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Darwin’s Theory of Evolution Chapter 15 1 15-1 The Puzzle of Life’s Diversity Darwin’s observations – Patterns of Diversity Organism well suited to live in particular habitat Similar habitats in different parts of the world contained different animals – Fossils Some similar to living organism Some completely different than living organisms 2 15-2 Ideas That shaped Darwin’s Thinking An Ancient, Changing Earth – James Hutton 1795 – Earth is millions of years old – Charles Lyell 1831 – geological process The Earth is approximately 4.5 billion years old Scientist use radioactive elements to date earth p. 420 Rock Layers help to set up geological time scale p.419 3 Early Explanation of Evolutionary Change Jean Baptiste de Lamarck (1744 – 1829) – Realized organisms somehow adapted to their environment – Thought that organisms changed in response to their environment Due to an inborn urge to better themselves and become more fit for their environment Change occurred by using body part in a new way A body part would become smaller and might disappear if not used 4 Lamarck continued Lamarck also believed that acquired characteristics were inherited by offspring. We now know Lamarck was incorrect. 5 Ideas That Shaped Darwin’s Theory Voyage on the HMS Beagle Diversity of Life Geology Age of the Earth The Earth changed over time 6 Ideas That Shaped Darwin’s Theory (continued) Farmers – Artificial Selection – Farmers altered and improved their live stock and crops – Farmers could not cause variations but could utilize them once observed Thomas Malthus – Population Control – The human birth rate is higher than death rate – Eventually we will run out of living space and food – However, famine, disease and war would limit endless population growth 7 15-3 Darwin Presents His Case Evolution by Natural Selection Struggle for Existence– Competition for life’s basic needs Survival of the fittest – Darwin called the ability to survive Fitness – Darwin also stated that fitness was result of adaptations- inherited characteristics that increase an organisms chance of survival 8 Survival of the fittest cont. Individuals whose characteristics are well-suited for their environment will survive. Those individuals whose characteristics are not well suited for their environment either die or produce fewer offspring – survival of the fittest. 9 Continued Descent with modification– Over long periods of time natural selection produced varying organisms Niches, habitats, structure – Organisms look different from ancestors This is known as descent with modification Common Descent – Descent with modification also implies that all living organisms are related 10 Natural Selection in Action: Peppered Moths 11 Evidence of Evolution The fossil Record Fossils are the remains of living organisms Found in sedimentary rock The fossil record shows life has changed over time 12 Evidence Continued Beaver Geographic Distribution of Animals Beaver NORTH AMERICA Muskrat Muskrat Beaver and Muskrat Coypu Capybara Capybara SOUTH AMERICA Coypu and Capybara Similar habitats in different parts of the world contained different animals Different animals had similar adaptations Coypu 13 Cont. Similarities in Embryology Similarities in the structure and development of embryos gives evidence of a common ancestor NOVA Online/Odyssey of Life/Morphing Embryos 14 Homologous structures are evidence of a common ancestor 15 Vestigial Structures are also evidence of a common ancestor 16 Similarities in biochemistry of organisms is evidence for a common ancestor. DNA 17 Summary of Darwin’s Theory Individual organisms differ and some variation is heritable Organisms produce more offspring than survive Organisms compete for resources Natural selection Descent w/ Modification/Common Descent 18 Evolution of Populations Chapter 16 19 16-1 Genes and Variation Variations and Gene Pools Evolution is the change in the relative frequency of alleles in a gene pool of a population Population – collection of organisms of the same species Gene Pool – common group of genes in population Relative Frequency – the number of times an allele appears in a gene pool compared to the number of times other alleles for the same gene appear 20 Sources of Genetic Variation Mutation- change in genetic information Error during replication Environmental factor – radiation, chemicals Gene Shuffling – independent assortment, crossing over, sexual reproduction 21 Single – Gene and Polygenic Traits The number of phenotypes produced for a given trait depend on how many genes control the trait. 22 16-2 Evolution as Genetic Change Natural Selection on single- gene traits can lead to changes in allele frequencies and thus evolution. Pg. 397 fig 16-5 23 Natural Selection of Polygenic Traits Natural selection can affect distribution of phenotypes in three ways Directional selection Stabilizing selection Disruptive selection 24 Section 16-2 Figure 16–6 Graph of Directional Selection Key Directional Selection Food becomes scarce. Individuals at one end of the graph have higher fitness than individuals in the middle or other end of the graph. Low mortality, high fitness High mortality, low fitness 25 Figure 16–7 Graph of Stabilizing Selection Section 16-2 Key Low mortality, high fitness High mortality, low fitness Percentage of Population Individuals in the center of the curve have a higher fitness than individuals at the ends of the curve. Stabilizing Selection Selection against both extremes keep curve narrow and in same place. Birth Weight 26 Figure 16–8 Graph of Disruptive Selection Section 16-2 Disruptive Selection Low mortality, high fitness High mortality, low fitness Population splits into two subgroups specializing in different seeds. Number of Birds in Population Key Number of Birds in Population Largest and smallest seeds become more common. Beak Size Beak Size Individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. 27 Genetic Drift Genetic Drift – Random change in the frequency of a alleles Occurs most efficiently in a small population Can happen by chance Natural disasters, Chance, Migration (Founder Effect) 28 Evolution vs. Genetic Equilibrium Hardy-Weinberg Principle Allele frequency will remain constant unless one or more factors causes those frequencies to change Five conditions required to maintain equilibrium Must be random mating Large population No movement into or out of population No mutation No Natural selection 29 16-3 The Process of Speciation Species A group of similar looking organisms that breed with one another and produce fertile offspring in a natural environment Speciation – is the process of new species evolving from old species 30 Isolating Mechanisms Reproductive Isolation when members of two populations cannot interbreed, gene pools become separated React to natural selection and genetic drift independently Behavior Isolation Geographic isolation Temporal Isolation 31 Behavior Isolation Organisms may be capable of interbreeding but have different courtship rituals or other reproductive strategies that involve behavior. Great Horned Owl Barred Owl 32 Geographic Isolation When two populations are separated by geographic boundaries such a s river, mountains or body of water 33 ERROR: undefined OFFENDING COMMAND: ‘~ STACK: