science education teaching booklet

Name: Galapagos Islands-Natural Selection The Galapagos Islands are a group of very rugged and isolated volcanic islands found about 1000 km west of the South American mainland. Today they are a tourist destination for people who are fascinated by the variety of unusual wildlife found there. They have become famous because of the nineteenth century naturalist Charles Darwin. After a visit in 1835, he felt challenged to explain why the wildlife was so different from that found anywhere else in the world. Darwin was travelling on HMS Beagle, as an unpaid ship's naturalist. This sailing ship had left England at the end of 1831 to survey the South American coastline and nearby islands. It was Darwin's job to study the geology, plants and animals at each destination on the 5-year voyage. He spent 5 weeks on the Galapagos Islands and recorded his careful observations in a journal. Unusual animals The animals on the islands were very unusual. Giant tortoises had inspired their name (galapagos is Spanish for turtle). For centuries, sailors had called at the islands to capture tortoises for food. Each island had a different variety of tortoise. Darwin was amazed by their size and strength. He could not lift them but he did take a ride on one. The tortoise kept walking and did not seem affected by the extra weight. He wrote in his journal: I never dreamed that islands, about fifty or sixty miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a near equal height, would have been differently tenanted. Darwin observed ferocious-looking giant lizards called land iguanas eating prickly pear cactus. Darwin described them as 'essentially mild and torpid monsters'. There were also seagoing iguanas. These marine iguanas had different colours and markings, depending on which island they were from. They had blunter noses than In 1858, Wallace sent Darwin a copy of an essay he had written. The essay talked about a struggle for existence in natural populations and the survival of those organisms that were better adapted to the environment. Darwin now realised that he had waited too long to publish his ideas. He hurried to complete his book, which was published in 1859. It contained 500 pages of detailed evidence and argument for his theory. 2 Great evolution debate Only 1250 copies of Darwin's book were printed initially, and every copy was sold on the first day of publication. A storm of controversy followed. In the seventeenth century, Galileo had been forced to renounce his ideas that the Earth moved around the Sun. Not since that time had there been such a public controversy about a scientific theory. The scientific community, the clergy and the general public condemned Darwin. One clergyman described him as 'the most dangerous man in England'. A public debate on Darwin's theory was held in June 1860 at the annual meeting of the British Association for the Advancement of Science. (This was a forum where scientists and people interested in science could discuss scientific issues.) Darwin was a quiet, unassuming man who was not confident as a public speaker. He was in poor health and staying at his country home at the time. Thomas Huxley, a One way that Darwin's theory was misrepresented was to say that he claimed famous biologist people were descended from apes as in this and brilliant 1871 cartoon. The ape is pointing to Darwin speaker, and crying: 'This man wants to claim my accepted the role pedigree. He says he is one of my descendants'. The other man, the founder of of publicly the Society for the Prevention of Cruelty to defending Animals, replies: 'Now, Mr Darwin, how could Darwin's ideas. you insult him so?' In fact, at the end of On One of the the Origin of Species Darwin speculated that 'Light will be thrown on the origin of man and opponents of his history' but he made no further mention Darwin's theory of human origins at that time. In a later was Richard book, he suggested that apes and man had a Owen, a common ancestor in the distant past. Darwin never claimed that man had descended from zoologist who apes. was the world's leading authority on dinosaurs and extinct life. However, it was the Bishop of Oxford, Samuel Wilberforce, a brilliant orator, who presented the case against Darwin's theory that evening. More than 700 people crowded into the Oxford University library to hear the debate. Wilberforce denounced Darwin and ridiculed his ideas in front of a cheering audience. He then asked Huxley was it through his grandmother or grandfather that he claimed to be descended from an ape. Huxley presented his arguments in support of Darwin's theory. When he said that he would prefer to have an ape for an ancestor rather than be related to someone who would 'introduce ridicule into a grave scientific debate' (as Wilberforce had just done), there was laughter and uproar in the audience. Unexpectedly, a second supporter for Darwin came forward. Joseph Hooker was England's leading botanist. He took the stage and spent over 2 hours explaining Darwin's ideas calmly but with conviction. Darwin's supporters felt that this was a turning point, but Wilberforce felt he had won the day. In the following years, with gifted advocates like Huxley and Hooker, Darwin's ideas began to be accepted by the scientific community but debate about his theory of evolution continued into the twentieth century. Darwin himself lived a quiet life in the country, suffering from a mystery illness which he had probably contracted in South America on his Beagle voyage—but his theory required such a 'mind-shift' in thinking that it 'broke on the world like a thunderbolt' (Isaac Asimov). 3 Questions 1 What unusual animal life did Darwin find on the Galapagos Islands? ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ 2 What features make marine iguanas different? ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ Darwin had developed his theory of evolution by natural selection by 1838, yet he did not publish his ideas until 1859. Why did he take so long? ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ The ideas of two scholars helped Darwin to develop his theory about natural selection. Who were they and what were their theories? ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ Complete the following Word Bank: plant evolution debated book gradual Beagle University naturalist studied voyage 1859 Man 4 3 Charles Robert Darwin (February 12, 1809-April 19, 1882) was an English naturalist who revolutionized scientific thought with his theory of ____________________ and natural selection. After studying at Cambridge ____________________, Darwin served as ____________________ on the ship HMS ____________________ (captained by Robert Fitzroy) during its five-year ____________________ around the world traveling west ( December 27, 1831-October 2, 1836). On this trip, Darwin ____________________ a tremendous variety of ____________________ and animal life. Darwin's ____________________ called "Origin of the Species" was published on November 24, ____________________ (and sold out in one day). This world-shaking book outlined the ____________________ change in a species from generation to generation through natural selection. 4 Alfred Lord Wallace independently proposed the theory of evolution at the same time as Darwin. In 1871, Darwin published "The Descent of ____________________," which focused on the origins of people. The theory of evolution has been ____________________ since it was proposed, but most scientists accept evolution and natural selection as the method of species formation and the foundation of biology. Variation is the natural difference between living things. Animals and plants that are produced by sexual reproduction always vary from their relatives. This is because each one has its own unique collection of genes. Variation is important because it enables a species to change slowly through the process of evolution. A population of living things has three sources of variation: • Immigration of individuals with new genes into a population. • Recombination of genes during meiosis (Cell division which results in daughter cells having half the number of chromosomes as the parent cell) • Mutation. Varieties of finches While visiting the Galapagos Islands in 1835, Charles Darwin was puzzled to find different species of finch on each island. He struggled to explain why these differences might exist. Of all the animals he observed, it was the finches that had the deepest influence on his thinking. He observed finches with beaks like small parrots. They had a mixed diet of insects, flowers and fruit. The warbler finch had a thin pointed beak and ate only insects. The woodpecker finch used twigs or cactus spines to pries insects out of bark. Other finches ate only seeds. All these finches were different from the finches he had observed on the South American mainland. Variation of Species 1 How do you think the different beak type enables each finch to be best suited to its food source? ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ ______________________________________________________________________________________________________ 2 What time frame do you think would have been involved in the evolution of the different beak types? ______________________________________________________________________________________________________ 3 Look at the beak of the ancestral finch. To what type of food do you think it is suited? ______________________________________________________________________________________________________ 5 Biodiversity and survival The work of Charles Darwin had a huge impact on the way people thought. In his own lifetime he was regarded as a great scientist and thinker by some people, but as a dangerous and downright foolish man by most. Darwin’s work shocked the many people who believed that all living things were created in their present form by God. To people who believed that the different human races were completely unrelated it was even more shocking to read that we are all descended from an ape-like ancestor. Today his theories are generally accepted and need not conflict with our religious beliefs. They give us a deeper understanding of our place in the living world, and encourage us to respect all living creatures. Read the passage below about Darwin’s theory of evolution and then answer the following questions. In 1832 a young Englishman, Charles Darwin, twenty-four years old and naturalist on HMS Beagle, a brig sent by the Admiralty in London on a surveying voyage round the world, came to a forest outside Rio de Janeiro. In one day, in one small area, he collected sixty-eight different species of beetle. That there should be such a variety of species of one kind of creature astounded him. He had not been searching specially for them so that, as he wrote in his journal, ‘It is sufficient to disturb the composure of an entomologist’s mind to look forward to the future dimensions of a complete catalogue.’ The conventional view of his time was that all species were immutable and that each had been individually and separately created by God. Darwin was far from being an atheist—he had, after all, taken a degree in divinity in Cambridge—but he was deeply puzzled by this enormous multiplicity of forms. The suspicion grew in Darwin’s mind that species were not fixed for ever. Perhaps one could change into another. Maybe, thousands of years ago, birds and reptiles from continental South America had reached the Galapagos, ferried on the rafts of vegetation that float down the rivers and out to sea. Once there they had changed, as generation succeeded generation, to suit their new homes until they became their present species. The differences between them and their mainland cousins were only small, but if such changes had taken place, was it not possible that over many millions of years, the cumulative effects on a dynasty of animals could be so great that they could bring about major transformations? Maybe fish had developed muscular fins and crawled on to land to become amphibians; maybe amphibians in their turn had developed water-tight skins and become reptiles; maybe, even, some ape-like creatures had stood upright and become the ancestors of man? In truth the idea was not a wholly new one. Many others before Darwin had suggested that all life on Earth was interrelated. Darwin’s revolutionary insight was to perceive the mechanism that brought these changes about. By doing so he replaced a philosophical speculation with a detailed description of a process, supported by an abundance of evidence, that could be tested and verified; and the reality of evolution could no longer be denied. Put briefly, his argument was this. All individuals of the same species are not identical. In one clutch of eggs from, for example, a giant tortoise, there will be some hatchlings which, because of their genetic constitution, will develop longer necks than others. In times of drought they will be able to reach leaves and to survive. Their brothers and sisters, with shorter necks, will starve and die. So those best fitted to their surroundings will be selected and be able to transmit their characteristics to their offspring. After a great number of generations, tortoises on the arid islands will have longer necks than those on the watered islands. And so one species will have given rise to another. This concept did not become clear in Darwin’s mind until long after he had left the Galapagos. For twenty-five years he painstakingly amassed evidence to support it. Not until 1859, when he was forty-eight years old, did he publish it, and even then he was driven to do so only because another younger naturalist Alfred Wallace, working in South-east Asia, had formulated the same idea. He called the book, in which he set out this theory in detail, The Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. Since that time, the theory of natural selection has been debated and tested, refined, qualified and elaborated. Later discoveries about genetics, molecular biology, population dynamics and behaviour have given it a new dimension. It remains the key to our understanding of the natural world and it enables us to recognise that life has a long and continuous history during which organisms, both plant and animal, have changed, generation by generation, as they colonised all parts of the world. From Life on Earth, David Attenborough (BBC/Collins 1979) 1 Describe Darwin’s theory of natural selection. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 6 2 Describe an example of natural selection from the passage. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 3 What examples of variation and adaptation are used in the passage? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 4 Explain some of the ways in which the theory of evolution affected people’s lives and thinking. ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ 5 Do you believe Darwin’s ideas? What weaknesses exist in his theory? What further evidence would you like to find? ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ What about other theories Frenchman, Jean Baptiste Lamarck, proposed a theory of evolution in 1809 that stated that animals have some organs and structures that they do not use. The ones that they do not use would eventually deteriorate and the ones that were used would be strengthened and passed on to offspring. He also stated that animals would be able to acquire certain characteristics if they needed them for their survival. Lamarck's theory for evolution depended on the inheritance of acquired characteristics. Notable scientists of the time criticised the theory and denounced the author because he was not accepting the biblical explanation for creation. This was at a time when Charles Darwin was preparing his own explanation for how evolution had occurred. The public arguments made him even more cautious and reluctant to publish his theory about natural selection. Theory vs. Theory The Giraffe Problem 7 Lamarck Lamarck would argue that giraffes have long necks because each generation has stretched its neck a little as it reached up to get leaves from tall trees. Darwin Darwin would say that at times of food shortage, giraffes that happened to have a slightly longer neck could have reached up to higher trees to get food; therefore they could survive and multiply to pass on their slightly longer neck to the next generation. Explain the difference between the use of these words: Need ________________________________________________________________________ ________________________________________________________________________ Acquire ________________________________________________________________________ ________________________________________________________________________ Variation ________________________________________________________________________ ________________________________________________________________________ Exists ________________________________________________________________________ ________________________________________________________________________ Evidence of evolution 8 Fossil Evidence One of the best studied cases in the fossil record concerns the evolution of horses. Modern-day members of the Equidae include horses, zebras, donkeys and asses, all of which are large, longlegged, fast-running animals adapted to living on open grasslands. These species, all classified in the genus Equus, are the last living descendants of a long lineage that has produced 34 genera since its origin in the Eocene Period, approximately 55 million years ago. Examination of these fossils has provided a particularly well-documented case of how evolution has proceeded by adaptation to changing environments. There is evidence from fossils that mammals and birds evolved from reptiles, which reptiles evolved from amphibia, and that amphibia evolved from fish. Embryology, or the study of embryos, provides more evidence that this happened. Embryos of mammals, birds, reptiles, and amphibia are so similar to fish embryos that it is difficult to tell them apart. All of these, including human embryos, have gill slits, a fish-like heart (with only one atrium and ventricle), fish-like kidneys, and a muscular tail. Human embryos later develop an amphibian heart (with two atria and one ventricle). Then their gill slits disappear and they develop reptilian kidneys. Finally they develop a four-chambered heart, lose their tail, and develop mammalian kidneys. In other words, during embryonic development humans go through some of the stages by which they evolved from fish into amphibia, reptiles, and finally mammals. Animals such as moles, whales, horses, and birds are entirely different in shape, and live in entirely different ways, but the structure (anatomy) of their bodies has the same basic plan. Their circulatory, nervous, and excretory systems are similar, and their skeletons have roughly the same number and arrangement of bones. Key: Bird a. humerus b. radius c. ulna d. carpals Human Fish Bird e. metacarpals Humanand phalanges (fingers) Whale 9 The most satisfactory explanation of these similarities is that all these animals evolved from the same ancestor, whose basic anatomy they now share. In the course of evolution the anatomy of the forelimbs which these animals inherited from their ancestor has become adapted in many different ways: enabling moles to dig, birds to fly, whales to swim, horses to run, etc. The human hand also follows the ancestral plan, but is capable to performing an enormous range of intricate tasks. The Role of DNA At the time Darwin published On the Origin of Species in 1859, he and other scientists had no real understanding about genetics. However, Darwin did realise that natural selection would not occur unless there was variation in a population. Today, modern science can give explanations for how this variation in a population can occur. Variation can be caused by your genes, by the environment in which you live or by both of these factors. Your diet is part of your environment and it will affect your height, your weight and other features. Your genes can also affect these features. There are three main sources of genetic variation within any organism: meiosis, sexual reproduction and mutation. Meiosis In both ovaries and testes, gametes are produced by a form of genetic variation known as meiosis. Meiosis involves the separation of the homologous pairs of chromosomes in diploid body cells to form haploid gametes. As humans, we received 23 chromosomes from our mother and 23 chromosomes from our father. There is little chance that when our own eggs and sperm cells are produced the pairs of chromosomes will separate out exactly into the set from our mother and the set from our father. We are more likely to produce gametes that have a mixture of chromosomes Meiosis Cell division that results in daughter cells having half the number of chromosomes as the parent cell; gamete formation. Gametes: Sex cells; male gametes are called sperm and female gametes are called ova or eggs; contain half the number of chromosomes compared to normal body (somatic) cells. 10 from each of our parents. This means that the gametes we are producing by meiosis contain a blend of genes. The chance of any two gametes possessing an identical set of genes is less than 1 in 8 million! Sexual reproduction The random fusion of two gametes, one from each parent, in sexual reproduction leads to even greater variation. Mutation Mutation A model for variation within a species. Meiosis and sexual reproduction mix up existing genes and alleles. Mutation adds new ones. There are two types of mutation: genetic mutation and chromosomal mutation. Genetic mutations arise out of an alteration to the base sequences of DNA, which causes the gene to produce different proteins from normal and hence different characteristics. This type of mutation may have little effect on the organism, produce an advantageous characteristic, or have an adverse effect on the organism. Overall, however, it is responsible for a great deal of inherited variation in a population. Chromosomal mutations can lead to an abnormal number of chromosomes in a gamete or a change in the structure of the chromosome. The effects of chromosomal mutations are almost always more severe because the change involves thousands of genes. 1 How do meiosis and sexual reproduction lead to variation in a species? ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 2 What is a mutation? How does it contribute to variation in a species? Variation ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ 3 The following are all examples of variations in humans: hair colour; eye colour; height; sex; how good you are at science; blood group; how fast you can swim. Which are caused by genes, which by environment and which by both? ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Extinction: Going, Going ... Gone! Tho last thylacine or Tasmanian tiger died in Hobart zoo in 1933. It was described as having the head and teeth of a wolf, the tail of a kangaroo, the stripes of a tiger and the pouch of a possum. It measured between 150 and 180 cm long. The thylacine was thought of as a vicious killer of sheep and a danger to humans. Between 1840 and 1914 it was actively hunted and hunters received a bounty for each animal shot. Over 2200 thylacines were known to have been shot. By 11 1910 the numbers of thylacines had dropped very low and many of the remaining animals succumbed to disease, possibly passed on by domestic dogs. By the late 1920s Thylacines had become extremely rare;. The last shooting of a thylacine occurred in 1930. Extinction has been the fate of many species of animals in Australia in the last 150 years. Not all of these species were hunted and shot like the thylacine. Most died o u t because t h ei r h abitat was destroyed by the activities of humans. Scientists believe that when most animals lose their habitat they usually stay in that area and slowly die out. Individuals that do move will have to compete with existing individuals in the new area and in most cases there is a loser. The extinction process Abundance: The species is successfully Something threatens the species, such as hunting, new predators or disease, or its habitat may be destroyed. The population becomes split up and numbers drop. The species is now vulnerable to other threats not normally a problem, such as drought, disease and predators. The numbers of individuals in the species may now be very low. Continued threats to the remaining individuals. Extinction 12 Find each of the following words. E R O A C N A M O G B N I P I A M L L L V M T U C E S H H T A I X R U E I V C O F D E T A T V L C C T O R S E I A V M N T E O I T I S A N V P H T H O S T Y S S U E O O T I M S D T N H R I D G E R T R T A T S G C U S S C I Y T Y I V O N I E E O U T M T I O A I L C O P S E S H R I V L I N A M G D S E M L S C D N A A Y E E O N E G A E E T O O A C G I M S G A H S I F S T C L V D O E T R S A L G D A A I O C N E A L N A T O I O M S I N O S C T I E M H H O X U R L R T I G T I E S C O M E A I M U U H S S L U A R O S A Y T M O S S E A G L S H T R M I R I E O E R L E A C I L L T I L V O A A I U Y E R I O L L L I N R N L T E Y A H S R O I P E A O S C C S T T S O P T N E E E T N P Y C T L O A A M M E I O U S C O L S A I I Y R I O N L B M U V L G O C C A O R T E E T O C R U I I O I D A E S T E A I O G F M L V I E N M A E S T I S S T E C N I I V G G T T A A C I V O T V T I T F A T G C R I D S O E T S E S V E C V N N Y E A E M D S I A N I N A O N E E V L O T S E A A T I E R G A E Y C M I U E I I I S D M A Y M I I L R I G E T E N A T S E T Q S C E I Y D O I C O I A T M T L I E N O A A O T X C S A M O R D E I N V V S E G A E M N E S V C O E E A I Q T E T N C C E L T T N V S T G A U O R S I S I E L S N S I T A A U I S R A I I B H A S T U L N N G L extinction cast sedimentary species characteristics variation mould mutation genetic acquired evolution biodiversity chromosomal Thylacines survival fossils meiosis gametes genes Galapagos 13