginning to really question everything -
0:13:34 > 0:13:37the moon, the sky, the stars.
0:13:37 > 0:13:42Perhaps they're all figments of his imagination. But what about maths?
0:13:42 > 0:13:45Two plus three - it always equals five, doesn't it?
0:13:45 > 0:13:49But maybe there's a demon who's taken possession of his brain.
0:13:49 > 0:13:54Descartes is really beginning to doubt everything,
0:13:54 > 0:14:01down to the very question of whether he himself existed at all.
0:14:05 > 0:14:07And then, finally, he got there.
0:14:07 > 0:14:11He realised that the act of doubting implied a doubter.
0:14:11 > 0:14:14There was one thing he could be absolutely certain of -
0:14:14 > 0:14:19the existence of his own thinking, doubting mind.
0:14:19 > 0:14:26He summed it up in a neat philosophical phrase - "I think, therefore I am".
0:14:29 > 0:14:35It may be a familiar phrase, but it contains a profound idea -
0:14:35 > 0:14:39the claim that the essence of our humanity lies in our thoughts,
0:14:39 > 0:14:41our ability to reason.
0:14:41 > 0:14:47And reason was to form the basis of a new, experimental science.
0:14:56 > 0:15:02Across the Channel, a much more bloody approach to the question of "Who are we?"
0:15:02 > 0:15:05was to emerge from a great political clash -
0:15:07 > 0:15:10the English Civil War.
0:15:10 > 0:15:13Oxford was a key Royalist stronghold.
0:15:13 > 0:15:18For some caught up in the action, turmoil spelt opportunity.
0:15:22 > 0:15:26Here in Oxford, a young man called Thomas Willis was part way through
0:15:26 > 0:15:32his medical training, which in those days lasted an incredible 14 years.
0:15:32 > 0:15:35The Civil War interrupted his studies,
0:15:35 > 0:15:37which in many ways was a very good thing.
0:15:40 > 0:15:46Studying medicine didn't necessarily make you a good doctor,
0:15:46 > 0:15:48for one very good reason.
0:15:50 > 0:15:56Medical teaching was still largely based on ideas from antiquity.
0:15:56 > 0:16:03The disruption of his studies gave Willis the opportunity to investigate the body for himself.
0:16:05 > 0:16:10By now, people were exploring the anatomy of the brain.
0:16:10 > 0:16:14But still, no-one really knew what it did.
0:16:17 > 0:16:23In the mid-1600s, Willis began a ground-breaking series of dissections,
0:16:23 > 0:16:28and I'm about to get a privileged glimpse of what he would have seen.
0:16:30 > 0:16:34- Ah!- There we are.- Human brain. Isn't it wonderful?- It is.
0:16:34 > 0:16:42It is utterly unbelievable when you think that this brain once thought, it reasoned.
0:16:42 > 0:16:45It's a unique feature of the universe, really.
0:16:47 > 0:16:50When a brain is sort of fresh it's a very different consistency.
0:16:50 > 0:16:53Yes, it is, it's... I tell students it's a bit like a badly set jelly.
0:16:53 > 0:16:57But presumably if you were to cut that you really would have great difficulties.
0:16:57 > 0:17:00Yes, it would just fall to pieces, really.
0:17:01 > 0:17:05Willis was one of the first o use a new technique -
0:17:07 > 0:17:10preserving brains in alcohol.
0:17:10 > 0:17:14This made them firm enough to dissect with great precision.
0:17:16 > 0:17:18- You ready to cut this? - Yes, ready to cut.
0:17:27 > 0:17:28Isn't it strange?
0:17:32 > 0:17:33Ah!
0:17:33 > 0:17:40What's really curious is that there's almost no structure or definition to it, is there?
0:17:40 > 0:17:44The thing that really catches your eye is the ventricles in the centre,
0:17:44 > 0:17:48which were what everybody was preoccupied with before Willis.
0:17:48 > 0:17:55And the idea was that this part of the brain may have acted as a sort of pump,
0:17:55 > 0:18:01and important activities may have gone on in the fluid that was moving around in the ventricles.
0:18:01 > 0:18:04So in a sense all this is just muscle, and all the thought
0:18:04 > 0:18:07and the important stuff is taking place in these holes over here?
0:18:07 > 0:18:09Yes, and it was Thomas Willis who realised that
0:18:09 > 0:18:13the actual structure of the brain was what was critically important.
0:18:14 > 0:18:19When Willis looked at animal brains, he concluded our intellect
0:18:19 > 0:18:25and thoughts must lie in the parts of the brain animals don't possess.
0:18:25 > 0:18:30Thomas Willis was very struck by the corrugated surface of the human brain
0:18:30 > 0:18:33as compared to the smooth surface of the sheep, and this enables
0:18:33 > 0:18:37a huge volume of cerebral cortex to be contained
0:18:37 > 0:18:40within the relatively small volume of the skull.
0:18:40 > 0:18:43- And that's where he thought being human resided?- Yes.
0:18:43 > 0:18:47You can see there's a ribbon of cortex going over the surface
0:18:47 > 0:18:51- of the cerebral hemispheres. - Oh, just there.- Yes, that's right.
0:18:51 > 0:18:57And this cortex was where he realised people were likely to have their thoughts.
0:19:00 > 0:19:05Willis had established a link between the state of the brain and the state of the mind.
0:19:07 > 0:19:12He wrote the first book specifically about the brain.
0:19:12 > 0:19:16From now on, anatomical studies would become
0:19:16 > 0:19:22one of the great foundations of a scientific explanation of who we are.
0:19:32 > 0:19:36Reason was now seen as the pinnacle of human nature.
0:19:36 > 0:19:40It had been shaped by philosophical doubt,
0:19:40 > 0:19:43and detailed dissections of the brain.
0:19:45 > 0:19:50Europe entered a new age, a celebration of the rational mind.
0:19:53 > 0:19:57Faith in reason would underpin the growth of trade
0:19:57 > 0:20:00and the building of empires.
0:20:08 > 0:20:14In 1837, something was causing a stir at London Zoo.
0:20:16 > 0:20:19Their first orang-utan, Jenny,
0:20:19 > 0:20:22was introduced to an astonished audience.
0:20:24 > 0:20:29Exotic animals were being brought to Britain from across the Empire.
0:20:34 > 0:20:38Even Queen Victoria herself came calling.
0:20:42 > 0:20:48Jenny's arrival would challenge assumptions about what makes us human.
0:20:48 > 0:20:52Right, come this way, Michael, I'll introduce you to Batu,
0:20:52 > 0:20:55who should be waiting. There he is.
0:20:55 > 0:20:59- There he is. Hello.- This is Batu. - Wow, he's big.
0:20:59 > 0:21:01- Hello.- Batu's very big.
0:21:01 > 0:21:04- What a beautiful face. - Very big and very strong.
0:21:04 > 0:21:07- Right. Can I do this?- Yeah, just be careful with the orange.
0:21:07 > 0:21:09Yeah.
0:21:09 > 0:21:12Oop, very delicately done!
0:21:12 > 0:21:13He doesn't want to drop it.
0:21:15 > 0:21:18He's even ruder than my kids!
0:21:20 > 0:21:21That's rude, stop it.
0:21:21 > 0:21:24You could actually see a wonderfully sort of sullen look on his face.
0:21:24 > 0:21:27- Yeah. - That look of "Mm, don't like that."
0:21:27 > 0:21:29It's a very human expression.
0:21:31 > 0:21:35Odd behaviour. Oh, no, that's terrible!
0:21:35 > 0:21:37Ah! Ugh!
0:21:37 > 0:21:42It's wonderful, this is a, a great sense of independence.
0:21:42 > 0:21:44Stop it now.
0:21:44 > 0:21:46You've spat at me.
0:21:46 > 0:21:48You've played your game.
0:21:48 > 0:21:50What are you going to do next?
0:21:52 > 0:21:54Oh, that's smelly!
0:22:00 > 0:22:05One of the visitors to the zoo was young Charles Darwin.
0:22:06 > 0:22:09But this isn't the familiar story about evolution.
0:22:12 > 0:22:16His visit to the zoo was part of his lesser-known research -
0:22:19 > 0:22:22fascination with animal emotion.
0:22:24 > 0:22:28One day, Darwin saw something that really astonished him.
0:22:30 > 0:22:35Jenny was playing with the keeper, and the keeper had an apple,
0:22:35 > 0:22:41and the keeper was taunting Jenny by waving the apple in front of her but not letting her get hold of it.
0:22:41 > 0:22:47And in Darwin's words, "The ape threw herself on her back and cried precisely like a little child."
0:22:52 > 0:22:56Darwin became convinced that the expressions of emotion
0:22:56 > 0:23:01he saw in Jenny and in humans were the same.
0:23:01 > 0:23:04His research developed over 30 years.
0:23:07 > 0:23:11Tenderness, shame, joy -
0:23:11 > 0:23:14he saw them all in animals.
0:23:18 > 0:23:22Darwin's painstaking work led to one of his most important books,
0:23:22 > 0:23:28The Expression Of The Emotions In Man And Animals.
0:23:28 > 0:23:32It was greeted with alarm and fascination.
0:23:32 > 0:23:35Now this is a really incredible book,
0:23:35 > 0:23:40partly because of the illustrations, because this is one of the first books ever to include photographs.
0:23:40 > 0:23:45And they feature people, people in various states of distress, if you like.
0:23:45 > 0:23:49Disconsolate, sad, very sad-looking.
0:23:49 > 0:23:51He examines it in almost microscopic detail.
0:23:51 > 0:23:56There's a very interesting picture here of a woman's forehead,
0:23:56 > 0:23:58and he notices these two lines coming up here,
0:23:58 > 0:24:02which were later called in fact the Darwin grief muscle.
0:24:04 > 0:24:10What Darwin was undermining in his work was a fundamental belief -
0:24:11 > 0:24:15a belief in human uniqueness.
0:24:24 > 0:24:27By suggesting a close kinship with animals,
0:24:27 > 0:24:30he'd also opened the lid on the rational mind,
0:24:30 > 0:24:37hinting at a dark subterranean world of instincts, desires, emotions -
0:24:37 > 0:24:38the animal within.
0:24:43 > 0:24:47Here was an irony for Victorian science.
0:24:47 > 0:24:51The power of reason, which made us unique,
0:24:51 > 0:24:54had been turned on ourselves,
0:24:54 > 0:24:58and revealed us to be less exalted, less rational,
0:24:58 > 0:25:00than had been suspected.
0:25:09 > 0:25:14A new side of ourselves was being unearthed,
0:25:14 > 0:25:18darker and more dangerous.
0:25:21 > 0:25:27In Paris, doctors began to explore this untamed side,
0:25:29 > 0:25:31at La Salpetriere.
0:25:33 > 0:25:38This imposing-looking building was originally used to store gunpowder,
0:25:38 > 0:25:41but then they decided they could put it to better use,
0:25:41 > 0:25:45to lock away thousands of people who were regarded as just as
0:25:45 > 0:25:49unstable and dangerous - the destitute and the insane.
0:25:55 > 0:26:00It had been Europe's most notorious women's asylum,
0:26:00 > 0:26:04with nothing to offer but cruel imprisonment.
0:26:07 > 0:26:11These are some of the cells where they kept the women,
0:26:11 > 0:26:16and these are the original bars behind which they were imprisoned.
0:26:16 > 0:26:23And there is something terribly poignant about the idea of thousands of women chained up,
0:26:23 > 0:26:26in filthy living conditions,
0:26:26 > 0:26:33utterly without any prospect of release, no hope, no hope at all.
0:26:37 > 0:26:40But attitudes were changing.
0:26:40 > 0:26:45After years of revolution, the asylum had become a place of care
0:26:45 > 0:26:48rather than simply imprisonment.
0:26:51 > 0:26:56One of its most famous physicians was Jean-Martin Charcot.
0:26:58 > 0:27:04Often the best way to understand the normal is to study the abnormal,
0:27:04 > 0:27:10and here there were 5,000 troubled minds to study.
0:27:12 > 0:27:16Charcot was one of the first people to try and separate out
0:27:16 > 0:27:20and categorise different forms of mental and neurological illness.
0:27:20 > 0:27:26He took incredibly detailed notes, and he also took lots of photographs.
0:27:28 > 0:27:32One condition in particular had been puzzling doctors.
0:27:34 > 0:27:38They called it hysteria.
0:27:38 > 0:27:44Patients suffered paralysis, seizures, blindness, and violent fits.
0:27:44 > 0:27:49Charcot presumed these symptoms were caused by a physical disease,
0:27:49 > 0:27:57but then he began to use a remarkable new approach.
0:27:57 > 0:28:00Five, six...
0:28:00 > 0:28:01Hypnosis.
0:28:01 > 0:28:04..Seven...
0:28:04 > 0:28:07Charcot found he could induce and relieve
0:28:07 > 0:28:10symptoms of hysteria using hypnosis.
0:28:10 > 0:28:13And become aware of any feelings of lightness, going up.
0:28:13 > 0:28:18It could produce extraordinary effects in the body.
0:28:18 > 0:28:24Drifting up and up now, and the balloon really sort of taking off now and bobbing from side to side.
0:28:24 > 0:28:27OK, can you see the balloon?
0:28:27 > 0:28:29I can, it's a big blue balloon.
0:28:29 > 0:28:32- OK, and it's...- A sort of Winnie the Pooh blue balloon.
0:28:32 > 0:28:34OK. Well, you get that feeling of the...
0:28:34 > 0:28:41'I've tried hypnosis before, but this is the first time it's really worked.'
0:28:41 > 0:28:44OK and just notice what's happening there.
0:28:44 > 0:28:48'Over the course of an hour, I mysteriously lost co-ordination of my hand.'
0:28:48 > 0:28:53And that's even more noticeable in fact, it's becoming really shaky now.
0:28:53 > 0:28:57'I had my hands stuck together.'
0:28:57 > 0:28:58Knuckles are quite locked.
0:28:58 > 0:29:00- Oh!- They are quite locked.
0:29:00 > 0:29:06'And most bizarre at all, one side of my visual field was rendered almost useless.'
0:29:06 > 0:29:09- Seems a bit fainter.- OK.
0:29:09 > 0:29:12And, um, I have a sense of something in there but not really.
0:29:12 > 0:29:15- OK.- Not really objects.- OK.
0:29:15 > 0:29:18One, two...
0:29:18 > 0:29:20'That was extremely odd.'
0:29:20 > 0:29:24It was a bit like I was there but I wasn't there,
0:29:24 > 0:29:27that he was talking to some other part of me,
0:29:27 > 0:29:30and the other part of me was responding.
0:29:30 > 0:29:35- Higher, and higher. - And the idea you can just do it with the power of words...
0:29:35 > 0:29:38quite strange.
0:29:40 > 0:29:43Charcot's observations of hysteria led him towards
0:29:43 > 0:29:45a radical conclusion.
0:29:49 > 0:29:53If symptoms could be induced or relieved by hypnosis,
0:29:53 > 0:29:57then perhaps they were not signs of some pathological disease.
0:29:57 > 0:30:00Perhaps they were caused by emotions,
0:30:00 > 0:30:04that the patients themselves were not even aware they were feeling.
0:30:04 > 0:30:07Charcot never fully grasped what he was dealing with,
0:30:07 > 0:30:11what we would now call the unconscious mind.
0:30:14 > 0:30:18In amongst the crowds at one of Charcot's famous demonstrations
0:30:18 > 0:30:22was a young Austrian doctor, Sigmund Freud,
0:30:24 > 0:30:29a man who would famously use the study of hidden emotions
0:30:29 > 0:30:33and repressed urges to develop this extraordinary concept
0:30:33 > 0:30:35of the unconscious mind.
0:30:37 > 0:30:42Freud's ideas would become a significant cultural influence
0:30:42 > 0:30:43on the 20th century.
0:30:47 > 0:30:51They would join a rising tide of other ideas
0:30:51 > 0:30:57that would form a wholly new approach to who we are - psychology.
0:31:06 > 0:31:09A less than rational self had been revealed -
0:31:12 > 0:31:15by animals brought back from distant lands,
0:31:18 > 0:31:21by changing attitudes to mental illness,
0:31:21 > 0:31:25and a new door into the unconscious mind.
0:31:26 > 0:31:31We could no longer see ourselves simply as creatures of reason.
0:31:42 > 0:31:44By the end of the 19th century,
0:31:44 > 0:31:48Europe was in the throes of a bold new age of communication.
0:31:57 > 0:32:04Thousands of miles of new railway linked the continent's great cities.
0:32:04 > 0:32:07Telegraph cables joined people across the globe.
0:32:13 > 0:32:16This interconnected world
0:32:16 > 0:32:23led to a different way of looking at how the brain works.
0:32:23 > 0:32:26This new technology, naturally enough,
0:32:26 > 0:32:30inspired new metaphors to describe the nervous system.
0:32:30 > 0:32:34For example, if I pinch my finger, then the pain fibres go
0:32:34 > 0:32:38down the line, up into my spinal cord and from there to the brain.
0:32:38 > 0:32:41The thing is, what happens next?
0:32:41 > 0:32:45Well, everyone knew there were complicated signal boxes and junctions up there,
0:32:45 > 0:32:48but nobody knew just how they worked.
0:32:56 > 0:32:58The Spanish countryside.
0:33:03 > 0:33:06Home to a scientist I deeply admire.
0:33:07 > 0:33:13He had a passion for art that would shape his future career as a neuroscientist.
0:33:18 > 0:33:23His name was Santiago Ramon y Cajal.
0:33:27 > 0:33:31When he was a young man, Cajal was obsessed by art.
0:33:31 > 0:33:36As he later wrote, "I was gripped by an irresistible mania.
0:33:36 > 0:33:43"I painted everything that captivated my sight - earth, foliage, plants, the human form".
0:33:43 > 0:33:47He was actually extremely good at putting down on paper what he saw.
0:33:49 > 0:33:51Cajal's passion for art
0:33:51 > 0:33:57was coupled with a fascination for a new technology - photography.
0:33:57 > 0:34:01This is the sort of camera that Cajal would have used.
0:34:01 > 0:34:03I've got it lined up on the mountains now.
0:34:03 > 0:34:07I've got a photographic plate in here,
0:34:07 > 0:34:10which is basically a bit of glass with some photosensitive chemicals on.
0:34:10 > 0:34:12And then you lift this.
0:34:12 > 0:34:16And you trigger the shutter.
0:34:16 > 0:34:19It should take about 20 seconds.
0:34:19 > 0:34:21When that's done, this goes down,
0:34:21 > 0:34:24and the glass plate you take away with you
0:34:24 > 0:34:26off to the mysteries of the darkroom.
0:34:32 > 0:34:36It was his twin passions, art and photography, that would shape
0:34:36 > 0:34:41his most important discovery - what it is that makes the brain work.
0:34:45 > 0:34:48To see, observe, and make things visible
0:34:48 > 0:34:52is one of the great challenges of science.
0:34:52 > 0:34:55The challenge for neuroscientists
0:34:55 > 0:34:58was uncovering the fine structure of the brain.
0:35:00 > 0:35:06The task Cajal set himself was to reveal the communication networks
0:35:06 > 0:35:08that exist inside our heads.
0:35:10 > 0:35:15I've come to the Cajal Institute to see how he did it.
0:35:15 > 0:35:20I always feel like I'm getting into surgery again. Great.
0:35:20 > 0:35:23- So...mouse?- Yeah, take the brain.
0:35:23 > 0:35:28'My first job is to chop up a rather slippery mouse brain.'
0:35:28 > 0:35:31Very small. Hey!
0:35:31 > 0:35:34'It's trickier than it looks'.
0:35:34 > 0:35:36There we go.
0:35:36 > 0:35:38- Feels like cutting onions.- Yes!
0:35:38 > 0:35:40I'm good at cutting onions.
0:35:45 > 0:35:48'The search was on for a stain that would make the mysterious
0:35:48 > 0:35:51'structure of the brain visible under the microscope.'
0:35:55 > 0:35:59'Cajal was shown a technique using chemicals from the darkroom,
0:35:59 > 0:36:02'chemicals that could make brain tissue turn black'
0:36:02 > 0:36:07You can see it's a really complicated process,
0:36:07 > 0:36:09lots of different stages.
0:36:11 > 0:36:15Cajal spent nearly 20 years fiddling away,
0:36:15 > 0:36:18doing minor adjustments, just seeking perfection.
0:36:19 > 0:36:25The great debate was whether the brain was just a mesh of fibres,
0:36:25 > 0:36:28or made of distinct individual units.
0:36:36 > 0:36:42Placing stained tissue under the microscope, Cajal became convinced
0:36:42 > 0:36:47that there were individual building blocks in the brain - neurons.
0:36:50 > 0:36:54Now, that is absolutely beautiful.
0:36:57 > 0:36:58That is a neuron.
0:36:58 > 0:37:01That is what they were looking for.
0:37:01 > 0:37:04Now, the signal goes up here into the cell body,
0:37:04 > 0:37:10and then somehow gets distributed by thousands of axons and dendrites,
0:37:10 > 0:37:13which link in with all the other neurons in the brain.
0:37:13 > 0:37:18Now, only about 1 in 40 of the neurons actually get stained,
0:37:18 > 0:37:22and that might sound like a bad thing, but it's actually an incredibly good thing
0:37:22 > 0:37:25because if all the neurons here were stained,
0:37:25 > 0:37:27then this would be a confusing mass.
0:37:27 > 0:37:29You wouldn't be able to make any sense at all.
0:37:30 > 0:37:33But because it's just 1 in 40, you can pick them out.
0:37:40 > 0:37:43You can see Cajal's artistic influence here -
0:37:43 > 0:37:47beautiful drawings of neurons.
0:37:52 > 0:37:55He mapped out groups of neurons,
0:37:55 > 0:37:58and theorised how they might work -
0:37:59 > 0:38:04that nerve impulses travel along them in one direction,
0:38:04 > 0:38:08passing from one cell to the next.
0:38:11 > 0:38:15Many years later, his theories would be confirmed.
0:38:17 > 0:38:22Cajal realised that these neurons are the basic units of the human brain.
0:38:22 > 0:38:25We now know there are at least a hundred billion of them,
0:38:25 > 0:38:29and all these connecting branches, well, there are trillions of connections.
0:38:29 > 0:38:35And somewhere in here, emotion and thought are born.
0:38:35 > 0:38:40Somewhere in here is the answer to what makes a human.
0:38:54 > 0:38:58Half a century later, the world descended into chaos.
0:39:02 > 0:39:07Out of the turmoil of World War II came a secret invention,
0:39:07 > 0:39:10built here at Bletchley Park in rural England.
0:39:13 > 0:39:21Colossus - the most complex machine that had yet been built.
0:39:21 > 0:39:23Designed to crack enemy codes,
0:39:23 > 0:39:28it would also shed light on the question of who we are.
0:39:28 > 0:39:32What was truly astonishing about Colossus
0:39:32 > 0:39:35was the speed at which it could work.
0:39:35 > 0:39:39Enemy messages which had previously taken teams of human code-breakers
0:39:39 > 0:39:44six weeks to crack could now be done by the machine in six hours.
0:39:44 > 0:39:48It must have seemed truly superhuman.
0:39:50 > 0:39:54Here was a machine doing something that till now
0:39:54 > 0:39:59only the intelligent human mind could do, but much faster.
0:40:00 > 0:40:03Once again, the technology of the day
0:40:03 > 0:40:07offered a model for how the brain might work.
0:40:10 > 0:40:13When you think about it, it's a bit like a primitive brain,
0:40:13 > 0:40:16with the valves representing the neurons
0:40:16 > 0:40:20and the wiring representing the connecting axons and dendrites.
0:40:29 > 0:40:32People had begun to theorise that Cajal's neurons
0:40:32 > 0:40:35worked a bit like electronic switches.
0:40:36 > 0:40:41If intelligence could be replicated by the on-off switching of a machine,
0:40:41 > 0:40:46perhaps the reasoning mind wasn't as uniquely human as we thought.
0:40:50 > 0:40:54One of the biggest human brains at Bletchley was Alan Turing,
0:40:54 > 0:40:57often called the father of modern computing.
0:40:57 > 0:41:03In 1950, he thought of an ingenious way of judging whether computers
0:41:03 > 0:41:07show some form of intelligence, by devising a test.
0:41:09 > 0:41:13The Turing test is actually more of a Turing question.
0:41:13 > 0:41:15The question he asked himself was,
0:41:15 > 0:41:19would it be possible to build a computer that was so intelligent
0:41:19 > 0:41:22and so good at having chats with humans
0:41:22 > 0:41:24that you could be chatting to the machine
0:41:24 > 0:41:28and not be aware that you're not actually talking to another person?
0:41:28 > 0:41:33Well, he suggested that by the year 2000, we would have cracked the problem.
0:41:33 > 0:41:36We are well beyond that point. Let's see.
0:41:37 > 0:41:41Right, "what is your name?"
0:41:41 > 0:41:45You don't remember? No, I don't remember.
0:41:45 > 0:41:50'I'm plugged into one of the more sophisticated programs,
0:41:50 > 0:41:54'designed to respond to Turing's challenge.'
0:41:54 > 0:41:56OK, let's try some, er, general knowledge.
0:41:56 > 0:41:59I mean, computers should be able to do general knowledge.
0:41:59 > 0:42:04'It doesn't ever seem to really answer the question.'
0:42:04 > 0:42:06Anyway, this is garbage.
0:42:06 > 0:42:10'Let's try a different tack - favourite films.'
0:42:10 > 0:42:13Transformers 2.
0:42:13 > 0:42:15Maybe that is some sort of computer joke.
0:42:15 > 0:42:18I can't believe anybody liked Transformers 2.
0:42:18 > 0:42:23"What films make you cry?"
0:42:26 > 0:42:29"Science fiction and comedy. What do you like?"
0:42:29 > 0:42:31Right. It's not very impressive.
0:42:31 > 0:42:35I'm not enjoying myself. I'm not having a great conversation here.
0:42:37 > 0:42:41I think what you can learn from this is that computers are good at computing,
0:42:41 > 0:42:44basically, crunching numbers and things like that.
0:42:44 > 0:42:47What they clearly lack is the thing that
0:42:47 > 0:42:52really gives any form of human interchange any worth, any value -
0:42:52 > 0:42:56feelings like humour, warmth, love, affection,
0:42:56 > 0:43:00any of the things that we actually value.
0:43:00 > 0:43:04Perhaps too much to expect from a machine.
0:43:04 > 0:43:08- Bye bye. - ELECTRONIC VOICE: Goodbye. Goodbye.
0:43:11 > 0:43:16For centuries, technology has provided metaphors to explain who we are.
0:43:16 > 0:43:20The computer is simply the latest we have seized on.
0:43:20 > 0:43:23But its failings reveal that what makes us human
0:43:23 > 0:43:25lies in something a machine cannot do.
0:43:28 > 0:43:32We are passionate, irrational creatures,
0:43:32 > 0:43:35often driven by forces we do not understand.
0:43:47 > 0:43:51At the turn of the 20th century, a great nation was coming of age.
0:43:57 > 0:44:00The United States.
0:44:12 > 0:44:16The land of the free, personal rights and liberties.
0:44:19 > 0:44:22This was the perfect home for the thriving discipline
0:44:22 > 0:44:29that focused on ourselves as individuals - psychology.
0:44:34 > 0:44:39Psychology, as the name implies, originally started out as
0:44:39 > 0:44:42the study of the psyche, or mind.
0:44:42 > 0:44:45The idea was, you could look into yourself, introspect,
0:44:45 > 0:44:47and learn about human nature that way.
0:44:47 > 0:44:51However, here in America, a small group of psychologists soon decided
0:44:51 > 0:44:54that was nowhere near rigorous or vigorous enough.
0:44:54 > 0:44:59They wanted to turn psychology into a science, so they decided to
0:44:59 > 0:45:04focus on something they really could measure and manipulate - behaviour.
0:45:11 > 0:45:14This approach, called behaviourism,
0:45:14 > 0:45:17was transformed into a systematic science
0:45:17 > 0:45:22by one of the 20th century's most controversial pioneers.
0:45:23 > 0:45:25His name was BF Skinner.
0:45:28 > 0:45:30Skinner was convinced that our behaviour
0:45:30 > 0:45:33is the product of our environment,
0:45:33 > 0:45:35learnt from our experiences.
0:45:40 > 0:45:43Since Skinner thought that environment was all-important,
0:45:43 > 0:45:47I thought it would be quite interesting to have a look at where he worked.
0:45:47 > 0:45:50This is his study. Isn't it wonderful?
0:45:52 > 0:45:58This is completely unchanged from when he died, over 20 years ago.
0:45:58 > 0:46:02He liked music, so he had this adapted
0:46:02 > 0:46:05so that he could just pull that,
0:46:05 > 0:46:08and play his music.
0:46:09 > 0:46:13This is a man who likes to tinker and adjust things.
0:46:15 > 0:46:18This is the bed in which he used to sleep.
0:46:18 > 0:46:22It is absolutely filled with his paraphernalia.
0:46:26 > 0:46:28It was his passion for gadgets,
0:46:28 > 0:46:31for things that he could adapt and change,
0:46:31 > 0:46:33that led him to his greatest invention,
0:46:33 > 0:46:36a device which is as iconic to behaviourists
0:46:36 > 0:46:39as the telescope is to astronomers -
0:46:39 > 0:46:43the operant conditioning chamber, or Skinner's box.
0:46:45 > 0:46:50Skinner's experiments would reveal something surprising,
0:46:50 > 0:46:55and very disturbing, about the human condition.
0:46:57 > 0:47:01- This is an operant chamber. - Otherwise known as a Skinner box.
0:47:01 > 0:47:03It's a Skinner box. Many people in my field...
0:47:03 > 0:47:07'Dr Robert Allan uses similar methods to those Skinner used.'
0:47:07 > 0:47:10Here's an area where the pigeon stands.
0:47:10 > 0:47:11Their response keys...
0:47:11 > 0:47:14'The pigeon has to peck on these buttons.
0:47:14 > 0:47:18'If it pecks them in the right order, it gets a reward.'
0:47:18 > 0:47:21So what are you going to do to impress me with the pigeon today?
0:47:21 > 0:47:24I'll show you. Let's go get a pigeon.
0:47:24 > 0:47:26Who's this?
0:47:26 > 0:47:29This is G21.
0:47:29 > 0:47:32G21? I don't think of pigeons as being smart, I must admit.
0:47:32 > 0:47:36- They're very smart.- Is he going to demonstrate just how smart?- Indeed.
0:47:36 > 0:47:39- OK. In you go, G21.- OK.
0:47:40 > 0:47:44- Ooh. Is he hungry?- It looks like!
0:47:46 > 0:47:50'The pigeon has to work out whether the centre light
0:47:50 > 0:47:52'shines red or green for longest.
0:47:52 > 0:47:56'If it's green, it has to peck the button on the right.'
0:47:56 > 0:47:57Oh, he's smart.
0:47:57 > 0:48:00Long green means go right.
0:48:00 > 0:48:02OK. So will he go right?
0:48:02 > 0:48:05- Yes, he will.- You're confident in your bird, aren't you?
0:48:05 > 0:48:08- I am very confident. - Ah! Very good.- There you go.
0:48:08 > 0:48:12If it was red that was longest, he has to go the other way.
0:48:12 > 0:48:14Now he has to go left.
0:48:14 > 0:48:15- OK.- Watch.
0:48:15 > 0:48:18Yes, he's done it. He's very good, I have to say.
0:48:18 > 0:48:20I'm good at predicting behaviour.
0:48:20 > 0:48:24Well done, G21. Go, boy, go.
0:48:24 > 0:48:30'What these experiments showed was how easily behaviour could be learned, even manipulated.'
0:48:36 > 0:48:40'I was about to see how quickly this can happen.'
0:48:40 > 0:48:44We are going to shape the turning response
0:48:44 > 0:48:49by delivering reinforcers for his approximate behaviour.
0:48:49 > 0:48:55- You're going to make him sort of turn in a circle, are you? - That's correct. That's better said!
0:48:56 > 0:48:59'Each time the pigeon turns left,
0:48:59 > 0:49:03'Dr Allan delivers food to reinforce that behaviour,
0:49:03 > 0:49:06'until after just 20 minutes,
0:49:06 > 0:49:09'he has the pigeon dancing round in circles.'
0:49:12 > 0:49:16'Pigeons and birdseed may not look controversial,
0:49:16 > 0:49:18'but what was so shocking at the time
0:49:18 > 0:49:22'was that Skinner applied his ideas to human behaviour.'
0:49:24 > 0:49:29What Skinner was saying is that we are in many ways like pigeons -
0:49:29 > 0:49:33that we are the product of the numerous interactions we have with our environment,
0:49:33 > 0:49:37whether it's falling in love, the job, the friends you make,
0:49:37 > 0:49:40all these things which appear to be decisions are actually
0:49:40 > 0:49:43the product of things that have happened to us in the past.
0:49:43 > 0:49:47We can no more exercise free will than this pigeon
0:49:47 > 0:49:50can decide whether to peck, or indeed, turn in a circle.
0:49:55 > 0:50:01Skinner was convinced his discovery could be used to benefit mankind.
0:50:05 > 0:50:11We could change people's behaviour for the better by changing their environment.
0:50:13 > 0:50:18But in the context of the Cold War, the ability to control behaviour
0:50:18 > 0:50:22left some people fearful it could be misused,
0:50:22 > 0:50:27because in Skinner's view, free will was nothing but an illusion.
0:50:32 > 0:50:37Now, most of us believe that being able to make choices is an important part of being human,
0:50:37 > 0:50:40but here was Skinner saying that that was an illusion,
0:50:40 > 0:50:43that actually it was a piece of pre-scientific nonsense,
0:50:43 > 0:50:47akin to believing in a flat Earth or demonic possession.
0:50:47 > 0:50:53You can imagine how popular that message was in the land of the free and the rugged individual.
0:50:56 > 0:51:00Behaviourism was soon joined by other approaches,
0:51:00 > 0:51:02through the 1960s and beyond.
0:51:04 > 0:51:08There were new drugs, therapies, personality tests,
0:51:08 > 0:51:12new ways to measure our thoughts, memories and emotions.
0:51:14 > 0:51:18Psychology has grown into a vast science,
0:51:18 > 0:51:22as diverse and multi-faceted as we are.
0:51:29 > 0:51:32So, who are we?
0:51:33 > 0:51:38Well, we are the product of our genes and our environment.
0:51:45 > 0:51:49Billions of neurochemical reactions
0:51:49 > 0:51:52firing every single second of our lives.
0:51:55 > 0:51:59In us, reason and emotion are frequently at war.
0:52:03 > 0:52:07Thoughts, passions, memories and behaviour
0:52:07 > 0:52:10emerge unbidden out of the depths.
0:52:10 > 0:52:13Brain scans reveal many parts of the brain
0:52:13 > 0:52:16operating outside our conscious awareness.
0:52:27 > 0:52:31We are the product of numerous daily interactions,
0:52:33 > 0:52:39and the quest to understand the essence of who we are
0:52:39 > 0:52:43has revealed something fascinating going on inside our heads,
0:52:43 > 0:52:46something none of us are ever aware of.
0:52:48 > 0:52:54I can show you what I mean with a famous visual illusion.
0:52:57 > 0:52:59HE LAUGHS
0:52:59 > 0:53:02'It's called the Ames room.'
0:53:02 > 0:53:05That is so bizarre!
0:53:05 > 0:53:07Clearly, what I'm seeing is,
0:53:07 > 0:53:11I'm seeing a very, very tall person over there
0:53:11 > 0:53:14and a short person over there, and when they swap over,
0:53:14 > 0:53:18there's a moment when my brain just goes clunk.
0:53:19 > 0:53:25I absolutely know this is an illusion, but my brain just won't let me see through the illusion.
0:53:29 > 0:53:30So how's it done?
0:53:30 > 0:53:33Well, if you come over this way,
0:53:33 > 0:53:35it's really obvious.
0:53:35 > 0:53:39Hi, there. Thank you.
0:53:39 > 0:53:41OK, so essentially,
0:53:41 > 0:53:44the room really dips downhill. Lots of space above my head.
0:53:44 > 0:53:47There is a sharply sloping floor.
0:53:47 > 0:53:53As I march up, the room begins to narrow until I'm really crunched into the corner.
0:53:53 > 0:53:56There's very little space between the ground and the top here,
0:53:56 > 0:53:59and that's how the illusion is created.
0:53:59 > 0:54:04Essentially, the room is a trapezoid.
0:54:06 > 0:54:09The Ames room shows us something very important
0:54:09 > 0:54:11about how the brain is working.
0:54:12 > 0:54:17There's part of my brain which knows the rules of a room.
0:54:17 > 0:54:20It has assumptions, models built in there,
0:54:20 > 0:54:23and it knows, based on experience,
0:54:23 > 0:54:27that normally in rooms, the ceiling and the floor is parallel,
0:54:27 > 0:54:30and that the walls are at a right angle.
0:54:30 > 0:54:33From one particular viewpoint,
0:54:33 > 0:54:36the room looks like it fits that mental model,
0:54:36 > 0:54:41and the brain has such a powerful belief that this quirky-shaped room
0:54:41 > 0:54:45is normal that people appear to have changed size.
0:54:48 > 0:54:53This illusion reveals something fundamental about how the brain works.
0:54:54 > 0:54:59Our perception of reality is not just based on what is out there,
0:54:59 > 0:55:02but it is also partially constructed.
0:55:02 > 0:55:05We have these models running in our head,
0:55:05 > 0:55:09and they are constantly being tested against the evidence of our senses.
0:55:17 > 0:55:22This process of building models in our heads is happening from the moment we are born.
0:55:24 > 0:55:28This child is using her senses to find out about the world.
0:55:31 > 0:55:34Is that person in the mirror another baby, or is it me?
0:55:36 > 0:55:40Why does that thing make a noise when I shake it?
0:55:40 > 0:55:43What she's doing is constantly learning
0:55:43 > 0:55:46by testing everything around her.
0:55:48 > 0:55:51Thousands of little experiments like these
0:55:51 > 0:55:53will create her unconscious assumptions.
0:55:56 > 0:56:01They'll build the models that shape her view of the world.
0:56:01 > 0:56:04That's how she will be able to make her way through life.
0:56:10 > 0:56:14It is very charming when you think that in a way, what she's doing now
0:56:14 > 0:56:17is acting rather like a mini-scientist.
0:56:17 > 0:56:22She's investigating the world, she's forming her theories,
0:56:22 > 0:56:26her hypotheses, and she's testing them against reality.
0:56:26 > 0:56:30'And that, in a sense, is what science is, and it's going on
0:56:30 > 0:56:35'inside each and every one of us from the moment we're born.'
0:56:35 > 0:56:37Is that right, Chloe? Is that right?
0:56:37 > 0:56:39It is.
0:56:44 > 0:56:51In this programme, we've seen that humans are creatures of both rational thought,
0:56:51 > 0:56:53and emotional turmoil.
0:56:55 > 0:56:59And in this series, I've shown how science too
0:56:59 > 0:57:01has been shaped by reason and emotion,
0:57:01 > 0:57:07as well as by the tumult of the world in which it operates.
0:57:09 > 0:57:13Its intellectual achievements have transformed our lives.
0:57:21 > 0:57:25But it hasn't been straightforward.
0:57:25 > 0:57:28The story of science is a messy one,
0:57:28 > 0:57:33wrapped up in politics, belief, money and rivalry,
0:57:33 > 0:57:36proof forever shaped by power and passion.
0:57:40 > 0:57:44Science is a very human activity,
0:57:44 > 0:57:48something we unconsciously do every day -
0:57:48 > 0:57:54observing the world, building mental models, and testing them.
0:57:55 > 0:57:59But it's when we deliberately started using the scientific method
0:57:59 > 0:58:03that we went way beyond our individual capabilities.
0:58:05 > 0:58:09I think science is the greatest collective endeavour
0:58:09 > 0:58:12that mankind has ever undertaken.
0:58:18 > 0:58:21Over the last few thousand years,
0:58:21 > 0:58:23the human brain has not changed at all.
0:58:23 > 0:58:25Evolution does not go that fast.
0:58:25 > 0:58:29But what has changed is our understanding of the world.
0:58:29 > 0:58:33We don't have to rely simply on the wisdom of our own brains.
0:58:33 > 0:58:34SHE GURGLES
0:58:34 > 0:58:37We have language, we have literature,
0:58:37 > 0:58:41and now we have computers, and that links us all together.
0:58:41 > 0:58:43That gives us, if you like,
0:58:43 > 0:58:46the wisdom of all those who have gone before.
0:58:56 > 0:59:00Subtitles by Red Bee Media Ltd
0:59:00 > 0:59:03E-mail subtitling@bbc.co.uk