Darwin Now PDF

‘A MAN WHO DARES TO WASTE ONE HOUR OF TIME HAS NOT DISCOVERED THE VALUE OF LIFE’ Charles Darwin Throughout the19th One man, and one book, came to symbolise the new biology of evolution. century there was a Charles Darwin, born in 1809, was 50 transfo...

‘A MAN WHO DARES TO WASTE ONE HOUR OF TIME HAS NOT DISCOVERED THE VALUE OF LIFE’ Charles Darwin Throughout the19th One man, and one book, came to symbolise the new biology of evolution. century there was a Charles Darwin, born in 1809, was 50 transformation in thought when he published perhaps the most famous scientific work ever written. that still reverberates Therefore, 2009 marks both the today. The workings of bicentenary of his birth and 150 years since the first appearance of nature and the variety On the Origin of Species by Means of life were re-imagined of Natural Selection. in ways that underlie This exhibition explores the origins of all modern biology. Darwin’s book, outlines his central ideas, and explains how they remain The wider implications at the core of contemporary research of these ideas still in biology and medicine. provoke controversy. 1 1 WHO WAS DARWIN? Charles Darwin was the son of a prosperous country doctor in Shrewsbury, in the largely rural English county of Shropshire. As a boy he loved the countryside and its creatures but had trouble settling on a career. He abandoned medical school in Edinburgh, and was sent to Cambridge University to prepare for life as a vicar. At university Darwin met some of the For the rest of his life he continued most brilliant naturalists of the day and working – to defend his theory and to in 1831 he acquired a berth on the understand its implications, and he naval survey vessel HMS Beagle for a published further books – on orchids, world voyage. During the five-year earthworms and the expression of journey Darwin kept a scientific field emotions, among others. journal, covering biology, geology and anthropology, with detailed notes and Darwin became a reclusive, semi- observations on the indigenous invalid in middle age and died in 1882, animals, plants, birds and insects of the but there was one constant throughout places he visited – Brazil, Chile, Peru, his life – a boundless curiosity about the Galapagos Archipelago, Tahiti, New the natural world. Zealand and Australia, among others. Back in London, and later at his new home at Down House in Kent, he gradually came to understand how individual species could change; how evolution could work – although it took him over 20 years to feel ready to Ink and watercolour drawing of Charles Darwin in 1840 by George Richmond. publish his ideas. © English Heritage Photo Library. 2 3  Exquisite adaptations ‘How have all these exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one distinct organic being to another being, been perfected? We see these beautiful co-adaptations most plainly in the woodpecker and mistletoe, and only a little less plainly in the humblest parasite, which clings to the hairs of a quadruped or feathers of a bird, in the structure of a beetle, which dives through the water, in the plumed seed, which is wafted by the gentlest breeze. In short, we see beautiful adaptations everywhere.’ The Origin of Species, chapter 3. Although the title of his book referred This was the first book to outline a to the origin of species, these words theory of transmutation of species. of Darwin show how he was also Darwin was also informed and preoccupied with the harmonisation influenced by the new geology of of organisms and their surroundings. Charles Lyell (1797 to1875), who argued that rock formations had been His approach to explaining how these produced by gradual change over ‘exquisite adaptations’ occurred was extremely long periods of time – deeply rooted in contemporary hundreds of millions of years. scientific thought, beginning with the evolutionary speculation of his Against this new backdrop of deep grandfather, the doctor, poet and geological time, Darwin imagined the polymath Erasmus Darwin (1731 working of a slow selection – with most to1802). In 1809 Philosophie creatures dying before they could Zoologique was published by Jean- reproduce, and only a few giving rise Baptiste Lamarck (1744 to1829). to offspring. John Stevens Henslow, Professor of Botany at Cambridge University, 1825–61. Henslow recommended Darwin for the job as naturalist on HMS Beagle. Background: Belize rainforest. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online © Nigel Tucker. (http://darwin-online.org.uk). 4 5  ARCTIC ARCTIC OCEAN OCEAN Arctic Circle Plymouth Azores PACIFIC ATLANTIC PACIFIC OCEAN OCEAN Tenerife OCEAN Tropic of Cancer Tropic of Cancer Cape Verde Galapagos Equator Equator INDIAN Equator OCEAN Cocos (Keeling) Islands Callao/Lima Bahia Mauritius Rio de Janeiro Tropic of Capricorn Tropic of Capricorn Tropic of Capricorn Valparaiso Montevideo Sydney Cape Town King George’s Sound Bay of Islands Hobart Falkland Islands 0 1000 Km Map of Darwin’s voyage on HMS Beagle. 6 7 2 GLOBAL NETWORKS Darwin did not travel again after his Beagle voyage. However, throughout his life, he was a prolific letter-writer. It was his way of cementing scientific friendships, pursuing collaboration and gathering observations. After publishing On the Origin of Species by Means of Natural Selection Darwin became renowned and autograph collectors wrote to request his signature. Preoccupied with ‘the species Once he had an outline of his theory, © George Beccaloni. question’ Darwin was convinced that he consulted diplomats, army officers different species could start by one and colonial officials, gardeners, earlier variety changing into another – horse-breeders, farmers, fur-trappers by transmutation. But how? and zookeepers, as well as botanists and naturalists. He studied specimens, the exhibits in museums and zoos, and the work of Letters also kept him in touch with the animal and plant breeders. And he travelling naturalist Alfred Russel read – geology, natural history, Wallace, who had formulated similar and philosophy. ideas. It was a paper from Wallace that finally induced Darwin to publish As he studied, he corresponded his theory. with colleagues around the world – Brazil, India, China, North America, Once The Origin of Species by Means South America, New Zealand and of Natural Selection appeared, in 1859, Jamaica – outlining his ideas, arguing the letter writing brought new his hypothesis and requesting information for updates of the work, information and new specimens. and for new projects. It also helped to influence the reception of his radical ideas. The sand walk or ‘thinking path’ at Down House, photographed around 1909. Darwin walked here every day when he was at Down and used the time to contemplate his observations and to develop his theories. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online (http://darwin-online.org.uk). 8 9  A life in letters ‘I am now employed on a large volume describing the anatomy and all the species of barnacles from all over the world. I do not know if you live near the sea, but if so I should be very glad if you would collect for me any that adhere (small or large) to the coast rocks or to shells or to corals thrown up by the gales, and send them to me.’ Darwin’s letter to his former servant on HMS Beagle, Syms Covington, in Australia. The Darwin Correspondence Project correspondents around the world. in Cambridge has collected 15,000 of By the end of his life, in 1882, Darwin Darwin’s letters, involving around 2,000 was a member of 57 foreign learned correspondents around the world. societies – memberships he maintained without ever leaving the country after By the time he published The Descent HMS Beagle docked in Falmouth of Man, and Selection in Relation to Sex in 1836. in 1871, Darwin was writing around 1,500 letters a year. In fact, by then, One of Darwin’s projects was a much of his day revolved around comprehensive study of barnacles. reading and writing letters – he even Begun as a diversion from his study put a mirror next to his study window of species, it grew into an eight-year Darwin spent eight years studying barnacles and Alfred Russel Wallace (1823–1913), who famously so that he could see the postman exploration recorded in three made a major contribution to our understanding put forward similar ideas on the origin of species walking up to the house each day. immensely detailed books. Using his of them. as Darwin. A paper by Wallace was presented skills of persuasion, or appealing to Reproduced with permission from John van Wyhe, ed., alongside some of Darwin’s work at the Linnean A third of the surviving letters can shared curiosity, he wrote to those The Complete Work of Charles Darwin Online Society in 1858. now be read and searched online at who had an interest in barnacles, and (http://darwin-online.org.uk). © Wellcome Library, London. www.darwinproject.ac.uk. The entire others who had been recommended collection is also being published in by colleagues. book form, in a series expected to total 30 volumes when complete. Darwin requested information, specimens – preferably live ones – The letters reveal how substantially and, in some cases, the loan of their Darwin’s success in advancing a new entire collections. Darwin dissected vision of the natural world depended and catalogued every specimen, on others: his wife, Emma, their ten creating the definitive work on these children at home in Kent, his friends small crustaceans. and colleagues in England and his Fancy pigeon breeds similar to those studied by Darwin’s study at Down House shortly after his Darwin as he developed his theories of evolution death in 1882. Copper engraving by Acel H. Haig. and natural selection. Darwin compared ‘artificial Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online selection’ used by breeders to that which could (http://darwin-online.org.uk). Background: Acorn barnacle (Semibalanus balanoides). be seen in nature – ‘natural selection’. © David and Katie Urry/www.ardea.com. © Natural History Museum, London. 10 11 3 The variations, and their effects, can be very small. Repeat the cycle thousands of times, and the results can be dramatic. DARWIN’S THEORY – In summary: all you need for evolution is inheritance, variation, and selection. INHERITANCE, In The Origin of Species Darwin laid out an abundance of evidence for evolution. But there were gaps in the story. One, which is still not easily VARIATION, Illustration from the first edition of On the understood, was the origin of life. Origin of Species by Means of Natural Selection Another was that he had no convincing depicting the evidence that different species with ideas about how variations in shared characteristics can be explained through characteristics were passed down SELECTION common ancestors. the generations. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online More recent science has supplied (http://darwin-online.org.uk). some details about the mechanism of inheritance. Every creature can be defined by the information in its genes. One reason that Darwin’s ideas have endured is These are messages written in the their simplicity. The theory of evolution by natural sequence of chemical letters in the DNA molecule. selection has just three essential parts: Genes are copied and passed on When individuals in a population reproduce, to each creature’s offspring. But the process of copying can introduce the new generation must resemble their parents. small mistakes, which produce random changes in the DNA information. These The resemblance between generations must be are the mutations that lead to variation in the population. close, but not perfect, so that each generation includes new variations in characteristics. Some mutations bring advantages, which make reproduction more likely in a particular environment. So, again, we There must be a link between some of these new have inheritance, variation and selection, variations and the chances that an individual will but this time among molecules. Diagrams of pigeon skulls showing how be better able to survive and reproduce. domestication and selection led to variations within one species. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online (http://darwin-online.org.uk). 12 13  Evolution by selection ’Can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable variations and the rejection of injurious variations I call Natural Selection.’ The Origin of Species, chapter 4. Darwin’s work was concerned with Beyond that, entire universes might the existence and evolution of living be subject to natural selection, creatures. His discovery that according to cosmologist Lee Smolin. inheritance, variation and selection He speculates that they ‘reproduce’ can lead to change in species, when an existing universe collapses however, has far wider applications. into a black hole, and a new one is born in which the laws of physics In fact, provided a population of are subtly different. individual entities passes through a number of generations in some kind There are also more earthbound of cycle, evolution can occur. examples of the idea of selection, such as its application to ‘evolve’ computer Looked at this way, natural selection programs known as genetic algorithms applies to life on Earth, as Darwin and in systematic search for new argues. Theorists and experimenters molecules that may find use as drugs. studying the origin of life assume it applies to populations of molecules Consider how the selection theory in proto-living systems. Exobiologists model can be applied to our (who study organisms that originate understanding of language change, from outside Earth) argue that it should cultural trends and technological also apply to life anywhere in the developments, and one can understand universe, even if the molecules in play why US philosopher Daniel Dennett turn out to be different from those we described evolution by selection as ‘the observe on Earth. single best idea anyone has ever had’. Opposite page: Page from Darwin’s species notebooks. Written between 1837–38, his notes outline his ideas on the ‘transmutation of species’. Reproduced by kind permission of the Syndics of Cambridge University Library. Background: Cover from the first edition of On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life, published by John Murray in 1859. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online (http://darwin-online.org.uk). 14 15 4 ‘The most important original observations, recorded in the volume of 1859 are, in our estimation, its real gems – few indeed and far apart, and REACTIONS leaving the determination of the origin of species very nearly where the author found it.’ Sir Richard Owen, naturalist ‘What can we believe but that Darwin’s Darwin’s readers had strong opinions about his book theory is an ingenious and plausible in its early years – but in very different ways. speculation, to which future physiologists will look back with the kind of admiration we bestow on the ‘How extremely stupid not to have atoms of Lucretius, or the crystal thought of that!’ spheres of Eudoxus, containing like Thomas Huxley, naturalist these some faint half-truths, marking at once the ignorance of the age and the ‘He has opened a path of inquiry full ability of the philosopher.’ of promise, the results of which none Henry Charles Fleeming Jenkin, can foresee.’ engineer John Stuart Mill, philosopher ‘I have read your book with more pain ‘One of the most interesting parts of than pleasure. Parts of it I admired Sir Richard Owen (1804–92). Mr Darwin’s volume is that in which he greatly; parts I laughed at till my sides © Natural History Museum, London. establishes this law of natural selection; were almost sore; other parts I read we say establishes, because – with absolute sorrow, because I think repeating, that we differ from him them utterly false and grievously totally in the limits which he would mischievous.’ assign to its action – we have no doubt Adam Sedgwick, geologist of the existence or of the importance of the law itself.’ ‘We had a capital meeting at Norwich, Bishop Samuel Wilberforce and dear old Hooker came out in great force as he always does in ‘It is remarkable how Darwin emergencies. The only fault was the rediscovers, among the beasts and the terrible Darwinismus, which spread plants, the society of England with its over the section and crept out when division of labour, competition, opening you least expected it, even in Contemporary cartoon of Thomas Henry Huxley of new markets, “inventions” and Fergusson’s lecture on “Buddhist (1825–95). Malthusian “struggle for existence”.’ temples”. You will have the rare © Natural History Museum, London. Karl Marx, political theorist happiness to see your ideas triumphant during your lifetime.’ Adam Sedgwick (1785–1873). Thomas Huxley, naturalist © Wellcome Library, London. 16 17  Critics and supporters Some people were simply unaware of Some defined the theory as reinforcing Darwin’s theory. When he and his fellow support for Europeans’ imperial evolutionary theorist Alfred Russel ambitions, and for the idea that Wallace had their first papers read at different races, or nations, competed the Linnean Society in 1858, the for ascendancy. Some saw the reaction was muted. The President of theory as a basis for what the British the Society said later that the year had philosopher Herbert Spencer called not been marked by any remarkable social Darwinism, in which the class discoveries. structure was a result of – in his famous phrase – ‘survival of the fittest’. In this When Darwin’s book was published the view, economic competition mirrored following year, responses were varied. the struggle for survival in the Some of Darwin’s strongest supporters, natural world. such as Thomas Huxley, still took issue with many details of the theory. Many However, the idea of evolution was accepted the idea of evolution but not embraced by some political radicals, the mechanism he proposed. Some who found the picture of change it thought natural selection explained offered a basis for their hopes for some cases of adaptation, but not revolution in the social order. Henry Charles Fleeming Jenkin (1833–85). others. There was much speculation © Wellcome Library, London. about the duration of natural selection, All these interpretations of Darwin’s and the length of time necessary for and Wallace’s ideas were argued species to change. over and criticised in the numerous periodicals of the time. They were Some religious commentators had often caricatured and made fun of in little difficulty with Darwin’s approach cartoons, humorous essays, or music to the variety of life, which could still hall songs. accommodate a creator. A lawful universe was, in their view, still an Generally, Darwin’s book, therefore, orderly realm ordained by God. was one that people tended to read But some believers felt Darwin’s selectively – focusing on whatever ideas presented a challenge to ideas and conclusions they found concepts of morality and aspects of favour with and rejecting those they their interpretation of religious texts. had no sympathy for. Lithograph of Karl Marx (1818–83). © Wellcome Library, London. Background: Illustration of sea anemone from Ernst Haeckel’s Kunstformen der Natur, 1899. Bishop Samuel Wilberforce (1805–73). © Humboldt-Univerisät zu Berlin/The Bridgeman Art Library. © Julia Margaret Cameron, Wellcome Library, London. 18 19 5 EVIDENCE FOR EVOLUTION – THEN The Origin of Species persuaded many readers that evolution occurs because Darwin expounded the arguments for and against with such thoroughness. He also presented them with a vast amount of varying types of evidence. Darwin laid out the enormous diversity There was also another line of of living things. He described the evidence, which was close to Darwin’s equally impressive variation within heart because it recalled things he had single species, brought about by seen with his own eyes on his youthful people controlling the breeding of travels. The distribution of species of dogs, horses, pigeons or cattle. He also many kinds, in many lands, fitted his related the slow appearance – and new view of the long history of the disappearance – of species in the Earth and the power of variation to record left by fossils in the rocks. create slow changes in living forms. The critical evidence came from close Particularly important here was the comparisons. Comparing fossils from life of islands, such as the Galapagos different periods showed gradual Archipelago. Species found in the change over time. Comparing body same kind of environments on the plans and bone structures of different mainland that could have flourished living species showed how they were on islands were often absent – this related to one another by common suggested that the species that live descent. Comparing growing embryos on islands were not created there, but showed how apparently different had somehow, in the past, managed to The Madagascar star orchid (Angraecum sesquipedale) has a nectar tube of 25–30cm. Darwin species looked much more alike colonise the islands from the mainland. theorised that a pollinator moth must exist with a proboscis long enough to reach the nectar. when they were at the earliest stages The hawk moth was identified over 40 years after Darwin’s death. of development. © Peter Whitehead and Colin Keates, Natural History Museum, London. 20 21  A new way of looking ‘Several classes of facts... seem to me to proclaim so plainly, that the innumerable species, genera, and families of organic beings, with which this world is peopled, have all descended, each within its own class or group, from common parents, and have all been modified in the course of descent.’ The Origin of Species, chapter 13. Darwin described The Origin of Species ‘Look closer at the details,’ Darwin as ‘one long argument’. The argument urged, ‘and see that the flora and fauna was in support of the idea of descent of any particular island are related to with modification. His close study of those of the nearest mainland, but are the way breeders could modify species slightly different.’ He even identified a – such as pigeons – helped him relation between the depth of the sea develop his theory and he supported it between islands inhabited by mammals with other evidence drawn from both and the degree of similarity between his and other people’s observations. the species on the different islands. His experience on the Beagle voyage All this suggested that the variations in encouraged him to consider the species depended on how long they Illustration of the jawbone of the ground sloth Rare fossil of the ‘dinobird’ (Archaeopteryx distribution of species – what we now had been separated. The longer they (Mylodon darwinii). When he was in Brazil, Darwin lithographica), the earliest and most primitive call biogeography. This was also a had lived apart, the greater the chance discovered a fossil of the ground sloth – which form of bird known. In 1868, Thomas Huxley, special interest of Alfred Russel that they would have changed in ways became extinct about 10,000 years ago. ‘Darwin’s Bulldog’, was the first to suggest Wallace, during his own journeys as that distinguished them from a © Natural History Museum, London. that birds evolved from dinosaurs. a naturalist. common ancestor. © Natural History Museum, London. Darwin and Wallace were both Added to this was much geological fascinated by islands. Sometimes evidence and documentation, from the islands were so far from the mainland study of fossils, and from natural that certain groups of species were history. All were woven into a new completely absent. For example, concept: how to recognise in the living oceanic islands had no frogs, toads world, the traces of its long history. or newts. Illustration of a Darwin hawk moth (Xanthopan Pillbox containing fossils collected by Darwin morganii praedicta) feeding from a Madagascar during his travels on HMS Beagle. Star orchid (Angraecum sesquipedale). © Sedgwick Museum of Earth Sciences, University of Cambridge. Reproduced with permission. © Illustration by Emily Damstra. Courtesy of the Smithsonian Institution. Background: Close up of the centre of an ammonite. © Helen Cowdy, Natural History Museum, London. 22 23 6 Zebrafish (Danio rerio) are now also used as a model organism by geneticists to test their theories of inheritance and gene function. © Wellcome Library, London. EVIDENCE FOR EVOLUTION – NOW ‘When we regard every production of nature as one Darwin gathered a mass of information The longer the time since two species to support his ideas. The types of had a common ancestor, the more which has had a history; when we contemplate every evidence he used – from fossils to numerous the small differences in their complex structure and instinct as the summing up distribution of species – are all much genes will be. So the human version more developed 150 years later. of a gene will be more like the of many contrivances, each useful to the possessor, The proliferation of living forms in the chimpanzee version than that of a nearly in the same way as when we look at any so-called Cambrian explosion around mouse or a fish; the mouse version 530 million years ago, for example, will be more like that of a rat. great mechanical invention as the summing up of has been studied in enormous detail. the labour, the experience, the reason, and even These traces of past change can now But there is even more impressive be mapped in detail; furthermore, the blunders of numerous workmen; when we thus evidence for evolution from recent evolution is still in evidence today. view each organic being, how far more interesting, biological discoveries, which Darwin had no knowledge of. Much of it comes The spread of bacteria that can resist I speak from experience, will the study of natural from studying deoxyribonucleic acid antibiotics is a good example of history become!’ or DNA, the chemical at the heart of evolution in action. When chemicals heredity, and thus the raw material attack, bacteria that can survive the for evolution. encounter will go on to reproduce The Origin of Species, chapter 14. when the other bacteria die. Looking closely at DNA reveals new As bacteria reproduce quickly, and evidence on how different species are have other methods of spreading related. Genes for basic components genes between them, the resistance of cells have been preserved through can easily spread faster than scientists time – most variations here are can develop new antibacterial drugs. eliminated by natural selection as they are harmful. Sequencing the same gene in many species reveals a clear pattern of descent with modification. 24 25  The Galapagos finches One does not have to study bacteria When the Grants first did fieldwork in or DNA to find evidence of evolution the Galapagos in the 1970s, there were in real time. Recent observation just two species of finch on one of the of the varied species of finch that islands – Daphne Major – the medium Darwin observed on the Galapagos ground finch (Geospiza fortis) and the Archipelago – without realising how cactus finch (Geospiza scandens). significant they were – have shown In 1977, a catastrophic drought killed how strong selection can produce many plants, leaving only a limited noticeable change in a matter of years. supply of the small seeds that the birds relied on for nourishment. In the The first finches arrived in the islands ensuing competition for food, many between two and three million years of the medium ground finches died ago; those original colonists have now because their beaks did not have the evolved into 14 separate species. mechanical power to crack the larger The different species have varying seeds that remained. environmental preferences, seek different things to eat and often The result was that the next generation have beaks of dissimilar shapes. of finches on Daphne Major had larger, Wild-type fruit fly (Drosophila melanogaster) – this fly has been used since the early 20th century as a stronger beaks, inherited from the model experimental organism by geneticists. Such features can change in far survivors of the drought. © Wellcome Library, London. shorter time than three million years. The Galapagos finches have been A few years later, the selective effect studied intensively for three decades was reversed when heavy rain by biologists Peter and Rosemary encouraged growth of an unusually Grant of Princeton University. large population of small-seeded plants – and the birds with smaller beaks had the advantage. Molecular model of a short string of DNA double Four species of Galapagos finch with different helix generated from X-ray diffraction data. beaks from Darwin's Journal of Researches (1839). © Wellcome Library, London. Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk). Background: Eye of an adult fruit fly (Drosophila melanogaster) – coloured. © David Strutt, Wellcome Library, London. 26 27 7 DOES EVOLUTION CHALLENGE RELIGION? The epic sweep of the evolutionary history of life is an inspiration to many. As the British palaeontologist Simon Conway Morris put it: ‘Evolution discovers the song of creation.’ Conway Morris is a scientist and a that flow from them may appear to be However, this is only one interpretation Even without formal religious belief, Christian, and believes that each contradictory at times but, to some of a creator’s role in the cosmos. anyone who contemplates what perspective enriches the other. extent, this depends on how they Darwin’s theory of species says modern science reveals about the His commitment to Darwinism are interpreted. nothing about the first appearance diversity and intricacy of life is bound underlines his belief that there is of life – or about the origins of the to feel the power of one of the no simple opposition between Some Victorians who read Darwin’s universe. It is perfectly plausible to universal sources of spiritual feeling – science and religion. theory, for example, were offended uphold a scientific account of how a sense of wonder. because it negated the role of a natural laws allowed the universe, The idea that Darwin’s theory creator in the genesis of individual and life, to develop, and to believe contradicts religion arose because species. People who continue to that a deity created those laws. it was, in part, a scientific answer to believe that living organisms originate some questions – such as how species from specific acts of divine creation Darwin’s most tenacious supporter, the appear – that had traditionally been still, therefore, find modern versions of scientist Thomas Henry Huxley, coined resolved by religious explanations. the theory of evolution hard to accept. the word ‘agnostic’. It described his own view that, when the limits of Science and religion are both dynamic reason are reached, an open mind sets of ideas. Each venerates basic about the unanswered questions is texts. Like all books, these can be the best approach. read in different ways. The beliefs 28 29 ‘Today we are faced with a challenge that calls A sacred epic for a shift in our thinking, so that humanity stops Darwin saw no contradiction between As Simon Conway Morris said: ’Animals his idea that all forms of life evolved that are the end result of many billions threatening its life-support system. We are called from earlier species, and beliefs in a of years of prior stellar and biological to assist the Earth to heal her wounds and in the creator deity. Soon after The Origin of evolution may be the only way to allow Species was published in 1859, the at least one species to begin its process heal our own – indeed, to embrace the Anglican clergyman and novelist encounter with God.’ whole creation in all its diversity, beauty and wonder. Charles Kingsley wrote to Darwin about the book. ‘I have gradually learned,’ Others, such as the US evangelist This will happen if we see the need to revive our he said, ‘to see it as just as noble a Michael Dowd, have preached that sense of belonging to a larger family of life, with conception of deity to believe that evolution is a sacred epic, revealing a he created primal forms capable of story of complexity that unfolds over which we have shared our evolutionary process.’ self-development... as to believe that 14 billion years. he required a fresh act of intervention. Wangari Maathai, Kenyan environmental activist, awarded the Nobel Peace Prize I question whether the former be not Darwin’s notion of modification with in 2004. the loftier thought.’ descent is supported by the fine detail of similarity between many genes Darwin admired this sentiment and, shared by all species, which has been with Kingsley’s agreement, included confirmed by the human genome it in later editions of The Origin project. This emphasis on the unity of Species. of creation is a further inspiration to many. Since then, some adherents of all religions have continued to take inspiration from the richness of the natural world, which remains, for them, as wondrous after Darwin as it was before. 30 31 8 HOW DO NEW SPECIES APPEAR? Darwin offered a theory to explain how one species can change into another. That is what evolution means. Accepting his theory meant overturning the older view of species as distinct kinds, which stay the same for ever. Although it convinced biologists around the world it also prompted questions that are still being debated. One such question, vital for biologists, other ways of moving apart was how exactly does change within a biologically. Genetic changes create population lead to recognisably small differences in behaviour – such different species? as eating habits, or mating preferences – which can gradually increase. Over A possible reason is separation. When, time, these lead to divergent ways of for example, part of the population is life without physical separation. segregated – by, say, a mountain range, river or sea channel – and if the Professor Jim Mallet of University barrier is maintained for a sufficient College London has been exploring length of time, the two populations will how this can work in a series of closely change enough to become unable to related species of tropical Heliconius interbreed. That is often taken as an butterflies. Butterfly wing colours and unassailable condition for two patterns change easily. That itself does collections of similar creatures to be not lead to new species. Some of the classed as separate species. However, butterflies exude chemicals with a it is not the only one, and it does not taste that is repugnant to butterfly- always apply. eating birds. He also discovered that male butterflies have a strong Plate showing four forms of Heliconius numata, two forms of Heliconius melpomene, and the two Another possibility, which has received preference for females whose corresponding mimicking forms of Heliconius erato highlighting the diversity of patterns and mimicry in more attention in the last two or three wings match their own. As these Heliconius butterflies. decades, is that sub-populations, which characteristics interact, new species © This image was published in a Public Library of Science journal. are not physically separate, can find emerge, and they no longer interbreed. 32 33  Left: Illustration of a Galapagos mockingbird (Mimus melatonis). Variations between the Two sides of a coin mockingbirds on the Galapagos Archipelago first ‘It is important to remember that naturalists have no golden rule by which to aroused Darwin’s attention to the distribution of distinguish species and varieties; they grant some little variability to each species, species on the islands. but when they meet with a somewhat greater amount of difference between any Reproduced with permission from John van Wyhe, ed., The Complete Work of Charles Darwin Online two forms, they rank as species.’ (http://darwin-online.org.uk). The Origin of Species, chapter 9. The latest views on how new species This kind of variation could be the start arise are consistent with Darwin’s, of a long-term process. A species under argues Professor Jim Mallet. In the natural selection, as opposed to human second half of the 20th century, most influence, can develop a range of types, biologists believed that different perhaps showing different ecological species were cleanly separated and adaptations. Some of the types then differed sharply from their evolutionary acquire differences, which become so relatives. This made it harder to see well established that they can be how they came into being, unless there classed as separate species, even was a long-term physical separation though they can still produce hybrid imposed by mountains or seas. offspring occasionally. Eventually, they Below: The Galapagos Archipelago. Scientists call this allopatric speciation. may turn into creatures that are related, © Alexander Deursen. with a shared ancestor but that no Mallet believes that differences longer cross, in line with the commonly between species are continuous with used strict definition of species. variations within a species. This was also how Darwin described the All of this can happen while the situation in The Origin of Species. different varieties live alongside one He was influenced by his studies another in the same geographic region. of artificially bred varieties, such as The technical term for this is sympatric pigeons. A more familiar example would speciation. This process suggests how be dogs, which human breeders have species are still changing all around us. fashioned into many different types. As Mallet puts it: ‘Speciation is easy.’ Technically, all remain the same species – though a Chihuahua might have a The work is also important in probing problem mating with a Great Dane. the roots of biodiversity, and for planning conservation efforts. Speciation and extinction are two sides of a coin. Background: Wing scale detail from purple emperor butterfly (Apatura iris). © Stephen Dalton/www.nhpa.co.uk. 34 35 9 EVOLVING HUMANS Darwin’s theory of common descent had a startling implication: ‘Humans are not separate from the rest of nature. Yet we are also clearly different from other creatures. Evolutionary theory is a product of human culture, which is itself a mark of that difference.’ Explaining the emergence of human Human Evolutionary Studies, University consciousness and culture still of Cambridge, emphasises that challenges researchers in many fields. changes in tools can be seen in two We can now compare the complete ways. First, they may be a record of gene sequences of humans and our development and migration of groups, closest living relatives, the which used different techniques chimpanzees. This offers clues to to sculpt their flints. Second, the which changes in DNA were crucial in differences may have more to do with producing prominent human traits. Our responses of groups with similar skills enlarged brains, upright walking, and to different environments, or to the use of language must have begun with kind of rocks they could obtain. ‘Both genetic mutations, and these are still history and ecology are important, as being unravelled. is the case with most evolutionary problems,’ he says. These genetic studies combine with analysis of other traces from the past Then comes a more speculative part of to build up a picture of more recent the story – determining what the use of developments in human culture – such these techniques suggests about the as tool-making. different tool-users’ thought processes and systems of planning, co-operation Detailed examination of stone tools and communication. from many ancient sites can be used to map a new kind of gradual change Frontal view of a cast of a skull belonging to Homo sapiens Le Vieillard, adult male about 45 years – cultural evolution. Robert Foley, of age. Director of the Leverhulme Centre for © Natural History Museum, London. 36 37  Left: Flint hand axe from the late Palaeolithic period, England. The past in the present © Natural History Museum, London. The emergence of modern humans is Fossil bones remain an important a long story that begins in our proto- element. They have been used to human past. It can be told only from reconstruct a human lineage in which traces that survive in the present. the ancestors of modern humans Human and chimp DNA, for example, diverged from our extinct relatives – show two possible outcomes from the the australopithecines – about two last common ancestor of the two million years ago. species, which lived between four and six million years ago. But this does not Over roughly the same period, many Below: Left to right: Australopithecus africanus; reveal when gene changes between stone tools have survived. These can Homo rudolfensis; Homo erectus; Homo the two present-day species happened, be studied as a record of cultural, heidelbergensis; Homo neanderthalensis; or in what order. As in the comparative rather than biological evolution. and Homo sapiens. Arranged in chronological anatomy of bones, which was Over time, these tools became more order these specimens (casts) illustrate becoming a more precise study in varied, more complex, and needed human evolution. Darwin’s day, there is abundant scope more complicated preparation. © Natural History Museum, London. for argument. Comparing tools from different sites, and tools that can be dated to different The same is true of samples of times, reveals how early humans’ Neanderthal DNA, which allow cultural capacities developed. comparison with a much closer relative of modern Homo sapiens – and are The challenge then is to bring fossil taken from bones that are 45,000 and DNA evidence together to give years old. However, to go further back, a more complete account of how the scientists need data from material that diverse strands of evolution worked endures longer than DNA. together – as brain, hands and tools helped primate bands turn into human societies. Background: A chimpanzee using a grass stem as a tool to fish for termites. © Clive Bromhall/www.osfimages.com. 38 39 10 HOW DID MUSIC EVOLVE? Wherever people are found, there is music, but Speech and music both involve sound. Steven Mithen of the University Which came first – music or language of Reading, England, has recently how did music-making evolve? Darwin raised the – remains unclear. Scientists can study advanced a different view. Drawing on question, but found no answer. The difficulty was changes in the vocal tract as early archaeology, fossil evidence, and humans developed, but the sounds studies of brains, genes, language and in determining what advantage is offered to the they made leave no trace. Studies of music in many cultures, he suggests music-maker by the making of music. modern brains show that some regions that music and language both are involved in both understanding emerged from a common precursor – language and interpreting music. a quasi-musical use of sound – which Yet there are people who are both our ancestors used for communicating. tone deaf and non-stop talkers. These complex calls could have found uses as infant lullabies or as part of Some Darwinian theorists, such as the group celebration. He also suggests Harvard psychologist Steven Pinker, that the groups that developed this use have suggested that music is an of sound had more offspring and more accident, not an adaptation. It satisfies descendants, which is why music- our ears in the same way that a slice making survives today. However, this of cake appeals to our taste buds. route to reproductive success is more complex than simple mate choice. Others, following Darwin himself, think sexual selection is important. Geoffrey Miller of the University of New Mexico argues that music is driven by mate choice. Simply put, musical performance is rather like the courtship display seen in many other species. Bells on a classical Indian dancer’s ankles. © Francois Boutemy. 40 41  Humans and music In his book The Descent of Man, and Steven Mithen’s story of the evolution Selection in Relation to Sex (1871) of human music – described in his Darwin considered the elements that book The Singing Neanderthals: The set humans apart from other creatures Origins of Music, Language, Mind and – language, for example, and the ability Body – brings all these things together. to create culture. He was convinced He speculates that our primate that these qualities had evolved in the ancestors evolved complex vocal calls same way as any other characteristic. that were a little like singing. They Above left: Musician from Benin with flute and Music, however, was perplexing. would be accompanied with gestures, small percussion instrument. ‘As neither the enjoyment nor the which became more elaborate when © Peeter Viisimaa. capacity of producing musical notes hands were freed by walking upright. Above: Marine band playing bagpipes. are faculties of the least use to man... © Joseph Luoman. they must be ranked among the most The result, he suggests, was a mysterious with which he is endowed,’ communication system that preceded Left: Girls playing a Chinese drum. he wrote. language and music. It used emotion, © Jorge Delgado. conveyed by varying pitch, just as Below: Women playing the traditional Japanese Darwin argued that music arose parents now use wordless sounds instrument, the kato. through sexual selection – as did the to communicate with babies. © Radu Razvan. sounds made by other species he wrote about, such as frogs, toads, All of this helped bind groups together, tortoises, alligators, birds, mice and and perhaps cemented co-operation, gibbons. Humans, however, do more therefore increasing survival rates. than just sing (or hum, chant or From this early communication whistle). We also have a sense of emerged the universal use of music rhythm – expressed in drumming and dance in ritual and celebration, or dancing – that is not found in which still appear to reinforce group other creatures. ties in modern human societies. Background: Sheet music score. © Peter Zelei. 42 43 11 HOW DO GENOMES EVOLVE? Genetic change is the motor of evolution. A single change in a gene’s DNA sequence might be of no consequence or it might be damaging, leading to a defective protein molecule; occasionally, it might be advantageous. In the 21st century, the story is While work on this continues, other becoming more complex. Biologists studies of genomes have shed light on are now looking at entire genomes – larger mechanisms of evolution. ‘Junk’ the complete library of DNA in each DNA can contain non-functional genes cell of an organism. – a kind of genetic fossil – or it may contain duplicates of important genes. The human genome, for example, has If there is an extra copy of such a 3,400,000,000 DNA ‘letters’, known as gene, it does not matter if mutations bases and labelled chemically C, A, T, slowly build up. This means the or G. However, the 25,000 or so organism can experiment with varied human genes take up less than two per forms of the gene that may, in turn, find cent of this massive total. So, what is entirely new uses. Much more rarely, the rest of that DNA doing? copying mistakes can lead to duplication of an entire genome. This It might be ‘junk’ – a kind of harmless seems to have happened several times molecular parasite. If so, mutations in during the evolution of creatures with the vast majority of the genome would backbones, for example. Some go unnoticed, but we now know that researchers suggest – controversially large parts of these sequences are – that such full-scale duplications are conserved. Natural selection has vital for the development of more removed any random changes in the complex creatures. Mustard weed (Arabidopsis thaliana), the first plant to have its genome sequenced. DNA, so it must be used for something. Courtesy of the National Human Genome Research Institute. 44 45  Modelling the genome Now biologists are becoming familiar Professor Laurence Hurst of Bath with all the genes in a single organism University in the UK, with collaborators – its genome – they would like to know in Manchester, Heidelberg, and how big a genome has to be. What Budapest, approached the question does any organism need to stay alive? by developing a different technique for The simplest organisms ought to have modell