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Origin of Life Theories of Evolution Lamark’s Explanation a. believed that traits were “acquired” and not determined by genes b. traits were results from organisms experiences or behavior c. “necks of giraffes” Charles Darwin’s Theory of Evolution Galapagos Islands a. Darwin’s finches Origin of Species by Natural Selection – by Charles Darwin Evolution – concept that species have changed over time Natural Selection “organisms best suited to their environment reproduce more successfully than other organisms” 1. Adaptation 2. Fitness -competition *selection conditions change as the demands of the environment change *if environmental change is too extreme, populations cannot adapt quickly enough and they become extinct Patterns of Evolution Genetic Drift – the alteration of allele frequencies by chance events Punctuated Equilibrium – speciation occurs during brief periods of rapid genetic change Divergent Evolution – two or more related populations or species become more and more dissimilar - domestic dogs Convergent Evolution – 2 organisms seem to be similar but are not at all - shark and porpoise Co-Evolution – 2 species evolve together - plants and the animals that pollinate them Evidence of Evolution Evidence from Living Organisms Homologous and Analogous Structures a. Homologous – similar features that originated in a shared ancestor b. Analogousfeatures serve identical functions and look somewhat alike Vestigial Organs “useless features” a. appendix b. human tailbone DNA and Chemical Studies a. human and chimp DNA – very similar Embryo studies a. all vertebrae embryos are similar at 4 weeks b. all vertebrates have gill slits at 4 weeks Types of Natural Selection Stabilizing Selection * individuals with average form of a trait have the highest fitness most common Directional Selection * individuals that display a more extreme form of a trait have greater fitness than individuals with an average form of trait Disruptive Selection * individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait