BIOS
W5L1 Variation & NS.pdf

There is variability in survival and reproduction and

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There is variability in survival and reproduction, and not everyone is successful 325 Natural Selection Outcome: The genetic composition of the population changes across generations Biston betularia 326 Evolution by Natural Selection Changes in the genetic composition of a population because of differences in the survivorship and/or reproduction of individuals What persists over evolutionary time are genes, not organisms Organisms can be viewed as “gene transport machines,” a genes way of making another gene Natural selection thus favors more “efficient” gene transport machines Dawkins (1976) “The Selfish Gene” However, natural selection operates on phenotypes; selection on genes is indirect Levels of selection - gene - individual - group - species - clade 327
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Natural Selection Nuances 1. Traits under selection only impact the probability of survival and reproduction 2. Selection operates directly on the phenotypes of individuals, while populations evolve across generations (the gene pool is changed) 3. Selection can operate even if the characters under selection are not heritable – but in this case, the population will not evolve 4. Natural Selection is a process composed of testable components 328 Natural Selection in Darwin’s Finches 329 Galapagos Islands & Daphne Major 330
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Individuals vary in phenotype Variation could be due to genetic factors, environmental factors, or both 331 Medium ground finch Geospiza fortis Individuals vary in phenotype Variation could be due to genetic factors, environmental factors, or both n = 751 332 G. fortis Beak depth is heritable 333
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1977: Big Drought!
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