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EVOLUTION Chapter 15 • Evolution - change over time • Theory – a well-supported testable explanation of phenomena in the natural world Charles Darwin The variety of living things… BIOLOGICAL DIVERSITY Darwin found a huge variety of living things, each well adapted to their environment Voyage of the Beagle 1831 Patterns of Diversity • Visited Argentina and Australiasimilar grassland ecosystems –those grasslands were inhabited by very different animals. Patterns of Diversity • Darwin asked questions… –Why no rabbits in Australia, despite the presence of habitats that seemed perfect for them? – Why no kangaroos in England? Living Organisms and Fossils • Darwin collected the preserved remains of ancient organisms, fossils. • Some of the fossils resembled organisms that were still alive today. Living Organisms and Fossils Others looked completely unlike any creature he had ever seen. • As Darwin studied fossils, new questions arose. –Why had so many of these species disappeared? –How were they related to living species? The Galapagos Islands • The smallest, lowest islands were hot, dry, and nearly barren-Hood Island-sparse vegetation • The higher islands had greater rainfall and a different assortment of plants and animals-Isabela- Island had rich vegetation. The Galapagos Islands • The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. More Galapagos Animals The Journey Home • Darwin Observed that characteristics of many plants and animals vary greatly among the islands • Hypothesis: Separate species may have arose from an original ancestor Ideas that shaped Darwin’s Thinking • James Hutton: • 1795 Theory of Geological change –Forces change earth’s surface –Changes are slow –Earth much older than thousands of years Ideas that Shaped Darwin’s Thinking • Charles Lyell • Geographical features can be built up/torn down • Darwin thought if earth changed over time, what about life? Lamarck’s Theory of Evolution • Tendency toward Perfection (Giraffe necks) • Use and Disuse • Theory of Acquired Traits (characteristics) Population Growth • Thomas MalthusEnglish economist • If population grew… –Insufficient living space –Food runs out –Darwin applied theory to animals and plants Publication of On the Origin of Species • 1859 after 25 years of study, thought, struggle • It outlined his theories of natural selection and evolution over time His Studies of Variation • Darwin didn’t know about genes • He DID observe traits being passed to offspring • He knew about Artificial Selection – nature provides variation, humans select variations they find useful • Dogs, pigeons, crops, horses, cows Natural Selection • There is a struggle for existence…living things need food, living space • Some individuals are better adapted for their environment • Adaptation – any inherited characteristic that increases an organism’s chance of survival SURVIVAL OF THE FITTEST Can you think of any adaptations? • Check out these examples of adaptations Descent with Modification • Darwin proposed that living things changed over long periods of time because of natural selection • It implies that all living organisms are related • Living things evolved from a common ancestor • Common Descent • Tree of Life links all living things Evidence of Evolution • Fossil Record • Geographic Distribution of living things • Homologous structures • Vestigial organs • Similarities in embryology Geographic Distribution of Living Things • Darwin found different species of animals on different continents • He recalled similar environments and sometimes similarities in different animals • Homologous Structures have different mature forms but develop from same embryonic tissues • Vestigial organs are traces of homologous organs • Ex. Legs in skinks (p. 385) Similarities in Embryology Similar in early stages…common ancestry?