lecture 2

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)’ Years’ago’ Milions’of’years’ago’ 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’
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lecture 2 - Evolution by Natural Selection Simple Necessary...

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