Chapter 22 - CHAPTER 22 - DESCENT WITH MODIFICATION: A...

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CHAPTER 22 - DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE Introduction On November 24, 1959, Charles Darwin published On the Origin of Species by Means of Natural Selection . Darwin’s book drew a cohesive picture of life by connecting what had once seemed a bewildering array of unrelated facts. Darwin made two points in The Origin of Species : Today’s organisms descended from ancestral species. Natural selection provided a mechanism for evolutionary change in populations. A. Historical Context for Evolutionary Theory 1. Western culture resisted evolutionary views of life The Origin of Species challenged a worldview that had been accepted for centuries. The key classical Greek philosophers who influenced Western culture, Plato and Aristotle, opposed any concept of evolution. Plato believed in two worlds: one real world that is ideal and perfect and an illusory world of imperfection that we perceive through our senses. Aristotle believed that all living forms could be arranged on a ladder ( scala naturae ) of increasing complexity with every rung taken with perfect, permanent species. The Old Testament account of creation fortified the idea that species were individually designed and did not evolve. In the 1700s, the dominant philosophy, natural theology , was dedicated to studying the adaptations of organisms as evidence that the Creator had designed each species for a purpose. At this time, Carolus Linnaeus, a Swedish botanist, developed taxonomy , a system for naming species and grouping species into a hierarchy of increasingly complex categories. Darwin’s views were influenced by fossils , the relics or impressions of organisms from the past, mineralized in sedimentary rocks . Sedimentary rocks form when mud and sand settle to the bottom of seas, lakes, and marshes. New layers of sediment cover older ones, creating layers of rock called strata. Fossils within layers show that a succession of organisms have populated Earth throughout time. Paleontology , the study of fossils, was largely developed by Georges Cuvier, a French anatomist. In particular, Cuvier documented the succession of fossil species in the Paris Basin. Cuvier recognized that extinction had been a common occurrence in the history of life. Instead of evolution, Cuvier advocated catastrophism , that boundaries between strata were due to local flood or drought that destroyed the species then present. Later, this area would be repopulated by species immigrating from other unaffected areas. 2. Theories of geologic gradualism helped clear the path for evolutionary biologists In contrast to Cuvier’s catastrophism, James Hutton, a Scottish geologist, proposed that the diversity of landforms (e.g., canyons) could be explained by mechanisms currently operating. Hutton proposed a theory of
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Chapter 22 - CHAPTER 22 - DESCENT WITH MODIFICATION: A...

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