Evolution Unit: Objectives
Upon the completion of the textbook readings in Chapters 22-26 you should be able to: Chapter 22
1. Explain how the principle of gradualism and Charles Lyell's theory of uniformitarianism influenced Darwin's ideas about evolution. The basic idea of natural selection is that a population of organisms can change over the generations if individuals having certain heritable traits leave more offspring than other individuals. The result of natural selection is evolutionary adaptation, a prevalence of inherited characteristics that enhance organisms’ survival and reproduction in specific environments. -gradualism, which holds that profound change is the cumulative product of slow but continuous processes. -incorporated Hutton’s gradualism into a theory known as uniformitarianism. The term refers to Lyell’s idea that geologic processes have not changed throughout Earth’s history. Thus, for example, the forces that build mountains and erode mountains and the rates at which these forces operate are the same today as in the past. Darwin was strongly influenced by two conclusions that followed directly from the observations of Hutton and Lyell. First, if geologic change results from slow, continuous actions rather than sudden events, then Earth must be very old, certainly much older than the 6,000 years assigned by many theologians on the basis of biblical inference. Second, very slow and subtle processes persisting over a long period of time can add up to substantial change. Darwin was not the first to apply the principle of gradualism to biological evolution, however.
2. Describe Jean Baptiste Lamarck's model for how adaptations evolve. It incorporates two ideas that were popular during Lamarck’s era. The first was use and disuse, the idea that those parts of the body used extensively to cope with the environment become larger and stronger while those that are not used deteriorate. Among the examples Lamarck cited were a blacksmith developing a bigger bicep in the arm that wields the hammer and a giraffe stretching its neck to reach leaves on high branches. The second idea Lamarck adopted was called the inheritance of acquired characteristics. In this concept of heredity, the modifications an organism acquires during its lifetime can be passed along to its offspring. The long neck of the giraffe, Lamarck reasoned, evolved gradually as the cumulative product of a great many generations of ancestors stretching ever higher. 3. Describe how Charles Darwin used his observations from the voyage of the HMS Beagle to formulate and support his theory of evolution.
Darwin noted that plants and animals he studied had definite South American characteristics, very distinct from those of Europe. That in itself may not have been surprising. But Darwin also noted that the plants and animals in temperate regions of South America were more closely related to species living in tropical regions of that continent than to species in temperate regions of Europe. Furthermore, the South American fossils that Darwin found, though clearly different from modern species, were distinctly South American in their resemblance to the living plants and animals of that continent. 4. Describe how Alfred Russel Wallace influenced Charles Darwin. Wallace developed a theory of natural selection essentially identical to Darwin’s. Wallace asked Darwin to evaluate the paper and forward it to Lyell if it merited publication. Darwin complied, writing to Lyell: "Your words have come true with a vengeance ... . I never saw a more striking coincidence ... so all my originality, whatever it may amount to, will be smashed." Lyell and a colleague presented Wallace’s paper, along with extracts from Darwin’s unpublished 1844 essay, to the Linnaean Society of London on July 1, 1858. Darwin quickly finished The Origin of Species and published it the next year. Although Wallace wrote up his ideas for publication first,...
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