Chapter 23

Chapter 23 - Chapter 23: Evolution by Natural Selection The...

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Chapter 23: Evolution by Natural Selection The theory of evolution by natural selection, formulated independently by Charles Darwin and Alfred Russel Wallace, explains how organisms have come to be adapted to environments ranging from artic tundra to tropical wet forest When Darwin published his theory in 1859 in a book called On the Origin of Species by Means of Natural Selection, it unleashed a firestorm of protest through Europe The theory maintained that species were immutable, or incapable of change, and thus had been unchanged since the moment of their creation 23.1 THE PATTERN OF EVOLUTION: HAVE SPECIES CHANGED THROUGH TIME? Darwin repeatedly used the phrase “descent with modification” to describe evolution By this he meant that the species existing today have descended from other, preexisting species and that species are modified or change through time This view was clearly a radical departure from the pattern of independently created and immutable species proposed by the theory of special creation Evidence for Change through Time When Darwin began his work, biologist and geologists had just begun to assemble and interpret the fossil record A fossil is any trace of an organism that lived in the past These traces range from bones and branches to shells, tracks, or impressions, and dung The fossil record consists of all fossils that have been found and described in scientific literature Initially, fossils were organized according to their relative ages This was possible because most fossils are found in sedimentary rocks, which form from sand or mud or other materials deposited at locations such as beaches or river mouths, and because sedimentary rocks are known to form in layers Fossils from rocks underneath other rocks were judged to be older than the fossils found above them They also began naming different periods of geologic time scale After the discover of radioactivity in the early 1900s, researchers used radiometric dating techniques to assign absolute ages to the relative ages in the geologic time scale Earth is about 4.6 billion years old, and the earliest signs of life appear in rocks that formed about 3.85 billion years ago Extinction In the early 19 th century, researchers began discovering fossil bones, leaves and sells that were unlike structures from any known animal or plant After Baron Georges Cuvier published a detailed analysis of an extinct species—that is, a species that no longer exists—called the Irish elk in 1812, most scientists accepted extinction as a reality Advocates of the theory of special creation argued that the fossil species were victims of the flood at the time of Noah
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Analyses of the fossil record support the claim that more species have gone extinct than exist today Transitional Form Long before Darwin published his theory, researchers reported striking resemblances between the fossils found in the rocks underlying certain regions and the living species
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This note was uploaded on 04/17/2008 for the course BIOL 202 taught by Professor Kopeny during the Spring '08 term at UVA.

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Chapter 23 - Chapter 23: Evolution by Natural Selection The...

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