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Darwinian Natural Selection

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McMaster University
Douglas Davidson

Darwinian Natural Selection (Pages 74 – 97) 3.1. Artificial Selection: Domestic Animals and Plants • To increase the frequency of desirable traits in their stocks, plant and animal breeders employ artificial selection (Example of Darwin and his pigeon’s on Page 74). o If the desirable traits are passed from parents to offspring, then the next generation, consisting of the progeny of only the selected mates, will show the desirable traits in a higher proportion than existed in the previous generation. o Read example of Tomato on page 74 and 75. 3.2. Evolution by Natural Selection • Darwin realized that a process like artificial selection occurs in nature • His Theory of Evolution by Natural Selection suggests that descent with modification is the logical outcome of four postulates: • Individuals within populations are variable • The variations among individuals are, at least in part, passed from parents to offspring • In every generation, some individuals are most successful at surviving and reproducing than others • The survival and reproduction of individuals are not random; instead they are tied to the variation among individuals. The individuals with the most favourable variations, those who are better at surviving and reproducing, are naturally selected. o If these four postulates are true then composition of the population changes from one generation to the next (see Figure 3.4 on page 76). o If there are differences among the individuals in a population that can be passed on to offspring, and if there is differential success among those individuals in surviving and/or reproducing, then some traits will be passed on more frequently than other. • The characteristics of a population will change slight with each succeeding generation Darwinian evolution. o Darwin referred to the individuals who are better at surviving and reproducing, and whose offspring make up a great percentage of the population in the next generation as fit: • The ability of an individual to survive and reproduce in its environment • An important aspect is its relative nature. Fitness refers to how well an individual survives and how many offspring it produces compared to others of its species. • Adaptation refers to a trait or characteristic of an organism that increases its fitness relative to individuals without the trait. • Read on Alfred Russell Wallace (Page 77) • The interesting fact is that the Darwin-Wallace theory’s four postulates and their logical consequence can be verified independently (testable). 3.3 The Evolution of Flower Color in an Experimental Snapdragon Population K.N Jones and J. Reithel (2001) did an experiment using 48 sna
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