BIOL 1070 Chapter Notes - Chapter Unit 3: Genetic Drift, Gamete, Holocene Extinction

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Individuals within populations are variable. the basic postulates that darwin presented: 1: this variability among individuals is at least partly heritable. Natural selection by itself does not create new traits, it only changes the proportion of variation that is already present in the population. Most often, natural selection reduces the amount of variation in a population because some variants are eliminated: mutation, not natural selection, is the source of new variation. Natural selection is, by de nition, non-random with respect to tness. This means that, overall, it is a serious misconception to consider adaptation as happening by chance : mutations occur with all three possible outcomes: neutral (no phenotypic effect), deleterious (bad effects), and bene cial (positive effects). Bene cial mutations may be rare and deliver only a minor advantage, but these can nonetheless increase in proportion in the population over many generations by natural selection.

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