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Chapter 22 - Chapter 22 Descent with Modification Darwinian...

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Chapter 22 - Descent with Modification: Darwinian View of Life Overview: Darwin Introduces a Revolutionary Theory On November 24, 1859, 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 major points in The Origin of Species: 1. Today’s organisms descended from ancestral species that were different from modern species. 2. Natural selection provided a mechanism for this evolutionary change. o The basic idea of natural selection is that a population can change over time if individuals that possess certain heritable traits leave more offspring than other individuals. o Natural selection results in evolutionary adaptation, an accumulation of inherited characteristics that increase the ability of an organism to survive and reproduce in its environment. n Eventually, a population may accumulate enough change that it constitutes a new species. n In modern terms, we can define evolution as a change over time in the genetic composition of a population. o Evolution also refers to the gradual appearance of all biological diversity. n Evolution is such a fundamental concept that its study is relevant to biology at every level, from molecules to ecosystems. o Evolutionary perspectives continue to transform medicine, agriculture, biotechnology, and conservation biology. Concept 22.1 – The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species Western culture resisted evolutionary views of life. Darwin’s view of life contrasted with the traditional view of an Earth that was a few thousand years old, populated by life forms that were created at the beginning and had remained fundamentally unchanged. o The Origin of Species challenged a worldview that had been long accepted. The Greek philosopher Aristotle (384–322 B.C.E.) opposed any concept of evolution and viewed species as fixed and unchanging. o Aristotle believed that all living forms could be arranged on a ladder of increasing complexity (scala naturae) with perfect, permanent species on every rung. The Old Testament account of creation held that species were individually designed by God and, therefore, perfect. In the 1700s, natural theology viewed the adaptations of organisms as evidence that the Creator had designed each species for a purpose.
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Carolus Linnaeus (1707–1778), a Swedish physician and botanist, founded taxonomy, a system for naming species and classifying species into a hierarchy of increasingly complex categories. o Linnaeus developed the binomial system of naming organisms according to genus and species. o In contrast to the linear hierarchy of the scala naturae, Linnaeus adopted a nested classification system, grouping similar species into increasingly general categories.
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