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Transcript
Evolution Lesson objectives By the end of this lesson you should know that • Variation is the result of sexual reproduction and mutations. • Discuss two agents responsible for increased mutation rates. Variation “Variation means that there are differences between the members of a species” • Only inherited (genetic) variations are considered here • Acquired variations are not passed onto the next generation • Genetic variation is caused by sexual reproduction and by mutations Mutations “A mutation is a change in the amount or structure of DNA” • Mutations happen naturally when DNA fails to replicate properly – this rate of mutation is normally very low • In addition, DNA has enzymes that repair the vast majority of mutated genes • Mutations occur at random locations on the chromosome • The change in DNA normally means the protein cannot be made • This can mean there will be serious problems if the protein is important for the cell • Mutations in somatic cells may be sometimes serious – cancer • Mutations in gametes are very serious because the mutation may be passed onto the cells of the offspring Causes of mutations • Agents called mutagens can increase the natural rate of mutations • Mutagens that cause cancer are called carcinogens • Mutagens include: 1. Ionising radiation such as X-rays, gamma rays and ultra-violet radiation 2. Chemicals such as cigarette smoke, caffeine and formaldehyde Types of mutations – 2 types Gene mutations • Gene mutations affect only small sections of DNA (i.e. affect only 1 gene) • These mutations cannot be seen but their effects can • Examples: albinism, cystic fibrosis, sickle cell anaemia Types of mutations – 2 types Chromosome mutations • Chromosome mutations affect large areas of a chromosome or can involve an entire chromosome and sets of chromosomes • Examples Down’s Syndrome (results normally from the egg containing 24 chromosomes combining with a normal gamete of 23 chromosomes) What do you know? Do you know that . . . • Variation is the result of sexual reproduction and mutations. • Discuss two agents responsible for increased mutation rates. Lesson objectives By the end of this lesson you should know the: • Definition of "evolution". • Theory of Natural Selection. Evidence from any one source. Evolution • • • • • “Evolution is the way in which living things change genetically to produce new species over long periods of time” Theory proposed by Charles Darwin in 1858 Got many of his ideas when he worked on board the HMS Beagle The ship sailed around the Galapagos islands in the 1830’s Alfred Russel Wallace has come up with the same ideas around the same time Wallace stimulated Darwin to publish their joint theory Charles Darwin • English naturalist • Born 1809 • While studying theology he became interested in natural history • 1831 - invited to join an expedition to map coastline of South America HMS Beagle The Voyage The Voyage In Brazil he saw his first tropical forest The Voyage (Argentina) • In Argentina he found his first fossils – sloths, mastodons, and horses The Voyage (Chile) • In Chile, Darwin witnessed an earthquake and observed both its effects in raising the level of the land and its connection with volcanic eruption. Repeatedly when ashore he went on long, arduous, and dangerous expeditions on horseback, collecting and shooting, which showed that his addiction to sport had not been useless. The Galapagos Islands The Galapagos Islands are located 650 miles west of Ecuador in the Pacific Ocean. Species on the islands • Dozens of unique species of both plants and animals found nowhere else in the world • Giant tortoises • A comorant that has lost its ability to fly • The only lizard that feeds in the sea • The only equatorial penguin in the world Galapagos reptiles Giant Tortoises Harriet – she didn’t look a day over 154 • Harriet was one of three tortoises Darwin brought back from the Galapagos Islands to England • Subsequently, he gave Harriet to a friend heading for Australia • Harriet was mistakenly considered a male for over 100 years • She died in June, 2006 at an Australian Zoo where she’s been a key attraction for years Galapagos birds Galapagos birds A unique form of giant cactus Darwin’s visit to the Galapagos • Darwin’s visit to the Galapagos for 5 weeks in 1835 provided the starting point for his theory of natural selection • He did not understand a great deal of what he was seeing when he was there • It wasn’t until he got back to England and had ornithologist John Gould and other experts look at the finches that he realized he had discovered something big The different types of finch • The diversity of beak structure and feeding habits within the group of finches is remarkable • The different species are adapted to feed in a variety of ways • Some eat seeds • Some eat insects • Some remove ticks from tortoises • Some eat leaves • Some eat flowers • Some drink blood from seabirds • Some use twigs to extract insect larvae Back Home • At first his interests were geological e.g. he discovered in the Andes – at an altitude of 7000 feet – a fossil forest overlain by thousands of feet of sedimentary deposits laid down by the sea, thus proving the occurrence of earlier earth movements of the order of 10,000 feet vertical height • In 1856 Darwin started to put on paper his discoveries about evolution and natural selection Back Home • In 1858 out of the blue, he received from Alfred Wallace, a naturalist then in the Malay Archipelago, a succinct but complete statement of his own conclusions on evolution and natural selection • A joint paper by both was read to the Linnean Society of London in 1858 • Darwin then made an abstract of the work on which he had been engaged for 20 years • This abstract was called the Origin of Species which was published on November 24, 1859, and sold out immediately “Origin of Species” • In the eyes of posterity, his publications on geology were so eclipsed by the bombshell on evolution that they have been neglected • With his book Darwin brought down on himself enemies of two kinds. Scientists (Adam Sedgwick and Richard Owen) and upholders of orthodox religious beliefs e.g. Samuel Wilberforce, bishop of Oxford What was in the book? • In it, Darwin makes one long argument with copious examples as support, for his theory that organisms gradually evolve not individually but in groups through the process of natural selection, a mechanism the book effectively introduced to the public. Summary – statements 1 and 2 • S1 Organisms produce far more offspring than ever give rise to adult individuals • S2 The numbers of individuals of a species remain more or less the same (in a particular ecosystem) Deduction 1 • Therefore there must be a high death rate, resulting from the constant struggle taking place between all organisms for food, in avoiding predators and disease, and in coping with climatic conditions Statement 3 • S3 The individuals in a species are not all identical, but show variations in their characteristics that have arisen, by chance, through sexual reproduction and mutations Deduction 2 • In the competition for survival, variations allow some individuals to adapt, survive and reproduce better than others, so passing on these ‘successful’ traits to their offspring. Over many generations, these small changes accumulate until two groupings within the population can no longer interbreed and a new species is formed Evolution “Evolution is the changing of one species into another that takes place through natural selection” Evidence for evolution • • • • Palaeontology: The study of fossils Comparative Embryology Comparative Anatomy Comparative Biochemistry Palaeontology • Fossil Record ( Palaeontology) • Fossil = Remains of an organism or evidence that it once existed Fossils • Actual remains e.g. Bones and Teeth • Rock Fossils e.g. Casts or impressions of organisms and petrifaction of organisms • Ice Fossils e.g. Woolly Mammoths in Siberia • Amber Fossils e.g. flies trapped in resin which becomes amber. Palaeontology • Sedimentary rocks are laid down in layers making it possible to date the fossils in each layer. The organisms in the lower layers being older than those in the top layers. The changes which occurred over time can clearly be seen in clear, simple and sequential fossil records Comparative embryology • Embryos of different species tend to pass through the same stages of development e.g. Human embryos have gill slits at an early stage • The similarities in the these stages of development can reflect the evolutionary relationships between organisms • The genes for basic embryo development e.g. Hox genes are shared by many complex animals Comparative anatomy Biochemistry • If you compare the chemicals e.g. DNA, Haemoglobin, ATP found in different animals and plants, the degree of similarity between these organisms can be measured • There is a 1% difference between our DNA and that of Chimpanzees Famous debate at Oxford 1860 • Thomas Huxley “Darwin’s bulldog” vs Archbishop Samuel Wilberforce “Soapy Sam” • Wilberforce was coached against Huxley by Richard Owen , a biologist • Wilberforce ridiculed evolution and asked Huxley whether he was descended from an ape on his grandmother’s side or his grandfather’s • One account has it that Huxley concluded his brilliant defence of Darwin’s theory, by saying “ I would rather be the offspring of two apes than be a man and afraid to face the truth” Evolution • Note: there is no direction or plan to Evolution; it is merely the rule book for the game of life. • As Darwin concluded his book “The Origin of Species by Natural Selection “ • “There is a grandeur in this view of life, with its several powers, having been originally breathed by the Creator in a few forms or into one ; and that, 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 wondrous have been and are been evolved” Other examples of Natural Selection in action include: • Evolution of pesticide resistance in beetles, incidence of sickle cell anaemia in areas which historically had malaria and the evolution of antibiotic resistance in bacteria. How Evolution Works - Natural Selection Both – unpolluted area Both – polluted area Biston Betularia,had the •• The environment Peppered Moth changed and now for themoth black • selected The peppered form of the moth, so by comes as two forms, a 1898 in one the polluted typical which is areas of Englandcoloured like peppered to Manchester black camouflage the itself on the form made up over 95% lichen covered barks of of the and moths population trees a mutant black and peppered form formthe which was first less thanin5% noticed 1848 in Manchester • This process is known as Selection • Natural Pollution from the Industrial Revolution in England killed the lichens on the trees and covered their barks with soot making them black Religious problems • The issues for religious believers were two fold • If evolution was true, the account of the Creation in the Book of Genesis was false or, at least not literally true • If evolution worked automatically by natural selection, there was no room for divine guidance and design in the production of living plants and animals, including man on earth. • Darwin’s findings became well known but eventually gave Fitzroy great distress because he was a creationist Darwin’s Theory of Evolution o Many are born o Not all survive o Individuals vary o Variations are inherited o ‘Useful’ variations increase What do you know? Can you . . . • Define "evolution". • Discuss the theory of Natural Selection and give evidence from any one source.