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lecture 2 - Evolution by Natural Selection Simple Necessary...

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9/30/12 1 Evolution by Natural Selection: Simple Necessary Concepts • Evolution - genetic change through time • Fitness - reproductive success of an individual • Adaptation - a heritable change that becomes common or pervasive in a population or species because it increases fitness Natural selection - The process by which heritable variations that increase fitness become more prevalent in successive generations Evolution by natural selection - requires heritable variation that affects fitness The Origin of Species Darwin developed two main ideas – Evolution explains life’s unity and diversity – Natural selection is a cause of adaptive evolution Descent with Modification The phrase descent with modification – States that all organisms are related through descent from an ancestor that lived in the remote past – Defines what Evolution is, heritable change through time.
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9/30/12 2 In the Darwinian view, the history of life is like a tree with multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms. This view explains the hierarchical relationships in Linnaean classification. Figure 22.7 Hyracoidea (Hyraxes) Sirenia (Manatees and rela:ves) Yearsago Millionsofyearsago Deinotherium Mammut Stegodon Mammuthus Platybelodon Barytherium Moeritherium Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclo=s (Africa) Natural Selection Descent with modification, or evolution, describes the changes of organisms through time. Natural Selection is one mechanism of change Natural Selection is the process that leads to adaptation
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9/30/12 3 Deductive reasoning for evolution by natural selection Observation #1: For any species, population sizes would increase exponentially – If all individuals that are born reproduced successfully – This is the argument of ? A Lyell B Cuvier C Copernicus D Malthus E Darwin Figure 22.8 Observation #2: Nonetheless, populations tend to be stable in size Observation #3: Resources are limited – Inference #1: Production of more individuals than the environment can support Leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving This is the inference Darwin arrived at after reading Malthus. Observation #4: Members of a population vary extensively in their characteristics No two individuals are exactly alike Figure 22.9
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9/30/12 4 Observation #5: Much of this variation is heritable – Experiments in plant and animal breeding prove this. Inference #2: Survival may depend in part on inherited traits – Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Figure 22.10 Terminal bud Lateral buds Brussels sprouts Cabbage Flower cluster Leaves Cauliflower Flower and stems Broccoli Wild mustard Kohlrabi Stem Kale Inference #3: The unequal ability of individuals to
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