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Evolution & Natural Selection First thoughts on the idea… • “Acquired Traits” • Once a structure is modified it is passed onto offspring Lamark Charles Darwin Thoughts (Galapagos Islands) • Evolution occurs – Change over time • Evolution is due to Natural Selection Darwin’s Finches • Finches had different beaks that were specialized for what they ate – Each had their own NICHE • All of these finches were descendents of the same finch What is Evolution? • Gradual change over time • Descent with modifications Cladogram – Newer forms (in fossils) are the modified descendants of older species Natural Selection • Organisms with favorable traits reproduce more than those with out these traits • Traits = Variation = MUTATIONS Variation / Diversity • Slight differences in the appearance of organisms (phenotypes) – Sexual reproduction – Gene recombination • IMPORTANT: if environment changes SOME organisms will survive What determines Natural Selection? • ENVIRONMENT • In order to be beneficial the trait must help the organism live in its environment • Based on phenotypes Adaptation & Fitness • Adaptation – increasing # of favorable traits • Fitness – An organisms genetic contribution to offspring • High fitness = well adapted Natural Selection & Genetic Change • Natural selection can not occur without genetic variation • Organisms that have beneficial traits will pass those traits to their offspring Fitness & Genes • Each generation has more individuals with the genes that make them “fit” • The frequency of these alleles increases over time Competition • Because resources (food, space…) are limited, organisms compete for them • Only the most fit will compete successfully and reproduce Lethal Genes • Genes that cause death • How can these genes exist? • Heterozygous individuals keep these genes in the gene pool – Total genetic info in population