rav65819_ch21_415-432

rav65819_ch21_415-432 - ; 21 chapter The Evidence for...

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chapter The Evidence for Evolution introduction AS WE DISCUSSED IN CHAPTER 1, when Darwin proposed his revolutionary theory of evolution by natural selection, little actual evidence existed to bolster his case. Instead, Darwin relied on observations of the natural world, logic, and results obtained by breeders working with domestic animals. Since his day, however, the evidence for Darwin’s theory has become overwhelming. The case is built upon two pillars: first, evidence that natural selection can produce evolutionary change, and second, evidence from the fossil record that evolution has occurred. In addition, information from many different areas of biology—fields as different as anatomy, molecular biology, and biogeography—is only interpretable scientifically as being the outcome of evolution. concept outline 21.1 The Beaks of Darwin’s Finches: Evidence of Natural Selection Galápagos fnches exhibit variation related to Food gathering Modern research has verifed Darwin’s selection hypothesis 21.2 Peppered Moths and Industrial Melanism: More Evidence of Selection Light-colored moths decreased because oF selection by predation When environmental conditions reverse, so does selection pressure The agent oF selection may be diFfcult to pin down 21.3 Arti±cial Selection: Human-Initiated Change Experimental selection demonstrates changes in populations Agricultural selection has led to extensive modifcation oF crops and livestock Domesticated breeds have arisen From artifcial selection 21.4 Fossil Evidence of Evolution
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The age of fossils is estimated by rates of radioactive decay Fossils present a history of evolutionary change Fossils document evolutionary transitions The evolution of horses is a prime example of evidence from fossils 21.5 Anatomical Evidence for Evolution Homologous structures suggest common derivation Early embryonic development shows similarities in some groups Some structures are imperfectly suited to their use Vestigial structures can be explained as holdovers from the past 21.6 Convergent Evolution and the Biogeographical Record Marsupials and placentals demonstrate convergence Convergent evolution is a widespread phenomenon Biogeographical studies provide further evidence of evolution 21.7 Darwin’s Critics 415 rav65819_ch21_415-432.indd 415 rav65819_ch21_415-432.indd 415 1/2/07 6:29:36 PM 1/2/07 6:29:36 PM 21.1 The Beaks of Darwin’s Finches: Evidence of Natural Selection As you learned in the preceding chapter, a variety of processes can produce evolutionary change. Most evolutionary biologists, however, agree with Darwin’s thinking that natural selection is the primary process responsible for evolution. Although we cannot travel back through time, modern-day evidence confirms the power of natural selection as an agent of evolutionary change. This evidence comes from both the field and the laboratory and from both natural and human-altered situations. Darwin’s finches are a classic example of evolution by natural selection. When he visited the
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rav65819_ch21_415-432 - ; 21 chapter The Evidence for...

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