rav65819_ch22_433-452

rav65819_ch22_433-452 - ; 22 The Origin of Species chapter...

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;;;;;;;; 22 The Origin of Species
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chapter introduction ALTHOUGH DARWIN TITLED HIS BOOK On the Origin of Species, he never actually discussed what he referred to as that “mystery of mysteries”—how one species gives rise to another. Rather, his argument concerned evolution by natural selection; that is, how one species evolves through time to adapt to its changing environment. Although an important mechanism of evolutionary change, the process of adaptation does not explain how one species becomes another, a process we call speciation. As we shall see, adaptation may be involved in the speciation process, but it does not have to be.
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Before we can discuss how one species gives rise to another, we need to understand exactly what a species is. Even though the definition of a species is of fundamental importance to evolutionary biology, this issue has still not been completely settled and is currently the subject of considerable research and debate. concept outline 22.1 The Nature of Species Sympatric species inhabit the same locale but remain distinct Populations of a species exhibit geographic variation 22.2 The Biological Species Concept Prezygotic isolating mechanisms prevent the formation of a zygote Postzygotic isolating mechanisms prevent normal development into reproducing adults The biological species concept does not explain all observations 22.3 The Evolution of Reproductive Isolation Selection may reinforce isolating mechanisms 22.4 The Role of Genetic Drift and Natural Selection in Speciation Random changes may cause reproductive isolation Adaptation can lead to speciation 22.5 The Geography of Speciation Allopatric speciation takes place when populations are geographically isolated Sympatric speciation occurs without geographic separation 22.6 Species Clusters: Evidence of Rapid Evolution Hawaiian Drosophila exploited a rich, diverse habitat Darwin’s nches species adapted to use different food types f Lake Victoria cichlid shes diversi ed very rapidly f f New Zealand alpine buttercups underwent speciation in glacial habitats 22.7 The Pace of Evolution
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Gradualism is the accumulation of small changes Punctuated equilibrium is long periods of stasis followed by relatively rapid change Evolution may include both types of change 22.8 Speciation and Extinction Through Time Five mass extinctions have occurred in the distant past A sixth extinction is underway 22.9 The Future of Evolution 433 rav65819_ch22_433-452.indd 433 rav65819_ch22_433-452.indd 433 12/7/06 9:36:58 AM 12/7/06 9:36:58 AM 22.1 The Nature of Species Any concept of a species must account for two phenomena: the distinctiveness of species that occur together at a single locality, and the connection that exists among different populations belonging to the same species. Sympatric species inhabit the same locale but remain distinct
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This note was uploaded on 10/15/2010 for the course BIO BIO1 taught by Professor Lipke during the Fall '09 term at CUNY Brooklyn.

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rav65819_ch22_433-452 - ; 22 The Origin of Species chapter...

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