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Ch23Lecture_posted - 23 23 The Mechanisms of Evolution The...

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1 23 The Mechanisms of Evolution 23 2 The Mechanisms of Evolution • Charles Darwin’s Theory of Evolution • Genetic Variation within Populations • The Hardy –Weinberg Equilibrium • Evolutionary Agents and Their Effects • The Results of Natural Selection • Assessing the Costs of Adaptations • Maintaining Genetic Variation • Constraints on Evolution • Cultural Evolution • Short-Term versus Long-Term Evolution 23 3 Charles Darwin’s Theory of Evolution • Darwin was a student at Cambridge University (studying to be a clergyman) when his botany professor recommended him for a position as the ship’s naturalist on the H.M.S. Beagle , which was preparing to sail around the world. • Observations made on this trip helped Darwin formulate his theory of evolution, which had two major components. § First, species are not immutable, but change, or adapt, over time. § Second, the agent that produces the changes is natural selection.
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2 Figure 23.1 Darwin and the Voyage of the Beagle (Part 2) 23 5 Charles Darwin’s Theory of Evolution • Darwin observed that slight variations among individuals can significantly affect the chance that a given individual will survive and the number of offspring it will produce. • Darwin called this differential reproductive success of individuals natural selection . 23 6 Charles Darwin’s Theory of Evolution • Darwin clearly understood a fundamental principle of evolution—that populations, not individuals, evolve and become adapted to the environments in which they live. • The term “adaptation” has two meanings in evolutionary biology. § The first meaning refers to the processes by which adaptive traits are acquired (evolutionary mechanisms that produce them). § The second meaning refers to the traits that enhance the survival and reproductive success of their bearers (e.g., wings are an adaptation for flight).
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3 23 7 Charles Darwin’s Theory of Evolution • When Darwin proposed his theory, he had no examples of selection operating in nature and knew nothing of the mechanisms of heredity. • The rediscovery of Gregor Mendel’s publications gave rise to the study of population genetics which provides a major underpinning for Darwin’s theories. • Population geneticists apply Mendel’s laws to entire populations. • Population geneticists study variation within and among species in order to understand the processes that result in evolutionary changes in species through time. 23 8 Genetic Variation within Populations • For a population to evolve, its members must possess heritable, genetic variation, which is the raw material on which agents of evolution act. • We observe phenotypes in nature, the physical expressions of genes (but influenced by environment). • The genetic constitution that governs a trait is
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This note was uploaded on 11/07/2009 for the course FIN 300 taught by Professor Olander during the Fall '08 term at ASU.

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Ch23Lecture_posted - 23 23 The Mechanisms of Evolution The...

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