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Evolutionary biologists

Decent with Modification

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Chapter 22: Descent with Modification: Darwinian View of Life?Lecture Outline 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: Today?s organisms descended from ancestral species that were different from modern species. Natural selection provided a mechanism for this evolutionary change. 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.

natural selection

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Natural selection is one of the basic mechanisms of evolution, along with mutation, migration, and genetic drift. Darwin's grand idea of evolution by natural selection is relatively simple but often misunderstood. To find out how it works, imagine a population of beetles: There is variation in traits. For example, some beetles are green and some are brown. There is differential reproduction. Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. There is heredity. The surviving brown beetles have brown baby beetles because this trait has a genetic basis. End result:
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