3 - Descent with Modification and Population Evolution

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Descent with Modification I. Descent with Modification A. Unity of life 1. All organisms are related 2. Organisms have descended from ancestral species 3. Adaptations a. Modifications resulting over time as descendants inhabit differing environments B. Metaphor depiction of history of life—“Tree” 1. Tips are contemporary 2. Branch points represent ancestors or evolutionary lines 3. Most branch points are dead 4. Closely related organisms share recent branch points Terms and Concepts: II. Natural selection—inferences and observations A. Observations: 1. If all individuals reproduced successfully, populations would grow exponentially a. All species have a great potential fertility 2. Populations tend to remain constant a. Despite tremendous reproductive capacity, population size remains constant 3. Resources are limited B. Inference 1: Over production of individuals leads to competition for limited resources with only a limited number of individuals surviving C. Observations 1. Individual characteristics within a population vary extensively a. All individuals within a population differ 2. Variation is heritable a. Most variability can be passed to subsequent generation b. Excludes traits acquired during individuals lifetime D. Inference 2: Survival depends on the heritable constitution of surviving individuals—individuals with inherited traits best suited for their environment are more likely to produce offspring E. Inference 3: The differences in ability to survive and reproduce lead to a gradual change in a population, with favorable characteristics accumulating over generations Descent with Modifcation and Population Evolution http://www.rci.rutgers.edu/~uzwiak/GBSummer08/GB102Sum. .. 1 oF 6 7/8/08 10:03 AM
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This is Descent with Modification . The mechanism for this modification has been the cumulative effect of natural selection over extended periods of time. III. Conditions for Natural Selection A. Variation and Overproduction 1. Resources limitations usually are apparent only there is more demand than supply a. Plentiful resources exclude need for competition i. Therefore no selection 2. Without diversity, even with limiting resources, selection would not occur B. Fit genes are generally passed on 1. Over time, environment favors certain variations that promote survival a. Variations are optimal for some but not all environments i. Adaptation under one condition may be useless or even deleterious under different conditions C. Change occurs gradually—Gradualism 1. Advantages of some heritable traits are slight a. Traits accumulate over generations 2. Evolution of life did not occur rapidly with dramatic change a. Gradual accumulation of small changes D. Individuals do not evolve
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This note was uploaded on 07/19/2008 for the course BIO 102 taught by Professor Brey during the Spring '08 term at Rutgers.

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3 - Descent with Modification and Population Evolution

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