0:00:03 > 0:00:05There are some great questions
0:00:05 > 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 > 0:00:20How did we get here?
0:00:24 > 0:00:27What is the world made of?
0:00:30 > 0:00:36The story of our search to answer those questions is the story of science.
0:00:38 > 0:00:42Of all human endeavours, science 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 > 0:00:53Its ideas, its achievements, its results are all around us.
0:00:53 > 0:00:58So, how did we arrive at the modern world?
0:00:58 > 0:01:02Well, that is more surprising and more human than you might think.
0:01:07 > 0:01:11The history of science is often told as a series of eureka moments,
0:01:11 > 0:01:14the ultimate triumph of the rational mind.
0:01:14 > 0:01:17But the truth is that power and passion,
0:01:17 > 0:01:23rivalry and sheer blind chance have played equally significant parts.
0:01:25 > 0:01:31In this series, I'll be offering a different view of how science happens.
0:01:31 > 0:01:36It's been shaped as much by what's outside the laboratory as inside.
0:01:39 > 0:01:44This is the story of how history made science and science made history
0:01:44 > 0:01:47and how the ideas that were generated changed our world.
0:01:48 > 0:01:51It is a tale of power...
0:01:52 > 0:01:54..proof...
0:01:54 > 0:01:56and passion.
0:02:05 > 0:02:09This time, perhaps the greatest puzzle of existence.
0:02:12 > 0:02:15What is the secret of life?
0:02:21 > 0:02:26Inside every one of us there lies a mystery.
0:02:28 > 0:02:35Something creates the rich and intense experience of being alive.
0:02:37 > 0:02:39But what exactly is it?
0:02:42 > 0:02:47What is it that makes a living thing so utterly different from a non-living thing?
0:02:48 > 0:02:53The struggle to explain the sheer wonder of life
0:02:53 > 0:02:59has been one of the most productive challenges science has ever faced.
0:03:01 > 0:03:08But the search for answers has also proved tantalising and elusive.
0:03:11 > 0:03:17This is the story of how we came to understand many of the secrets of life by studying the creature
0:03:17 > 0:03:20that interests us the most, ourselves.
0:03:36 > 0:03:43Across the ancient world, there were long-running arguments about what constitutes life.
0:03:45 > 0:03:50One particular view came to dominate Western thought.
0:03:53 > 0:03:58For 1,500 years, physicians in the West slavishly followed the ideas
0:03:58 > 0:04:01of a Roman called Claudius Galen.
0:04:01 > 0:04:05Now, he's undoubtedly one of the most influential thinkers in history.
0:04:05 > 0:04:09Born not long after the death of Jesus of Nazareth,
0:04:09 > 0:04:14his books were still being used by doctors well into the 17th century.
0:04:14 > 0:04:18His ideas about life were shaped by one of the most bloody
0:04:18 > 0:04:21and violent spectacles provided by the Roman emperor.
0:04:24 > 0:04:28For Galen started out as physician to the gladiators.
0:04:31 > 0:04:35Picture the scene - swords clash then bite through flesh.
0:04:35 > 0:04:40Howls of pain from the gladiators would have been drowned by the roar of the crowd.
0:04:40 > 0:04:46This was often a fight to the death, where even for the victor, survival was not always an option.
0:04:48 > 0:04:53Victorious gladiators often had life-threatening injuries.
0:04:53 > 0:04:56Galen was determined to keep them alive.
0:05:00 > 0:05:04Galen did not believe that the matter of life and death
0:05:04 > 0:05:07should be left simply in the hands of the gods.
0:05:07 > 0:05:12He was convinced from personal experience that there were plenty of things a physician could do
0:05:12 > 0:05:15that would preserve and prolong life.
0:05:15 > 0:05:18Trying to understand the workings of the human body
0:05:18 > 0:05:23and write his findings down became his lifelong passion and his legacy.
0:05:25 > 0:05:31He built up a system of medical treatment that was extremely effective.
0:05:33 > 0:05:37His predecessor had lost sixty wounded gladiators.
0:05:37 > 0:05:39Galen only lost four.
0:05:42 > 0:05:48But he wasn't just interested in preserving life, he wanted to explain it.
0:05:50 > 0:05:54Galen was particularly interested in one organ, the liver.
0:05:54 > 0:05:57He had noticed when he was doing his dissections
0:05:57 > 0:05:59that the liver has lots of different vessels going
0:05:59 > 0:06:04in and out of it, and he concluded that the liver produces all the blood
0:06:04 > 0:06:08in the human body and it's drawn from the liver and spread around.
0:06:10 > 0:06:17He also believed that blood contains within it spirits - the spirits come from the liver, they also come from
0:06:17 > 0:06:23the heart and from the brain, and it's these spirits that give blood the essence of life.
0:06:25 > 0:06:29He wrote 300 books and pamphlets
0:06:29 > 0:06:33covering almost everything about the human body and how it works.
0:06:33 > 0:06:36It was encyclopaedic.
0:06:36 > 0:06:40But it was also fundamentally flawed.
0:06:42 > 0:06:47Now, Galen's entire system was based on his anatomical studies.
0:06:47 > 0:06:53The only thing was that he himself, as far as we know, never did any human dissections.
0:06:53 > 0:06:58He relied on cutting up animals, such as pigs and Barbary apes.
0:07:01 > 0:07:06Nevertheless, his system was seen as superior to anything else.
0:07:08 > 0:07:11He became wealthy and hugely influential.
0:07:18 > 0:07:25Remarkably, a set of beliefs about the body laid down by one man in ancient Rome
0:07:25 > 0:07:28went on to become medical gospel.
0:07:30 > 0:07:37For more than a thousand years, Galen's work provided THE reference book of life
0:07:37 > 0:07:41until developments in Renaissance Italy
0:07:41 > 0:07:43changed the way we see the world.
0:08:03 > 0:08:06It may not look very impressive from here, but I'm actually
0:08:06 > 0:08:09standing in-between the inner and the outer wall of what I think is one
0:08:09 > 0:08:15of the most beautiful buildings in the world, and the view is certainly going to be worth going to see.
0:08:19 > 0:08:22It's the magnificent Duomo in Florence.
0:08:25 > 0:08:31It was built at a time when the city states of Italy were undergoing dramatic change.
0:08:31 > 0:08:37These upheavals would go on to affect our understanding of life.
0:08:37 > 0:08:41One change in particular began here, with an architect.
0:08:43 > 0:08:48The dome I'm standing on was designed and built by Filippo Brunelleschi,
0:08:48 > 0:08:51one of the most influential figures of the Renaissance.
0:08:51 > 0:08:56The Renaissance was a period of rebirth, the liberating of the human imagination.
0:08:56 > 0:09:01Brunelleschi was one of those polymaths, those brilliant geniuses
0:09:01 > 0:09:07that the Renaissance just simply seemed to spawn effortlessly - engineer, architect, mathematician.
0:09:07 > 0:09:14Many of the skills he used to build this dome he also used to create a new vision of reality.
0:09:16 > 0:09:20He introduced a new way of seeing the world.
0:09:20 > 0:09:23It involved mathematics.
0:09:23 > 0:09:28Using the cathedral buildings, he demonstrated how it worked.
0:09:32 > 0:09:36What Brunelleschi did is he drew a painting, like this one of the Baptistery -
0:09:36 > 0:09:39actually, probably rather better than this one -
0:09:39 > 0:09:43and he took a mirror and he got his friends to try this trick.
0:09:43 > 0:09:47You look through a hole there, then you try and line up
0:09:47 > 0:09:49the mirror with the buildings.
0:09:49 > 0:09:53Now, it's a very
0:09:53 > 0:09:57charming little trick, this one, because you realise when you do this
0:09:57 > 0:10:05that the painting is actually a very good three-dimensional representation of that building.
0:10:06 > 0:10:11It's so realistic because of his novel approach to painting.
0:10:11 > 0:10:17Lines which are actually parallel he drew as converging to a vanishing point.
0:10:19 > 0:10:23This was counterintuitive - to many, it still is -
0:10:23 > 0:10:26but this made the painting accurately reflect
0:10:26 > 0:10:29what was seen in the real world.
0:10:31 > 0:10:35It was the start of modern perspective painting. Hm!
0:10:40 > 0:10:45The understanding of perspective didn't just affect art and architecture,
0:10:45 > 0:10:49it also profoundly altered the way that people viewed the human body.
0:10:52 > 0:10:56It created a new hunger for realism.
0:11:13 > 0:11:19The impact of the new approach can be seen on the bodies locked away in Windsor Castle.
0:11:22 > 0:11:26The castle houses around 600 drawings by Leonardo da Vinci,
0:11:26 > 0:11:29beautiful, exquisite drawings of the human body.
0:11:29 > 0:11:34And I'm really excited, because I've seen copies but I've never seen the originals.
0:11:41 > 0:11:45The detail is astonishing.
0:11:48 > 0:11:52These drawings are over 500 years old.
0:11:55 > 0:11:57I must admit, I do feel a shiver.
0:11:57 > 0:12:02There is something about holding it and thinking of him doing this.
0:12:05 > 0:12:09In these pen strokes, you can see something ground-breaking.
0:12:12 > 0:12:17Here, he started to cut muscles away and lift them away from their points of insertion and origin and so on
0:12:17 > 0:12:20to show how the bones are connected to them, to the muscles.
0:12:20 > 0:12:23It's that sort of diagrammatic innovation
0:12:23 > 0:12:25which is so impressive of his time.
0:12:25 > 0:12:27And so three-dimensional.
0:12:27 > 0:12:29- Mm.- The perspective on it is just extraordinary.
0:12:29 > 0:12:34Well, uniquely, he was able to unite this anatomical understanding with
0:12:34 > 0:12:37artistic ability, and it's why these drawings are still so impressive.
0:12:37 > 0:12:39Mm.
0:12:41 > 0:12:44Leonardo's drawings are wonderfully realistic.
0:12:47 > 0:12:52Very different from many pre-Renaissance drawings of the body,
0:12:52 > 0:12:55which tended to be stylised or symbolic.
0:12:57 > 0:13:03And Leonardo drew bodies for reasons that went well beyond art.
0:13:03 > 0:13:08I mean, this really is an evocation of life, and he was really trying to understand life.
0:13:08 > 0:13:12Understanding where life came from or what made a living being rather
0:13:12 > 0:13:17than a static being was of fundamental importance to Leonardo.
0:13:23 > 0:13:30Those are exquisite drawings by an exceptional artist, but they're also more than that.
0:13:30 > 0:13:33They are, if you like, the beginnings of a period
0:13:33 > 0:13:37when people began to truly understand the human body.
0:13:40 > 0:13:46Artists helped give a fresh impetus to the study of human anatomy.
0:13:48 > 0:13:52Knowing what's really beneath the skin would open up new avenues
0:13:52 > 0:13:55in the quest to explain the living body.
0:14:14 > 0:14:19Anatomy studies flourished in the Italian town of Padua,
0:14:19 > 0:14:22one of the great centres of learning in the 16th century.
0:14:26 > 0:14:29Students flocked here from all over Europe.
0:14:29 > 0:14:34They came because it was lively, it was vibrant, but also because they could get access to something
0:14:34 > 0:14:39which was in extremely short supply everywhere else, dead human bodies.
0:14:42 > 0:14:49Medical students who came here were not content to rely on animals.
0:14:49 > 0:14:52They wanted to study humans.
0:15:05 > 0:15:08Imagine, if you will,
0:15:08 > 0:15:13200 students crammed layer after layer after layer.
0:15:13 > 0:15:17But the star of the show was down here on a marble slab,
0:15:17 > 0:15:19a dead human body.
0:15:22 > 0:15:28They were normally freshly executed malefactors, ne'er-do-wells, criminals.
0:15:33 > 0:15:39The university was not constrained by religious limits placed on human dissection.
0:15:39 > 0:15:42It was independent of the Church.
0:15:45 > 0:15:48What was striking about the dissections performed here
0:15:48 > 0:15:52was not only they were more frequent, but they were also done in a completely different way.
0:15:52 > 0:15:56Now, the old way, which had been done for many centuries, was the professor
0:15:56 > 0:15:59would read from Galen's book, saying,
0:15:59 > 0:16:01"Here's a liver, three lobes,"
0:16:01 > 0:16:04the demonstrator would show the liver, which plainly didn't have
0:16:04 > 0:16:09three lobes, but all the students would basically nod and agree.
0:16:09 > 0:16:12And I can sort of understand that, because when I was a medical student
0:16:12 > 0:16:15there was a tremendous pressure to conform.
0:16:15 > 0:16:17But here in Padua, things were different.
0:16:17 > 0:16:21People were encouraged to describe what they actually saw
0:16:21 > 0:16:25as opposed to what Galen's book said they should see.
0:16:27 > 0:16:34This new style of anatomy lesson was a brazen challenge to accepted wisdom.
0:16:34 > 0:16:37It had been pioneered by Andreas Vesalius,
0:16:37 > 0:16:42who was made Professor of Surgery and Anatomy aged just 23.
0:16:44 > 0:16:48He'd published a detailed atlas of the human body.
0:16:51 > 0:16:54A new book of life.
0:17:09 > 0:17:13Based on his own careful observations,
0:17:13 > 0:17:19Vesalius boldly corrected mistake after mistake in orthodox beliefs.
0:17:21 > 0:17:23Come and have a look at this.
0:17:23 > 0:17:27Vesalius noticed a number of anatomical features that were
0:17:27 > 0:17:31wrong in Galen's descriptions, for example the jaw bone.
0:17:31 > 0:17:37Now, Vesalius correctly recognised that humans have a single bone that forms the jaw,
0:17:37 > 0:17:38it's not split in two.
0:17:38 > 0:17:42You get that in dogs. Then there were the number of ribs.
0:17:42 > 0:17:45Vesalius recognised and demonstrated that men
0:17:45 > 0:17:47have the same number of ribs
0:17:47 > 0:17:53as women, not, as some people claimed, one less, because, obviously, the Bible says God took
0:17:53 > 0:17:56one of man's ribs and made Eve out it.
0:17:56 > 0:18:00But Vesalius demonstrated quite clearly that if he did, he obviously grew a new one.
0:18:00 > 0:18:04And then we had the thigh bone.
0:18:04 > 0:18:07Galen had claimed that the thigh bone was curved,
0:18:07 > 0:18:09again because he saw that in dogs,
0:18:09 > 0:18:13whereas Vesalius correctly recognised that it's straight.
0:18:13 > 0:18:18Some people found it so hard to accept that Galen could possibly have been wrong.
0:18:18 > 0:18:20They claimed that the straightening of the thigh bone
0:18:20 > 0:18:24must have been caused by a recent fashion for wearing tight trousers.
0:18:28 > 0:18:33But Vesalius did more than simply correct Galen's errors.
0:18:33 > 0:18:37What is so special about his work is his approach.
0:18:40 > 0:18:46He carefully observed, stripping away layer after layer.
0:18:47 > 0:18:53This would start Western medical science on a distinct and powerful course.
0:18:54 > 0:19:00From now on, the essence of life would be sought by looking deeper and deeper into the body,
0:19:00 > 0:19:04breaking it down into its component parts,
0:19:04 > 0:19:11an approach that would in time lead to major advances
0:19:11 > 0:19:12in medicine
0:19:12 > 0:19:14and in surgery.
0:19:18 > 0:19:24In many ways, here in Padua they laid the foundations for a new understanding of life.
0:19:24 > 0:19:26But anatomy is not the full story.
0:19:26 > 0:19:31There's also the question of how does the body work, the processes, physiology.
0:19:33 > 0:19:38The search for the secret of life turned from simply observing
0:19:38 > 0:19:43the structure of the body to trying to find out how it works.
0:19:44 > 0:19:51That would require a very different approach, one based on experiment.
0:19:59 > 0:20:03England, a thousand miles from Renaissance Italy.
0:20:05 > 0:20:08A country riven by religious and political differences.
0:20:12 > 0:20:1617th century England was heading for civil war.
0:20:21 > 0:20:25There was tension between old and new,
0:20:25 > 0:20:31a conflict embodied in the inquisitive mind of a London physician.
0:20:40 > 0:20:45William Harvey was not a radical, he was not looking to cause a stir.
0:20:45 > 0:20:48But like a detective who comes across something he can't explain,
0:20:48 > 0:20:52he gathered evidence, he collected clues, until finally,
0:20:52 > 0:20:59he had built such a powerful case that he brought Galen's remaining system clattering to the floor.
0:20:59 > 0:21:05For me, William Harvey is one of the greats, a founding father of modern experimental medicine.
0:21:10 > 0:21:15Harvey had learnt the advantages of a probing, questioning approach
0:21:15 > 0:21:18when he was a student at Padua University.
0:21:20 > 0:21:25But where Vesalius had just observed, Harvey went further.
0:21:25 > 0:21:26He investigated.
0:21:38 > 0:21:41He questioned the widely accepted belief
0:21:41 > 0:21:46that blood is made by the liver and consumed by the rest of the body.
0:21:48 > 0:21:54Harvey conducted a series of experiments, studying animals living and dead.
0:21:57 > 0:22:04One of his most famous experiments was to calculate the volume of blood that passes through the heart.
0:22:06 > 0:22:12Now, I've got a pig's heart here, which is about the same volume as a human heart.
0:22:12 > 0:22:17Fill it with some nice fake blood and then...
0:22:19 > 0:22:21..tip it in there.
0:22:21 > 0:22:24Ooh, gorgeous!
0:22:25 > 0:22:29And then - this is really quite unpleasant and quite gunky -
0:22:29 > 0:22:31now you've got to weigh it,
0:22:31 > 0:22:35which involves somehow getting the glove off
0:22:35 > 0:22:37and this onto some scales.
0:22:37 > 0:22:39I've pre-weighed the glass.
0:22:41 > 0:22:44Right, that's just...
0:22:44 > 0:22:46over two ounces.
0:22:47 > 0:22:52Harvey did some quick calculations based on how often the heart beats
0:22:52 > 0:22:56and came up with a figure of 500 ounces.
0:22:56 > 0:23:01That's how much blood is passing through the heart every half an hour.
0:23:01 > 0:23:06It is more than the entire volume of blood in the human body.
0:23:08 > 0:23:13Harvey's figures showed that the heart can propel an astonishing
0:23:13 > 0:23:164,000 litres of blood every single day.
0:23:20 > 0:23:24That's an awful lot of blood.
0:23:25 > 0:23:33Now, if accepted wisdom was correct, then the body was making and using up this much blood
0:23:33 > 0:23:35every 24 hours.
0:23:38 > 0:23:42This, plus all the other experiments he'd done, suggested to Harvey
0:23:42 > 0:23:44there could only be one explanation,
0:23:44 > 0:23:48that the blood circulates around the body.
0:23:48 > 0:23:51This went completely against everything he had been taught,
0:23:51 > 0:23:54but he had to trust the evidence of his own eyes.
0:23:56 > 0:24:02Harvey concluded that the heart's real function was to propel blood around the body.
0:24:04 > 0:24:08The heart was no longer purely a mysterious organ that infuses blood
0:24:08 > 0:24:10with the essence of life.
0:24:12 > 0:24:14It was now more like a pump.
0:24:18 > 0:24:25Harvey proved that the blood circulates round the body and overthrew 1,500 years of dogma.
0:24:25 > 0:24:27But perhaps more importantly than that,
0:24:27 > 0:24:33he established the experimental method, which is still crucial to science today.
0:24:33 > 0:24:39He also inadvertently opened the door to a new understanding of life.
0:24:42 > 0:24:47It was a more physical explanation of how the body works.
0:24:56 > 0:25:02This change was born out of the realism of perspective painting,
0:25:02 > 0:25:06a new observational school of anatomy
0:25:06 > 0:25:08and Harvey's experimental method.
0:25:10 > 0:25:16The stage was set for a more materialistic approach to the body and to life.
0:25:30 > 0:25:35This town clock near Padua was built in the 17th century,
0:25:35 > 0:25:40a time when mechanics was helping explain the world around us.
0:25:42 > 0:25:48Men like Galileo and Newton were offering a completely new view of the cosmos
0:25:48 > 0:25:51based on mathematics and physics.
0:25:53 > 0:25:57Its internal workings were likened to those of a clock -
0:25:57 > 0:26:05cogs, weights, pulleys, simple components that together make a complex machine.
0:26:07 > 0:26:13People began to wonder if there were things in nature that were also driven by hidden clockwork,
0:26:13 > 0:26:17whether nature itself moved to the beat of a mechanical drum.
0:26:19 > 0:26:21Could the same be true of us?
0:26:23 > 0:26:26Are we just mechanical beings?
0:26:28 > 0:26:33Go on, test me, give me another on another finger.
0:26:33 > 0:26:36- OK! It doesn't hurt a bit!- OK!
0:26:36 > 0:26:40An Italian mathematician called Giovanni Borelli took the rigorous
0:26:40 > 0:26:43analytical methods from mechanics
0:26:43 > 0:26:46and applied them to the study of life.
0:26:49 > 0:26:51- OK.- OK, we're up to eleven.
0:26:51 > 0:26:53OK.
0:26:53 > 0:26:55Pick another one, go on.
0:26:57 > 0:26:59- OK!- OK! - Go ahead and bring your arm down.
0:26:59 > 0:27:01Oh, that's really easy now.
0:27:01 > 0:27:03Yeah, it's much, much easier.
0:27:03 > 0:27:10In his attempts to understand the body, Borelli broke it down into simple components.
0:27:11 > 0:27:16Borelli described the body as a set of levers and pulleys,
0:27:16 > 0:27:19so these pulleys here connect the two levers,
0:27:19 > 0:27:23which are the bones of the body, and around the pulley goes a rope,
0:27:23 > 0:27:26and that's how he described the muscles of the body.
0:27:26 > 0:27:32He deduced that our musculoskeletal system is less about strength,
0:27:32 > 0:27:34more about movement.
0:27:34 > 0:27:37Because it's attached here, just a small movement in the muscle,
0:27:37 > 0:27:39a small contraction, creates a huge motion.
0:27:39 > 0:27:43Ah! But you have to have quite a lot of force to do it, because it's closer to that.
0:27:43 > 0:27:49- Exactly.- But you can get quite a lot of movement from a relatively short...- You get a lot of motion.
0:27:49 > 0:27:56It was a significant step towards explaining how our bodies really work.
0:27:56 > 0:28:01Having broken it down, Borelli could now put the body back together again.
0:28:11 > 0:28:13It's very clever, isn't it?
0:28:16 > 0:28:18Er, right, where is that coming out?
0:28:18 > 0:28:22Oh, yes.
0:28:24 > 0:28:25Here we go. There we go. Ta-da!
0:28:28 > 0:28:32Fabulous! And Borelli didn't just look at movement,
0:28:32 > 0:28:35he analysed the internal organs, too,
0:28:35 > 0:28:40calculating the volume of the lungs and the force of the pumping heart.
0:28:43 > 0:28:47- So this is, I suppose, the development of the idea of man as a machine, which is...- Absolutely.
0:28:47 > 0:28:52- ..a very useful metaphor, isn't it? - Yeah. It's really ingenious how he broke the body down into such
0:28:52 > 0:28:58simple components and could come up with quite ingenious reasons for how the body works.
0:29:05 > 0:29:10So here you have it, a human arm stripped down to its bare essentials.
0:29:10 > 0:29:15Borelli really had shown that you could describe the human body in mechanical terms.
0:29:15 > 0:29:21It was a machine - an incredibly sophisticated machine, but a machine nonetheless.
0:29:27 > 0:29:31Borelli inspired a new science of biomechanics.
0:29:34 > 0:29:37The living body broken down
0:29:37 > 0:29:39into component parts...
0:29:42 > 0:29:49..life reduced to simple physical laws.
0:29:51 > 0:29:56For those who believed in the mechanical body, there was a significant problem.
0:29:56 > 0:30:01Now, this clock needs to be wound up every 47 hours,
0:30:01 > 0:30:04otherwise it simply... stops.
0:30:04 > 0:30:09But what is the equivalent in the human body?
0:30:09 > 0:30:12What is the life force that drives you and me?
0:30:14 > 0:30:21This question rekindled an ancient idea known as vitalism,
0:30:21 > 0:30:26the belief that there was something more to life than a physical body,
0:30:26 > 0:30:28something intangible.
0:30:33 > 0:30:38In the 18th century, many believed that extra something
0:30:38 > 0:30:42might lie in the very latest scientific marvel.
0:30:47 > 0:30:49Electricity.
0:30:49 > 0:30:53No-one knew quite what it was,
0:30:53 > 0:30:56no-one knew quite where it came from.
0:30:57 > 0:31:00All over Europe, people were investigating electricity,
0:31:00 > 0:31:03and they were making some extraordinary claims,
0:31:03 > 0:31:08for example that you could use it to make your fruit trees bear more fruit.
0:31:08 > 0:31:11You could also use it to make your dinner a bit more tasty.
0:31:11 > 0:31:16But what really grabbed people's imagination was the idea that it was electricity
0:31:16 > 0:31:21that was responsible for bringing the cold machine of the body to life.
0:31:23 > 0:31:27In the 1780s, a physician called Luigi Galvani
0:31:27 > 0:31:32had made one of the most perplexing and important discoveries of the century.
0:31:35 > 0:31:40He had found that touching frogs' legs with different metals
0:31:40 > 0:31:41would make them twitch.
0:31:43 > 0:31:47I can remember when I was a medical student and we first started
0:31:47 > 0:31:51using electrical currents on frogs' legs, and I saw one twitch like that.
0:31:51 > 0:31:56It was incredibly disturbing, because I knew it was dead but it seemed to be coming to life.
0:31:56 > 0:32:03Now, Galvani himself was convinced that electricity was being generated from within the tissue of the frog.
0:32:03 > 0:32:08He called it "animal electricity", and he saw a very powerful connection
0:32:08 > 0:32:12between electricity, animation and life itself.
0:32:13 > 0:32:21Galvani claimed to have discovered the vital force, the thing that makes tissue alive.
0:32:23 > 0:32:27Was this evidence of a link between matter and spirit?
0:32:28 > 0:32:33Could animal electricity be the spark of life?
0:32:39 > 0:32:45Across Europe, eminent researchers set out to find out.
0:32:47 > 0:32:50One man who took it to extremes
0:32:50 > 0:32:55was the German scholar Alexander von Humboldt.
0:32:57 > 0:33:01He was one of the great romantic figures of his time.
0:33:01 > 0:33:06His epic journeys around South America made him famous.
0:33:06 > 0:33:12Charles Darwin described him as "the greatest scientific traveller who ever lived".
0:33:12 > 0:33:19But his early passion was electricity, and he did numerous experiments on frogs and on himself.
0:33:21 > 0:33:27At Humboldt's old university, I'm in the hands of Dr David Liebetanz.
0:33:27 > 0:33:31We have two channels, and I will activate them separately.
0:33:31 > 0:33:33Tell me when you feel something.
0:33:35 > 0:33:38Nothing? OK, I have to switch it on!
0:33:38 > 0:33:40- Ooh, I could feel a little...- Yeah?
0:33:40 > 0:33:42..little twitch.
0:33:42 > 0:33:47'Von Humboldt wanted to see if animal electricity was the life force
0:33:47 > 0:33:49'that animated the human machine.'
0:33:51 > 0:33:54- Oh!- Finger.
0:33:54 > 0:33:58Gor, lumme! I have no voluntary control over my hands at the moment, and I can't put it down.
0:33:58 > 0:34:02'My muscles are contracting due to carefully controlled electric shocks.
0:34:02 > 0:34:06'In Von Humboldt's time, this was a lot more rudimentary.'
0:34:06 > 0:34:12I know what's going on, but von Humboldt had no idea,
0:34:12 > 0:34:16so this must have been quite literally a major shock for him.
0:34:16 > 0:34:20It's quite strange that it doesn't want to go down.
0:34:20 > 0:34:23Right.
0:34:23 > 0:34:29To recapture the sheer bewildering strangeness of those electrical experiments two hundred years ago,
0:34:29 > 0:34:36David has devised an experiment, adapting his machine to respond to music.
0:34:38 > 0:34:40MUSICAL NOTES PLAY
0:35:03 > 0:35:06Oh, God, thank goodness that is over!
0:35:06 > 0:35:11That was one of the most unpleasant and interesting experiences of my life.
0:35:11 > 0:35:14I had no idea but it looked like, but it felt unbelievably strange.
0:35:14 > 0:35:17I could feel just my face just jumping all over the place.
0:35:17 > 0:35:19Oh, it was nasty!
0:35:19 > 0:35:22- Nasty, nasty, nasty!- But very funny.
0:35:22 > 0:35:25It looked very, very funny.
0:35:25 > 0:35:29That was like possession. Oh, that was really, really unpleasant.
0:35:29 > 0:35:34Unbelievably, Humboldt spent five years doing these sort of experiments.
0:35:34 > 0:35:38In fact, he did over 4,000 of them, and when he published in 1797,
0:35:38 > 0:35:42it caused an absolute sensation throughout Europe.
0:35:46 > 0:35:49Other experimenters agreed.
0:35:49 > 0:35:52This seemed to be evidence of a link between matter and spirit.
0:35:54 > 0:36:00They tried to use electricity to bring the dead back to life,
0:36:00 > 0:36:02and failed.
0:36:03 > 0:36:10However hard they tried, they couldn't impart life to flesh and blood.
0:36:11 > 0:36:17The promise of animal electricity proved to be a false dawn for vitalists.
0:36:29 > 0:36:36The search for the secret of life would require a whole new approach to science.
0:36:48 > 0:36:5119th century Berlin,
0:36:51 > 0:36:54capital of a nation on the rise.
0:36:57 > 0:37:03The Prussian establishment built grand monuments and great armies,
0:37:03 > 0:37:07it invested in industry and technology.
0:37:13 > 0:37:18Prussian aspirations spawned innovative working methods.
0:37:20 > 0:37:24University students, for example, instead of just taking notes,
0:37:24 > 0:37:28now collaborated with their professors on new research,
0:37:28 > 0:37:34and that collaboration was given a suitable home,
0:37:34 > 0:37:35the research laboratory.
0:37:39 > 0:37:43This was when the modern idea of the research laboratory was born.
0:37:43 > 0:37:47Instead of lone geniuses, there would be teams of scientists
0:37:47 > 0:37:51tackling problems, doing experiments, having their results peer-reviewed.
0:37:54 > 0:37:59This change in the way that science is managed and carried out
0:37:59 > 0:38:05would prove to be just as important as any individual discovery.
0:38:06 > 0:38:13Scientific research would now be organised, systemised, legitimised.
0:38:15 > 0:38:19All this would have a direct effect on the future of biology.
0:38:19 > 0:38:24The research laboratories of Prussia were about to make a series of stunning discoveries,
0:38:24 > 0:38:28discoveries that would fundamentally alter our understanding of life -
0:38:28 > 0:38:30all life, everywhere.
0:38:32 > 0:38:39The new Prussian system exploited a technology that had been invented 200 years before...
0:38:45 > 0:38:47..the microscope.
0:38:50 > 0:38:57One of the first to use it had been Robert Hook in the 17th century.
0:38:57 > 0:39:03His book Micrographia contains illustrations of a hidden world.
0:39:05 > 0:39:11The microscope had revealed the intricate structure of plants,
0:39:11 > 0:39:13snowflakes and natural fibres.
0:39:18 > 0:39:23Insects with body parts on a scale no-one had imagined possible.
0:39:25 > 0:39:29It showed the world in unprecedented detail.
0:39:42 > 0:39:47Now, this isn't the most beautiful picture in this book, but it is without doubt the most important.
0:39:47 > 0:39:54It's actually a slice of cork, and when Hook looked at it, he could see all these funny little boxes.
0:39:54 > 0:39:57For reasons best known to himself, he decided they looked like
0:39:57 > 0:40:03rooms he had seen in a monastery, so he gave them the same name, cells.
0:40:04 > 0:40:09At the time, no-one realised the true significance of what he had seen,
0:40:09 > 0:40:15and the idea of the cell would languish in obscurity for 200 years.
0:40:19 > 0:40:24The cell finally resurfaced in the mid-19th century
0:40:24 > 0:40:27in the research laboratories of Prussia.
0:40:33 > 0:40:39There were now well-engineered microscopes on every laboratory bench,
0:40:39 > 0:40:41used to expose new wonders.
0:40:46 > 0:40:49And researchers now saw cells, not just in cork,
0:40:51 > 0:40:55but in other plants and in animals.
0:40:58 > 0:41:02In fact, they saw cells in every living thing.
0:41:07 > 0:41:11This was an absolutely incredible claim.
0:41:11 > 0:41:17Even now, it is hard to grasp that every living thing, whatever its outward appearance,
0:41:17 > 0:41:21from an ant to an elephant, from a blade of grass to my thumb,
0:41:21 > 0:41:24is made up of the same basic structures.
0:41:24 > 0:41:28But the revelations about the cell had only just begun.
0:41:31 > 0:41:38A little-known German called Robert Remak observed and recorded a remarkable process.
0:41:38 > 0:41:43Studying frogspawn, he saw the single egg divide...
0:41:45 > 0:41:46..and divide again.
0:41:50 > 0:41:55Seen in time lapse, at first the cells are simply replicating.
0:42:03 > 0:42:07Then, slowly, the cells start to specialise
0:42:07 > 0:42:11and form the different body parts of the juvenile frog.
0:42:22 > 0:42:26And it isn't just the tadpole that grows like this.
0:42:32 > 0:42:36And what is true of frogs is also true of us.
0:42:36 > 0:42:41It is an extraordinary thought that every one of the trillions of cells
0:42:41 > 0:42:43that make up my body
0:42:43 > 0:42:47originally came from just a single cell.
0:42:52 > 0:42:57The microscope had revealed two fundamental rules of life -
0:43:01 > 0:43:05every living thing on the planet is made of cells...
0:43:07 > 0:43:11..and cells only come from other cells.
0:43:14 > 0:43:19Understand the cell and you'd understand what life was.
0:43:26 > 0:43:31Except it wasn't as easy as all that,
0:43:31 > 0:43:36because even with the best microscopes
0:43:36 > 0:43:39this is all they could see,
0:43:41 > 0:43:44a nucleus in a translucent mush.
0:43:57 > 0:44:04If biologists were to make further progress, they had to find a way to make the invisible visible.
0:44:04 > 0:44:07They would need help, and they would get it
0:44:07 > 0:44:12from two very different worlds, theoretical physics and fashion.
0:44:17 > 0:44:23In the 1850s, the first synthetic dyes burst onto the scene,
0:44:25 > 0:44:30creating a whole new range of colours.
0:44:30 > 0:44:33Fashion drove demand.
0:44:33 > 0:44:37Painting and the arts were also revitalised.
0:44:42 > 0:44:49Artificial colours were made on an industrial scale by German chemists.
0:44:49 > 0:44:56They not only stained clothes, they also stained cells.
0:44:56 > 0:44:59Different colours were made with different chemicals,
0:44:59 > 0:45:04which meant each dye would stain a different part of the cell.
0:45:06 > 0:45:10Structures now began to appear within the translucent mush.
0:45:10 > 0:45:14Surely one of these must contain the secret of life.
0:45:14 > 0:45:19The reductionist journey, probing deeper and deeper into the body,
0:45:19 > 0:45:24now began to gather pace as researchers delved into the cell.
0:45:27 > 0:45:34They discovered internal membranes, protein structures and energy stores.
0:45:34 > 0:45:38But what stood out inside the nucleus
0:45:38 > 0:45:40were chromosomes.
0:45:42 > 0:45:49Chromosomes, meaning "coloured bodies", were named after the dyes that had helped reveal them,
0:45:49 > 0:45:54and they clearly played a crucial role when a cell divides and replicates.
0:45:57 > 0:46:02It seemed this was where the secret of life must lie.
0:46:08 > 0:46:12This new unit of life, the chromosome,
0:46:12 > 0:46:17had emerged from the rise of Germany as a world power,
0:46:17 > 0:46:20its creation of research laboratories
0:46:20 > 0:46:26and its investment in the chemical dye industry.
0:46:26 > 0:46:32These factors had brought us tantalisingly close to a new understanding of life.
0:46:38 > 0:46:45But it seems as if science never solves one problem without creating ten more.
0:46:49 > 0:46:51Having identified chromosomes,
0:46:51 > 0:46:57it was clear that researchers would need to find out how they worked,
0:46:57 > 0:46:59how they replicated,
0:46:59 > 0:47:02and that was a massive problem.
0:47:10 > 0:47:14The story of science has never been straightforward.
0:47:19 > 0:47:23The next development seems to have little to do with biology.
0:47:24 > 0:47:30Instead, it featured the world's greatest physicists and mathematicians.
0:47:32 > 0:47:36They were brought together with a single goal,
0:47:36 > 0:47:41a goal they would achieve with devastating success.
0:47:41 > 0:47:47Yet, ironically enough, it was their success and their burning intellectual curiosity which would
0:47:47 > 0:47:52lead to a moral crisis, and one which would have far-reaching impacts
0:47:52 > 0:47:54on the quest to understand what is life.
0:48:08 > 0:48:12It's hard to imagine now, looking at these derelict guard boxes,
0:48:12 > 0:48:18but this was once one of the most highly classified places in the entire United States.
0:48:18 > 0:48:21Through there, there were 50,000 people working on a project
0:48:21 > 0:48:26which was so secret that even the people who lived just down there had no idea what was going on.
0:48:29 > 0:48:34At the time, it did not appear on maps,
0:48:34 > 0:48:37but it consumed more electricity than New York.
0:48:39 > 0:48:46Oak Ridge, Tennessee, was part of the biggest scientific and technological project in history,
0:48:46 > 0:48:49the Manhattan Project.
0:48:49 > 0:48:52And its aim? To create a nuclear bomb.
0:49:00 > 0:49:05The uranium in Little Boy, the bomb that was dropped on Hiroshima,
0:49:05 > 0:49:07was made here in Oak Ridge.
0:49:07 > 0:49:11The bomb contained 64 kilograms of uranium,
0:49:11 > 0:49:15of which less than 0.6 of a gram - that's about this much -
0:49:15 > 0:49:18was turned into pure energy.
0:49:18 > 0:49:20But this was enough.
0:49:37 > 0:49:42There have been few more significant moments for science than this.
0:49:44 > 0:49:46It changed so much.
0:49:49 > 0:49:54The creation of an instrument of death would even shape the science of life.
0:50:00 > 0:50:04Many of the intellectuals behind the project were gentle souls.
0:50:04 > 0:50:09They had gone into physics because of the sublime beauty that could be uncovered,
0:50:09 > 0:50:13but instead they had built bombs that had killed,
0:50:13 > 0:50:18poisoned and mutilated hundreds of thousands of men, women and children.
0:50:18 > 0:50:22They were dreamers who had created their own nightmare.
0:50:22 > 0:50:24Many wanted out of physics.
0:50:24 > 0:50:31It was tainted. They wanted something more life-affirming, and they found it, in biology.
0:50:36 > 0:50:40They took with them their knowledge of atomic structure
0:50:40 > 0:50:44and applied their techniques to the stuff of life.
0:50:47 > 0:50:51After the War, a physicist called Maurice Wilkins came here
0:50:51 > 0:50:58to King's College, London, to study the enigmatic chromosome.
0:50:58 > 0:51:01What Maurice Wilkins started here at King's
0:51:01 > 0:51:05would lead to one of THE great scientific discoveries of the 20th century
0:51:05 > 0:51:08and transform our understanding of life.
0:51:11 > 0:51:16It began innocuously enough, when Wilkins started to investigate
0:51:16 > 0:51:20one of the chemicals found inside chromosomes.
0:51:21 > 0:51:23Let me show you.
0:51:23 > 0:51:31All it takes to extract is a little salt water, some washing-up liquid and a splash of ice-cold alcohol.
0:51:35 > 0:51:37So, this gunky stuff here...
0:51:39 > 0:51:42..is DNA.
0:51:42 > 0:51:43Isn't that wonderful?
0:51:43 > 0:51:45Never seen my own DNA before.
0:51:45 > 0:51:48All you need to make another Michael Mosley.
0:51:50 > 0:51:52Or is it?
0:51:52 > 0:51:57Is DNA alone really the answer?
0:51:58 > 0:52:04Back in the 1950s, they realised that DNA was special, they just didn't know an awful lot about it.
0:52:04 > 0:52:07When Maurice Wilkins started looking into it,
0:52:07 > 0:52:12he decided to approach the problem from a physicist's point of view, looking at the physical structure.
0:52:12 > 0:52:15He was convinced that if you could understand the structure,
0:52:15 > 0:52:19then you could understand, if you like, its function, how it managed to reproduce.
0:52:23 > 0:52:28His weapon of choice was a technique called X-ray diffraction.
0:52:32 > 0:52:37X-rays fired at the DNA hit the molecule and get scattered.
0:52:39 > 0:52:44The pattern of the scattering can be used to calculate the shape of the molecule.
0:52:47 > 0:52:52This, essentially, is a photograph of a molecule's shadow.
0:52:59 > 0:53:06Joining Wilkins' department was one of the best X-ray diffraction experts around, Rosalind Franklin.
0:53:07 > 0:53:10Rosalind Franklin was working with samples of DNA.
0:53:10 > 0:53:13What we have here in this tube is an original sample.
0:53:13 > 0:53:15- Can I?- Yes. It's her handwriting on the tube.
0:53:15 > 0:53:20Here we have now just on a mount made out of a paper clip a drawn fibre,
0:53:20 > 0:53:22if you can see that stretched fibre...
0:53:22 > 0:53:24- Oh...- ..which is still intact there.
0:53:24 > 0:53:28She knew that she was taking the photographs and the data that would eventually prove
0:53:28 > 0:53:30the structure.
0:53:30 > 0:53:32But she had competition.
0:53:32 > 0:53:38In Cambridge, another team was also racing to make sense of DNA.
0:53:38 > 0:53:42Francis Crick, another former physicist,
0:53:42 > 0:53:45and James Watson were building models.
0:53:47 > 0:53:52In April 1953, they published the famous double helix.
0:53:52 > 0:53:56Crick and Watson got the glory,
0:53:56 > 0:54:01but their model was actually inspired by one of Franklin's photographs,
0:54:01 > 0:54:05shown to Watson WITHOUT Franklin's knowledge.
0:54:07 > 0:54:09Her famous one is this one here...
0:54:09 > 0:54:14- Right.- ..the famous photograph, 51...- Right.- ..which was shown to Jim Watson...- Indeed.
0:54:14 > 0:54:17..by Maurice Wilkins in early 1953.
0:54:21 > 0:54:27Now, the reason why structure matters, why it mattered that there were these two
0:54:27 > 0:54:29strands which were closely entwined,
0:54:29 > 0:54:34is because it neatly explains how a cell divides, how it replicates.
0:54:34 > 0:54:40And until now, that had been one of biology's greatest mysteries.
0:54:42 > 0:54:47The flurry of research which followed revealed DNA's far-reaching influence on life.
0:54:49 > 0:54:55It controls the layout of our bodies and the workings of our biochemistry.
0:54:55 > 0:54:58It reveals our ancestry.
0:55:00 > 0:55:04It may soon direct our medical treatment.
0:55:08 > 0:55:12DNA is the foundation of a new science of life.
0:55:17 > 0:55:23Now, for a while, people must have thought that they had the secret of life within their grasp,
0:55:23 > 0:55:27but the more they looked into DNA, the more complicated it got.
0:55:27 > 0:55:30Life is not as simple as all that.
0:55:35 > 0:55:41In the last 50 years, we've learned how to use and manipulate DNA.
0:55:41 > 0:55:44We can now do the previously unthinkable -
0:55:44 > 0:55:48create it in the laboratory from simple chemicals
0:55:48 > 0:55:55and make new forms of life by inserting synthetic DNA into bacterial cells.
0:55:56 > 0:56:01But we've also discovered that DNA is not all powerful.
0:56:01 > 0:56:04It is a set of instructions,
0:56:04 > 0:56:09but instructions that can be modified by other parts of the same cell.
0:56:12 > 0:56:18This circular feedback means life cannot be pinned down to one component.
0:56:20 > 0:56:22DNA cannot operate in isolation.
0:56:22 > 0:56:28It needs all the chemicals, proteins and energy sources that naturally surround it.
0:56:28 > 0:56:33In short, to create life you absolutely need the whole cell.
0:56:36 > 0:56:42The process of delving ever deeper into the body has revealed so much.
0:56:45 > 0:56:47It has created modern biology.
0:56:52 > 0:56:58But it's also shown that the secret of life does not lie in simplicity,
0:56:58 > 0:57:01in any one chemical or process.
0:57:01 > 0:57:06The essence of life lies in complexity.
0:57:07 > 0:57:12The hope of finding easy answers has slipped away.
0:57:18 > 0:57:20But I'm optimistic.
0:57:20 > 0:57:26I'm convinced that one day we WILL understand how the components of the cell combine.
0:57:26 > 0:57:30We may even be able to create life from scratch.
0:57:30 > 0:57:36However, that will be primitive, just one cell.
0:57:38 > 0:57:40It is a massive step from that to this,
0:57:40 > 0:57:46the billions of cells that make up my body and which communicate with each other in ways
0:57:46 > 0:57:49that at the moment we have not even begun to grasp.
0:57:49 > 0:57:55We have gone on an enormous journey to get where we are today, but when it comes to understanding
0:57:55 > 0:57:59the complexity of life, I think we still have a huge way to go.
0:58:07 > 0:58:14In the final programme, the most intimate question of them all - who are we?
0:58:30 > 0:58:33Subtitles by Red Bee Media Ltd
0:58:33 > 0:58:36E-mail subtitling@bbc.co.uk