Evolution 2 - But HOW did organisms change through time? 1....

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1 But HOW did organisms change through time? 1. Darwin had the idea of evolution in 1837, long before he knew what caused it… (ie, for a long time he had no “mechanism”) 2. A mechanism occurred to him not because of Galapagos, but because he (and Mom) were pigeon breeders in England… The work of breeders suggested: ¾ That organisms change over time by the “steady accumulation of slight successive changes” that occur naturally… Common ancestor From a common ancestor… Breeders selected for English Fantail selected for distinctive traits, giving rise to literally dozens of “breeds” See purebredpigeon. com English Pouter English Carrier
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2 What causes the modification? Common ancestor Consider the Dachsund (studied after Darwin but shows the point well) “steady accumulation of slight successive changes” Almost all food service vegetables!
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3 If people select, then why can’t nature?? But what, in nature, causes the “steady accumulation” of slight changes? Darwin’s epiphany: reading Thomas Malthus
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4 “Doctrine of Malthus” “…the rule that every organic being naturally increases at so high a rate that, if not destroyed, the earth would soon be covered by the progeny of a single pair.” (Darwin 1859: 64)
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Evolution 2 - But HOW did organisms change through time? 1....

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