NAU BIO 435 - The nature of natural selection (19 pages)

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The nature of natural selection



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The nature of natural selection

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Pages:
19
School:
Northern Arizona University
Course:
Bio 435 -

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The nature of natural selection 10 New traits can evolve although natural selection acts on existing traits the Panda s thumb feathers bird wings Long term directional selection can produce phenotypes that are far outside the phenotypic range of an ancestral population Beak length in soapberry bugs Oil content in corn Illinois corn oil experiment These responses are due to the accumulation of favorable alleles at several to many loci in the same individuals and to the occurrence of favorable chance mutations during the course of selection 1 The panda s thumb 2 Oil content of corn 3 Objections to Darwinism Blending inheritance Natural selection can t produce evolutionary change because new favorable variations will be blended out when individuals that carry them mate with individuals that don t This objection was raised at least as early as 1867 It reflects the fact that nobody except Mendel had an understanding of genetics Darwin could not explain how new variations arise Again he didn t know any genetics and therefore did not have a mechanistic understanding of mutation 4 Objections to Darwinism Age of the earth The earth isn t old enough and the window of time during which temperatures on the earth have been suitable for life is too narrow This objection goes back to calculations by Lord Kelvin a prominent 19th British physicist that placed the age of the earth at 15 20 Myr Kelvin assumed that the earth was simply gradually losing its initial heat by radiation into space 5 Objections to Darwinism Origin of complex adaptations pt 1 The problem of incipient adaptations or unfit intermediate stages The vertebrate eye is a complex highly integrated structure variable focal length image forming lens retina iris cornea muscles for moving eye etc If any of those is missing or imperfectly formed vision may be absent or seriously impaired If eyes evolved gradually then the intermediate stages could not have functioned as today s eyes do and would not have conferred a



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