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