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15-3 Darwin Presents His Case Inherited Variation and Artificial Selection Inherited Variation and Artificial Selection Members of each species vary from one another in important ways. In Darwin’s day, variations were thought to be unimportant, minor defects. Variations were inherited and therefore passed on. Darwin argued that this variation mattered. Slide 1 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Inherited Variation and Artificial Selection Darwin noted that plant and animal breeders would breed only the largest hogs, the fastest horses, or the cows that produced the most milk. Darwin termed this process artificial selection. Slide 2 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Slide 3 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Publication of On the Origin of Species Darwin said that what ever farmers are doing must work the same way in nature, by itself. • proposed a mechanism for evolution called natural selection: process by which individuals that are better suited to their environment survive and reproduce most successfully. • presented evidence that evolution (change in a kind of organism over time) has been taking place for millions of years—and continues in all living things. Copyright Pearson Prentice Hall Slide 4 of 41 15-3 Darwin Presents His Case Evolution by Natural Selection Evolution by Natural Selection Darwin compared processes in nature to artificial selection. By doing so, he developed a scientific hypothesis to explain how evolution occurs. Now, with the work of others, it is a theory: a well-tested explanation that unifies a broad range of observations. Slide 5 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection The Struggle for Existence Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources. Remember back to ecology in first semester: Density dependent limiting factors and what organisms compete for: Slide 6 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection The struggle for existence means that members of each species compete regularly to obtain food, living space, and other necessities of life. The struggle for existence was central to Darwin's theory of evolution. Slide 7 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection How is natural selection related to a species' fitness? Slide 8 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection Survival of the Fittest The ability of an individual to survive and reproduce in its specific environment is fitness. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival; NOT something learned within an organisms lifetime. Slide 9 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection Successful adaptations means organisms are better suited to their environment and better able to survive and reproduce. Individuals with characteristics that are not well suited to their environment either die or leave few offspring. Individuals that are better suited to their environment survive and reproduce most successfully. Darwin called this process survival of the fittest. Slide 10 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Darwin’s tenets: OVERPRODUCTION: Organism’s produce more offspring than their environment can support. Why? HERITABLE VARIATION: Offspring vary in their appearance and function, some of these variations are heritable. COMPETITION: Offspring must compete for survival, food and mates (reproduction), living space, etc. SURVIVAL OF THE FITTEST: Offspring who have the highest fitness for their environment will live longer and leave more offspring than those less suited for the environment. Slide 11 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment. Slide 12 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Slide 13 of 41 Copyright Pearson Prentice Hall 15-3 Darwin Presents His Case Evolution by Natural Selection Descent With Modification Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. Each living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification. Decent w/ modification implies relatedness. This is Slide known as common decent. 14 of 41 Copyright Pearson Prentice Hall 15-3 Click to Launch: Continue to: - or - Slide 15 of 41 Copyright Pearson Prentice Hall 15-3 Differences among individuals of a single species are referred to as a. artificial selection. b. genetic variation. c. survival of the fittest. d. environmental adaptation. Slide 16 of 41 Copyright Pearson Prentice Hall 15-3 Changes that increase a species' fitness in its environment over time are due to a. the principle of common descent. b. the geographic distribution of that species. c. natural selection. d. habitat selection. Slide 17 of 41 Copyright Pearson Prentice Hall 15-3 An inherited characteristic that increases an organism's chance of survival is called a(an) a. homologous structure. b. vestigial organ. c. adaptation. d. analogous structure. Slide 18 of 41 Copyright Pearson Prentice Hall 15-3 Evidence used by Darwin to support the idea of evolution included all the following EXCEPT a. fossils that demonstrate change over time. b. the genetic mechanism by which useful traits are inherited. c. the geographic distribution of living things. d. the presence of many homologous structures in plants and animals. Slide 19 of 41 Copyright Pearson Prentice Hall END OF SECTION