The Genius of Charles Darwin

Transcription

This series is about perhaps the most powerful idea ever to occur to a human mind. The idea is evolution by natural selection. And the genius who thought of it was Charles Darwin. I'm a biologist and Darwin has been an inspiration to me throughout my whole career. His masterpiece, On The Origin Of Species, was published 150 years ago. And it changed forever our view of the world and our place in it. What Darwin achieved was nothing less than a complete explanation of the complexity and diversity of all life. And yet, it's one of the simplest ideas that anyone ever had. In this series, I want to persuade you that evolution offers a far richer and more spectacular view of life than any religious story. It's one reason why I don't believe in God. I want to show you how Darwin opened our eyes to the extraordinary reality of our world. In this first programme, I'm going to tell you who Charles Darwin was, explain how he discovered his theory of evolution, what it is, and why it matters. By the end, I hope to have convinced you of the truth that evolution is a fact, backed by undeniable evidence. And I want to give you a glimpse of the brutal elegance of the force which, Darwin realised, drives evolution on... ..natural selection. When Charles Darwin was born 200 years ago, sailors and explorers were sending home a dizzying array of specimens like these from all parts of Britain's growing empire. Every animal was believed to have a unique place in God's creation, each made by God according to his perfect, unchanging design. At school in Shrewsbury, the young Charles Darwin was taught that God had created the Earth, and all this rich variety of life just 6,000 years ago. Today, thanks to Darwin, we know differently. But even now, according to polls, four out of every ten British people prefer to cling to the old ideas and believe that God created our world and every living creature in it. I think it's scandalous how little our children are taught about evolution at school. A typical class gets just a few hours to study one of the most important ideas in science. This lot got me. I went to meet a science class of 15 to 16-year-olds at Park High School in London to try to open their eyes to Darwinism. Why do we need to find out about evolution? Why do we need to find out about evolution? Because it is the explanation for our existence and because it explains such a huge number of facts, because everything we know about life is explained by it. I believe in my religion so whenever I read about evolution, I can't understand it, I don't believe it, I just, like, believe my religion. Right, so you know what you believe when you start, and any new book that says anything different, you don't read it? Even if you've got evidence, I just like...I've found a stronger evidence, which is the Holy Book, so... So, the reason you believe it is because that's the one you were told first? 'I can see that a few hours in the science lab is no match 'for a lifetime of religious indoctrination.' I was brought up to believe it. Is that a good reason to believe something? Yeah, because I went to church since I was little. Yeah, and it says it in the Bible. Yes, but in the Hindu sacred scriptures, it says something different, doesn't it? Yeah, they're brought up to believe that... So everybody should believe what they're brought up to believe even though they contradict each other? You can be made to believe something in science, and then, you can be made to believe something in religious studies, but it's really up to you what you believe. You can't just say that... Well, look, I hate this phrase, "made to believe", that's awful, and I would hate anybody to think I was trying to make anybody believe anything. I'm asking you to look at the evidence. Perhaps you haven't got a full impression of how strong the evidence actually is. Nobody has seen evolution take place over a long period, but they've seen the after effects, and the after effects are massively supported. It's like a case in a court of law where nobody can stand up and say, "I saw the murder happen", but yet, you've got millions and millions of pieces of evidence which no reasonable person could possibly dispute. That's sort of the way it is. 'There's only one thing for it - 'I'm going to show them evidence - 'something they can touch with their own hands, see with their own eyes. 'Later, we'll see if I can make them think again. 'When Charles Darwin was a teenager, 'he would have been as much of a creationist 'as some of these children.' Darwin was born into a prosperous Shropshire family in 1809. His father was a doctor, and keen that his son should follow in his scientific footsteps. But the adolescent Charles, more interested in shooting and fishing than academic prowess, was contemplating an easy life as a country parson. Luckily for him, and for us, he had the opportunity to open his eyes to see the world. In 1831, as a young man of 22, Darwin's family connections got him a once-in-a-lifetime invitation - a round-the-world voyage on the survey ship, HMS Beagle. Over five years, Darwin collected hundreds and hundreds of specimens to send back to the collections. But increasingly, he wasn't satisfied with just recording the animals and plants he saw. He was beginning to have doubts about the Biblical story of how animals were created. While ashore, riding across the South American flatlands, Darwin amused himself by chasing after rheas - shy, ostrich-like flightless birds. But he was puzzled. Why had God bothered to create two very similar but slightly different types of rhea? Had an original group of rhea split in two, and once separated, started to develop in their own way? The mystery deepened when Darwin noticed an even more marked effect - on islands. I was lucky enough to retread Darwin's footsteps on the Galapagos Islands last year. Here, he began to wonder why God would have created distinctive kinds of tortoise, finch or iguana on more or less identical small islands. Were iguanas like these related rather than separately created? Were they cousins of the similar but different iguanas on nearby islands? This pattern of relationships became even more intriguing when Darwin encountered fossils. The evidence of fossils would help Darwin develop a theory of life on Earth far more wonderful and more moving than any religious story of creation. This team of American scientists has uncovered the remains of two-million-year-old ground sloths. Today, I'm joining the dig because it was fossils like these that made a huge impression on the young Charles Darwin during his voyage on HMS Beagle. To Darwin, they looked like ancient, giant versions of animals he saw around him. (MAN) The ground sloths flourished for millions of years, and were quite successful. - They were huge, weren't they? - Some of them were. They were bear-sized, up to...almost rivalling mammoths and mastodons, up to six metres in height when they reared up onto their hind legs. (DAWKINS) What struck Darwin was how, apart from their enormous size, the fossils closely resembled in every other detail the skeletons of modern sloths living nearby. (MAN) You can see similarities in the details of their teeth, peculiar features that they share with modern armadillos, modern tree sloths and modern anteaters. We can infer that they are related to these animals. (DAWKINS) The discovery of fossils was a huge challenge to the religious orthodoxy of Darwin's youth. What were these animals? When had they lived? And why didn't they exist any more? Some suggested that fossils were just God playfully ornamenting his world. Others claimed they were the bones of sinners drowned in Noah's flood. But Darwin was one of the first scientists to correctly identify them as long-dead species of animals. He was starting to grasp that the Earth might be a lot older than the Bible led us to believe. And how had he realised this? Through a fascination with geology. During the voyage of the Beagle, Darwin had had time to immerse himself in the pioneering work of Charles Lyell. Lyell argued that the landscape we saw around us was formed by the slow action of vast forces, not thousands, but millions of years of gradual change. So, if the Earth was shaped and reshaped over an immense period of time, was there room, Darwin began to wonder, for life to undergo slow changes as well? You know how old these rocks are? They're about 200 million years old. Back in the 19th century, lots and lots of people came here to look for fossils. And some of the most famous fossils have been found here. 'I'm taking the science class I met earlier to the beach. 'Many of these teenagers have been brought up 'to mistrust the idea of evolution. 'I'm hoping they'll find a small fragment of the kind of evidence 'that made Charles Darwin think again.' Do you know what our ancestors were like 200 million years ago? - They weren't... - They were around, they wouldn't have been here because this would have been the bottom of the sea. They would have been kind of like shrews, little whiskery, twitchy... It seems to be like a dream, but it's real. Yeah, yes, it does, doesn't it? This is all sedimentary rock, meaning it's laid down at the bottom of the sea, mud coming down, layer after layer after layer - that's what fossils are. 'On a beach like this, 'the pounding sea gradually exposes different layers of rock 'and within them, hidden treasure - 'a history of past life on Earth. 'So, each layer you go down to, 'you find a completely different set of animals.' And if you look at the animals that you find, and plants, over the great span of time, you find that they form a kind of ordered sequence, you find fish, 400 million years ago, but you find no mammals at all 400 million years ago. The fish gradually changed into amphibians, changed into reptiles, reptiles changed into birds, changed into mammals. Did you find that? - Yes. - Oh, that's terrific. That's really great. Yeah. That's a beautiful ammonite. That's really beautiful. Well done for finding that. That's wonderful. 'The fossil hunt has been a success. 'Like Darwin, these teenagers have been brought face to face 'with some tangible remnants of evolution.' The evidence Darwin had seen with his own eyes on the voyage of the Beagle seeded huge heretical questions in his mind. And once he started thinking, he couldn't stop. Darwin, once an easily distracted student, returned from the voyage of the Beagle a determined, even obsessive research scientist. The trip had changed him and it was soon to change the world forever. Back in London in the late 1830s, the specimens he'd collected and his reporting of the voyage made Darwin a scientific celebrity. Even more importantly, while cataloguing his finds, Darwin realised that life forms weren't fixed. They had changed over time. They must have evolved. Now, he wanted to pull together all the evidence to understand how and why this had happened. It took Darwin 20 years of research, on and off, to develop the ideas that would eventually be set out in The Origin Of Species. He wanted to be fully certain of his facts. BIRDS TWITTER The hard graft was done here at Darwin's home, Down House in Kent. Long before the days of the internet, of course, Darwin drew upon the collective knowledge of an entire generation of naturalists all over the world. He sent out thousands of letters asking for data, posing questions, trying out theories. And back the letters flowed from all around the world into Down House, a river of information. Darwin studied the detail of how different mammals share remarkably similar skeletons. Their limbs have the same bones in the same order, just reshaped and resized to suit different ways of life. He was drawn to the similarity of early embryo development in very different types of animals - fish, birds, reptiles. Increasingly, he became convinced that every living thing must be related to every other. Darwin began to see the history of life as a vast family tree. Life began millions of years ago at the base of the tree, and as time went by, our ancestors evolved, split off and multiplied along branches until now, every species on the planet is a twig at the end of a branch - all are related, all cousins. Life had evolved from single cells into complex sophisticated beings. It may seem like a huge leap, but Darwin realised it had been achieved by small steps over a vast span of time. He grasped the immense age of the Earth. Darwin believed the world was hundreds of millions of years old. Today, we know it's over four billion years old, and the life we can actually see around us has existed for an insignificant blink of that time. Darwin's wife Emma used to play to him on the piano in this very room, and Darwin would lie on the sofa and listen. It's not clear how much he got out of it, though, because it was once said of him he was so tone deaf that people had to nudge him to stand up when they were playing God Save The Queen. I want to use this piano to illustrate the vastness of geological time, and yet how comparatively little of it is occupied by those animals and plants that we know anything about. If we have the origin of life at the bottom of the piano there, and recent times at the top, I find it astonishing that we have nothing but bacteria all the way up here, past middle C, way up to about here, when more complicated cells than bacteria first evolve. And then we get the first mini-celled animals, the first large animals somewhere here, fish start around here, the dinosaurs don't come in until about here, and then, the extinction of the dinosaurs around here. About here, the apes and monkeys, and the whole of human history would occupy a space less than the width of one piano STRING right at the top of the keyboard. Life had evolved over time. But how had this happened? Why hadn't creatures stayed the same? WINGS FLAP, PIGEONS COO Darwin wasn't just an abstract theorist, he like to get his hands dirty, testing his ideas, and in the 1850s, he became fascinated by pigeons, by how man had remoulded the wild rock dove into a rich variety of forms. Darwin's bird specimens are now stored at the Natural History Museum at Tring. It's a very weird feeling, these are actually Darwin's own specimens. I see from Darwin's own label here that this is a blue owl pigeon. Tumblers are characterised by this curious tumbling behaviour that they show, sort of falling through the sky. This one has been relabelled, it is a Darwin specimen. This one actually has Darwin's original label here. Darwin realised that, for centuries, through small steps, pigeon breeders had been in the business of evolution. Here was life in constant flux. One of the big things Darwin had to fight against was the feeling that people had that species were species and they never changed into anything else. Artificial selection on dogs, pigeons, cabbages, was a beautiful illustration for Darwin of how plastic things were, you could pull them, it was like modelling clay, almost - you could take a wild animal and pull bits out, press other bits in, enlarge bits. It was showing that there's nothing static about species. Species can change. Now, in his 40s, Darwin became a pigeon fancier. He kept some 90 birds of 16 types, devoured books on breeding and attended numerous pigeon shows. What excited Darwin was the powerful comparison that could be drawn between domestic breeding and what he'd observed of nature acting on wild animals like the finches he'd collected in Galapagos. In the pigeon's case, it's artificial selection, it's human breeders using their eye to choose - I think I'll breed from that one, I want the beak longer, or shorter, I want the plumage to be whiter or fluffier. So, breed from the one that has the quality you want, and then, after surprisingly few generations, you can produce a change in the breed. In nature, it's not like that, of course. Nobody comes along and says, "I want one that has a great big, thick beak." Nevertheless, given that there are tough seeds that only a thick beak can crack, natural selection favours those individual birds that succeed in cracking the seeds, until you end up with this sort of climax beak, which is really huge, the product of tens of thousands of generations of... natural selection breeding for ability to open tough seeds. BARKING Man had utterly transformed many animals and plants by selecting for particular characteristics over and over again. Nature was also doing this. But how could nature make specific choices, as humans could? Darwin's answer would come in understanding exactly what nature is. 150 years ago, Charles Darwin's work revolutionised the way we understand our world. For 20 years, he had pieced together evidence that proved the fact of evolution and developed a theory of how nature, not God, selects life in a similar way to humans breeding pigeons. How does nature select? In the cruellest way. Today, much of the world is controlled and cultivated by man, but there are still a few remote places red in tooth and claw. I've come to Kenya, where I was born. It's one of the wilder places on Earth, where the full force of natural selection can still be seen. As night falls, it's kill, or be killed. ANIMALS GRUNT The total amount of suffering in the natural world is beyond all decent contemplation. During the minute that it takes me to say these words, thousands of animals are running for their lives, whimpering with fear, feeling teeth sink into their throats. Thousands are dying from starvation or disease or feeling a parasite rasping away from within. There is no central authority, no safety net. For most animals, the reality of life is struggling, suffering, and death. For Darwin, grappling with nature's horrors must have been a huge challenge. As a young man, he had wanted to become a country parson. He had believed in an orderly and harmonious animal kingdom. Now, he contemplated the brutal reality of nature. Darwin's brilliance was to connect what he was seeing with an idea from a completely different discipline - economics. Thomas Malthus had written a popular influential diatribe about the perils of population growth in early industrial Britain, and how this would inevitably be stopped by food shortage and disease. Darwin seized upon Malthus's warning about a human struggle for resources, and he applied it to what was happening in nature. As more individuals are produced than can possibly survive, there must in every case be a struggle for existence. Nature is an arena of pressure. Of every individual born, the chance of it surviving to reproduce the next generation is very, very small. Most animals die young. The next step for Darwin was to realise this - what makes the difference between success and failure in the struggle for existence isn't just chance. All living things vary, even if only slightly. Darwin realised this was the key, a tiny variation - sharper teeth or faster legs, keener eyes, better camouflage, better sense of smell can make a crucial difference in an animals chances of survival. If an animal survives, it is more likely to reproduce and crucially, pass those variations on to its offspring. Nature's struggle for existence means that organisms with helpful variations tend on average to survive and reproduce. Those without die without offspring. The race is survival. The finishing line is reproduction. This is what Darwin defined as natural selection... ..the key to evolution. "Natural selection is daily and hourly scrutinising throughout the world "every variation, even the slightest, "rejecting that which is bad, "preserving and adding up all that is good, "silently and insensibly working. "We see nothing of these slow changes in progress, "until the hand of time has marked the lapse of ages." Gradually, very gradually, as successful variations are inherited, natural selection sculpts life into different shapes, better and better adapted to eke resources out of their particular surroundings. Longer necks are favoured to feed from tall trees. Thinner fur for warmer climates. Life forms become ever more specialised. And if separated from their ancestral group by geography, by a forest or desert, on an island, they can specialise to such an extent that they no longer breed successfully with that ancestral group. They are then classified as a distinct species. This is the origin of species. But evolution doesn't stop there. These species are then themselves honed by the presence of other species. The environment in the form of lions is getting systematically worse from the point of view of a zebra. And from the point of view of a lion, zebras are getting systematically worse, they're getting better at running away. Predators are getting better at catching prey. Prey are getting better at escaping from predators. So there's a kind of escalation, it's an arms race. Arms races account for the spectacularly advanced engineering of life - camouflage systems, camera lens eyes, venomous stings. Arms races can be seen in unexpected places. Mankind is certainly not immune to the nightmare Darwin called, "the war of nature." We humans are currently in a battle with viruses. It's being fought all round our world. Today, in the slums of Nairobi, natural selection acts through a virulent disease cutting through the population. Nairobi's prostitutes have, on average, seven to ten clients per day with a high prevalence of HIV which causes AIDS. But genetic researchers have found that some lucky individuals have a weapon in the arms race with HIV... Salome? Yeah. > How are you? I'm Richard. '..a remarkable resistance to the virus.' Can I ask, how long have you been a sex worker? 25 years. And during that time, have you lost many friends to AIDS? I have lost many friends. Many friends? When did you first discover that you are resistant to HIV? She knew for a long time, but she actually believed completely in 1990 that she was resistant. She feels God has been good to her and she's the lucky one. Yes. It's not God at work here in all this squalor and suffering. And it's not luck either. The Canadian scientist, Larry Gelmon, has studied the odds of survival. We knew the prevalence of HIV in the sex worker population, we knew the prevalence in the clients they were dealing with, we knew how often they were having sex with these people, and it was a mathematical impossibility that they should have been sex workers for as long as they have with the number of contacts they had, and not become HIV infected. The resistance these women have seems to be a variation that can be passed on to their children. Some of the women are related to each other familially, we also think there is some factor in their blood, in their cells that is probably genetically transmitted. (DAWKINS) I suppose if we came back in 1,000 years, we might expect to see a major shift in the frequency of these genes in the population? (GELMON) Yes, I think in any epidemic situation, those people who are very vulnerable and susceptible will get sick and die. And those people who are going to survive are going to have some kind of resistance which they'll transmit on to their descendants. Just as Europeans today are descendents of those who had the genes to survive the plague, so if Africa's AIDS epidemic took its course, natural selection would favour descendents of women with resistance to HIV. This is the unstoppable force of natural selection first revealed by Darwin, now observed by modern science. Back in England at Down House, now 20 years after his voyage on the Beagle, Darwin had worked out the answers to the biggest questions ever asked. But he was strangely reluctant to go public with his idea. Darwin himself said that he'd become a kind of machine for grinding theories out of huge assemblages of facts. I think that wasn't really what it was like at all. He was an extraordinarily imaginative, deep thinker. He had a prodigiously curious mind as well. He was drawn to facts that didn't fit. He once said, "I cannot bear to be beaten." Darwin's theory explained how the diversity of life from the planet had evolved spontaneously without interference from any god. But he was acutely aware of how upsetting this flat contradiction of the religious story would be. He hesitated to publish. Then, in June 1858, Darwin received a letter from a naturalist travelling in the Far East, Alfred Russel Wallace, which set our similar ideas. Darwin was in despair about being scooped. He was even ready to drop his life's work. But he was persuaded by Charles Lyell and others to present his unpublished work alongside Wallace's notes, and then complete his masterpiece for publication. I've come to meet Randal Keynes, Darwin's great-great-grandson to try to understand Darwin's frame of mind as he finished his book. This is a book about geology by Mr Greenough. It has this wonderful inscription - "Charles Darwin, Buenos Aires, October 1832." So he's on the Beagle, really getting into his stride as a geologist. This is a scrapbook, a children's scrapbook that belonged to Darwin's daughter Annie. 'Darwin was no aggressive polemicist. 'He didn't take to the stage to publicise his work, 'but sought to influence leading thinkers behind the scenes, 'by sending them proof copies of the book with apologetic letters attached.' He would write things like, "This vile rag of a theory of mine." Was that genuine modesty or was there an element of false modesty about it? It was entirely real, um, and this is a very strange point about him. Through the years when he was steeling himself for publication, um, he was, at different times, enormously confident in it, and at other times, he was utterly uncertain. He had a deep fear, I think, that one species would be discovered that had some element of its make-up that could only have been designed. Doubts may have lingered in Darwin's mind, but finally, 150 years ago, he set out his ideas on evolution and how it worked in The Origin Of Species. The book sold out its first run of 1,250 copies within two days. It has never been out of print since. The Origin turned our world upside down... ..but still there was one big gap in Darwin's understanding. 150 years ago, at the age of 50, Charles Darwin finally published the big idea he had sat on for almost 20 years... ..a natural law that explains life itself and the evidence available to him to back it up. This is the most precious book in my collection. It's a genuine first edition Origin Of Species. But it's not just the most precious book in my library. Charles Darwin's Origin Of Species is one of the most precious books in the entire library of our species. This book made it possible no longer to feel the necessity to believe in anything supernatural. It completely revolutionised the way we see ourselves, the world and our origins. But what Darwin never cracked was how the improvements of natural selection were preserved from generation to generation, why they didn't become diluted by interbreeding. It was only in the 20th century, in the neo-Darwinian revolution, that scientists married evolution with genetics. Genes are the long strings of code, instructions to the cells that build all living things. Scientists now realise that genes from the parents don't blend as they combine during reproduction. Each gene is inherited in its entirety...or not at all. The science of the genes also showed how new variations arose. When animals reproduce, their genes are copied, and put into sperm and eggs. During that copying process, occasionally there's a random mistake. Those mistakes are mutations, which give rise to new characteristics on which Darwinian natural selection then acts. And, what's more, genes can be compared with pinpoint precision. The genes in every cell of every living thing are made up of DNA - a code of the same four chemicals, known as A, T, C and G, which these machines can analyse. Whether the cell builds a hamster, a horse or a human simply depends on the order of the letters in the code. Just as Darwin might have predicted, animals more closely related by evolution have more similarities in their code than more distantly related animals. And these codes can be printed out right here in this man's lab. In 2000, Craig Venter was among the first scientists to map the human genome, our sequence of code letters. In the process, this unlocked the ultimate proof of Darwin's Tree of Life. 'He was looking at the visible world and seeing how different it was.' We now have the opportunity, with this toolset, to look at the invisible world, that he could only get hints of. And it shows that there's vast continuity from the simplest life forms to the more complex. He, of course, emphasised diversity, because that's what he saw, the whole organism, but you're finding the incredible similarity that there is between creatures. Even bacteria. To me, it's not a theory any more. I've looked at the genetic code of this wide diversity of species, and it's a continuum. Yes. Well, evolution is a fact. That's right. I mean, there's no question about that, and I'm always being asked, "Well, produce the evidence!" And, really, you're producing the best evidence of any. I mean, fossils are nice, but if we haven't got a single fossil anywhere... The genetic code on its own is enough. the evidence from this lab alone would be... Not just enough but overwhelmingly, staggeringly enough. Darwin anticipated problems with his theory. Modern science has answered them. Evolution by natural selection has been triumphantly vindicated as fact. Case closed, surely. But can I convince those school children? What's so beautiful about DNA is that it's turned biology into a kind of branch of computer science, that every animal and plant is carrying around, inside every one of its cells, an instruction book for making that animal and making its children. You've got billions of letters and you can actually line them up and you can take the rat DNA and the mouse DNA and you line them up and you say, "Same, same, same... Ah! A difference there. "..same, same, same, same... A difference there." And that means that when you say that two animals like rats and mice have a common ancestor, you can be totally confident that that's right because the sheer number of similarities is so gigantic, far, far more than Darwin could ever have dreamed of, and Darwin would just have loved to know about DNA. It's such a shame that he didn't live long enough to learn about DNA. I already believed in evolution, but this has just helped me to understand a bit more about it. We have talked about it in class more, but I still do believe in God. But I'm starting to think whether evolution is true or false. I do believe in evolution but I don't think it's ever going to be 100% accepted because there are many religious people out there. I thought about it more but I still believe in what the Bible tells me. When Richard came to our school today, I started learning about evolution and I'd really love to learn more about it but I don't want to, like, leave my religion and go down that path. I think evolution is the main part of how the Earth developed, but I'll still say my prayers and just keep life going. I only had a few hours with these children, but I hope it'll help them begin to open their eyes to the wonderful reality of life and, at the very least, ask questions about what they've been brought up to believe. Darwin used to do a lot of his thinking on solitary walks along this path around his home, Down House. At the end of Origin Of Species, he contemplated how an entangled bank along a lane like this, with its teeming life of plants, birds, worms and insects, had been formed by the unseen laws acting around us. "There is grandeur in this view of life. "Whilst this planet has gone cycling on "according to the fixed law of gravity, "from so simple a beginning "endless forms most beautiful "and most wonderful "have been, and are being, evolved." Thanks to Darwin, we, alone of all species, know that each and every one of us is a thread in the evolved fabric of life. Darwin showed us that the world is beautiful and inspiring without a god. He revealed to us the glory of life and opened our eyes to who we really are and where we've come from. In the next programme, Darwinism applied to mankind and our society, its terrible misuse in attempts to justify cut-throat competition, even genocide. In the world of the selfish gene, what hope for the human species?