selectionoutline - Natural Selection: Darwin's Four...

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Darwinian Natural Selection Natural Selection: Darwin's Four Postulates ! Natural selection is a logical outcome of four postulates: Individuals within species are variable. Some of the variation is heritable and passed to offspring. In every generation, more offspring are produced than can survive. Survival and reproduction of individuals is not random, but depends on the variations expressed by individuals. Those with the most favorable variation tend to reproduce more and leave more individuals in the next generation. The Postulates Make Falsifiable Predictions ! There should be relatively large amounts of genetic variation present in species. ! Genetic variation should be heritable. ! Under normal circumstances, not all individuals should survive to sexual maturity and reproduction ! Reproductive success should be non-random, that is, certain specific traits should be correlated to reproductive success. Evolutionary Change ! If these conditions are met the allele frequencies in the population will change from one generation to the next. ! The alleles responsible for reproductive success should increase in frequency within the population.
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Darwinian Fitness ! Darwinian fitness is the relative ability of an individual organism to leave offspring in the next generation. ! In class, we'll talk about relative fitness which is the ability of an organism (genotype) to leave offspring in the next generation when compared to the most fit genotype. Definition of Evolution ! We can define evolution as the change in the genetic structure (composition) of a population over time , which is seen as changes in the phenotypes of individuals in the population (Dobzhansky, 1951). ! More specifically we can define evolution as the change in allele frequencies of a population over time . Adaptation ! In the Darwinian sense, an adaptation is trait or characteristic which confers greater Darwinian fitness to individuals which possess the trait when compared to those which lack the trait. The Case Study
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This note was uploaded on 04/16/2008 for the course BIO 300 taught by Professor Johnson during the Spring '08 term at Central Washington University.

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selectionoutline - Natural Selection: Darwin's Four...

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