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EVOLUTION/LECTURE1 file:///E|/CH3-DARWIN-SPRING-2008/CHAPT3DARWIN_SPR_2008.html[12/8/2011 2:24:30 PM] Evolution ( PCB 4674 ). Chapter 3. Darwinian natural selection Main topics of lecture: I: Natural Selection: Darwin's four postulates 1.- Introduction 2.- The evolution of beak shape in Galápagos finches 3.- The nature of natural selection II: The evolution of Darwinism 4.- Main initial problems of Darwinism 5.- The modern synthesis I: Natural Selection: Darwin's four postulates 1.- Introduction 1.1.- Natural selection is the logical outcome of four postulates, which Darwin laid out in his introduction to "On the origin of species by means of natural selection" (published in 1859). He considered the rest of the book "one long argument" in their support. The four postulates are as follows: (1) Individuals within species are variable (2) Some of these variations are passed on to offspring (3) In every generation, more offspring are produced than can survive (4) The survival and reproduction of individuals are not random: Individuals who survive and go on to reproduce are those with the most favorable variation . They are naturally selected 1.2.- The main consequence of these four postulates is that the characteristics of populations change from one generation to the next. As a result, the characteristics of the population will change slightly with each succeeding generation. This is Darwinian evolution: gradual change in populations over time 1.3.- Darwin referred to individuals who make up a greater percentage of the population in the next generation as more fit . In doing so he introduced the concept of fitness . Darwinian fitness is the ability of an individual to survive and reproduce in its environment. Biologists use the word adaptation to refer to a trait or characteristic of an organism that increases its fitness relative to individuals without the trait. 1.4.- One of Darwin's theory of evolution is that each of the four postulates - and their logical consequence - can be verified independently. In the next section, we examine
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file:///E|/CH3-DARWIN-SPRING-2008/CHAPT3DARWIN_SPR_2008.html[12/8/2011 2:24:30 PM] each of the four postulates by reviewing and ongoing study of finches in the Galápagos Islands 2.- The evolution of beak shape in Galápagos finches 2.1.- There are 14 species of finches on the Galápagos islands. Two traits do show remarkable variation among these 14 species: the size and the shape of their beaks (Fig. 3.1). The beak is the primary tool used by birds in feeding, and the enormous range of beak morphologies reflects the diversity of foods they eat. Figure 3.1.: Phylogeny of the 14 species of Galápagos finches. The photo show the extensive variation in beak size and shape
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This note was uploaded on 01/11/2012 for the course PBC 4674 taught by Professor Ortega during the Spring '12 term at FIU.

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