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Transcript
16.3 Describe the condition under which natural selection occurs. Explain the principle of common descent. • Malay Archipelago • Darwin and himself both read Malthus essay • Wrote to Darwin in 1858 and explained his idea of “Survival of the Fittest” • Gave Darwin confidence to publish his book in 1859 1. Struggle of Existence - competition for food and living space is a part of life 2. Variation and Adaptation - some variations better suited for environment - inheritable traits that increase ability to survive and reproduce called adaptations Monarch Viceroy 3. Survival of the Fittest - adaptations affect fitness - fitness is how well an organism survives and reproduces in its environment - better adaptations = higher fitness 4. Natural Selection - Process by which organisms with variations best suited for environment will survive and leave more offspring - environment influences fitness - Process does not make organisms “better” and does not act in a fixed direction For Natural Selection to occur, three criteria must be met: 1. Variation 2. Differential reproductive success (fitness) 3. Heritability - genes (unit of evolution) passed to offspring ◦ Under what conditions does natural selection occur? ◦ Natural selection occurs in any situation in which more individuals are born than can survive (the struggle for existence), there is natural heritable variation (variation and adaptation), and there is variable fitness among individuals (survival of the fittest). Evolution by Natural Selection • descent with modification - traits modified gradually in species from a common ancestor - happens over LONG periods of time • all species, living and extinct, are descended from ancient common ancestors Morphological – organisms structure Behavioral – how the organism acts Physiological – functions of organism http://wildamerica.com/videos/transcripts /s34.html “Designs for Defense” (VHS clip)