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Evolution Chapter 6
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Pre-Darwinian Theories http://anthro.palomar.edu/evolve/evolve_1.htm
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Darwin’s Voyage Where did he go and why? 5 year trip around the world on the HMS Beagle in 1831 To learn about living things as the ship’s naturalist Saw many living things different from life in England
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H.M.S. Beagle
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A Brief Biography of Charles Darwin
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Darwin's Observations Amazed by the diversity of life Large sloth bones in Argentina Many diverse species in the Galapagos islands Species: a group of similar organisms that can mate with each other and produce fertile offspring
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A species is often defined as a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions. For example, these happy face spiders look different, but since they can interbreed, they are considered the same species: Theridion grallator. Variations in the Species!
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Similarities and Differences How did Darwin think plants and animals had originally come to the Galapagos Islands? He inferred: Blown out to sea during a storm Adrift on a fallen log Reached the islands, reproduced Offspring eventually became different from mainland species Species differed island to island
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The Galapagos Islands
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Adaptations Adaptation: a trait that helps an organism survive and reproduce Tortoises’ shells Finch beaks Traits are controlled by genes!
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Adaptations
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Darwin’s "Dangerous" Idea Perhaps the species became better adapted to the new conditions He did not know how it happened Thought it might be similar to selective breeding evolution: gradual change in a species over time
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Natural Selection Explanation proposed by Darwin and Alfred Russel Wallace about how evolution occurs Process by which individuals better adapted to environment are more likely to survive & reproduce Factors: overproduction – competition – variations - selection
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Overproduction Most species produce more offspring that can survive Not enough resources available for all: food; water; space Ex: salmon lay hundreds of eggs but few survive to adulthood Darwin wondered why?????
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Variations Difference between individuals of same species Genetic! EX: some salmon have a "notch" in their tails Could help them survive
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Adaptation/Competition Indirectly for available resources Not usually physical Ex: fish with notch swim faster & escape predators Some don’t escape predators
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Selection Some variations = better adapted More likely to reproduce Offspring may inherit helpful alleles More individuals have trait after many generations ENVIRONMENT does the “selecting” Natural selection can lead to evolution over a long period of time Ex: more salmon with notched tails
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Natural Selection
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The Role of Genes in Evolution Darwin knew nothing of genes or mutations He could not explain how traits were passed on Now: Only inherited traits are acted upon by natural selection
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Evolution in Action 1977 study on Daphne Major Little rain led to fewer plants Fewer plants = fewer seeds Finches ate large, tough seed pods Many small-beaked finches did not survive drought Next year = more finches with larger, stronger beaks
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Daphne Major & Minor
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Evolution in Action Peppered moths of England
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How Do New Species Form? Geographic isolation A group of individuals remains isolated long enough to evolve different traits Ex: Kaibab & Abert squirrels
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Kaibab Squirrel Abert Squirrel The Kaibab squirrel is isolated in the Kaibab Plateau. South of the canyon and elsewhere, the similar Albert squirrels may be found.
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How Do New Species Form? isolation = when some members of a species are cut off from the others a new species can form when a group of individuals remains separated from the rest of his species long enough to evolve different traits
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Continental Drift As continents separated species became isolated Began to evolve independently Australia and the marsupials and monotremes
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Pangea Pangaea & Continental Drift
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