(Stebbins 1971, modified by Kutschera & Niklas 1994) * * * * ? Stochasticity in Evolutionary...

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Transcript of (Stebbins 1971, modified by Kutschera & Niklas 1994) * * * * ? Stochasticity in Evolutionary...

  • Slide 1
  • (Stebbins 1971, modified by Kutschera & Niklas 1994) * * * * ? Stochasticity in Evolutionary Biology
  • Slide 2
  • When we look at the plants and bushes clothing an entangled bank, we are tempted to attribute their proportional numbers and kinds to what we call chance. But how false a view is this!
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  • the idea that chance begets order (Peirce 1893, quoted in Beatty 1984) Beatty, J. 1984. Chance and natural selection. Philosophy of Science 51:183-211. Random with respect to
  • Slide 4
  • Key insight into evolution: Particulate inheritance Deterministic effects: genes to genotypes to phenotypes
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  • FisherWright Haldane Particulate Inheritance (Mendel) + Evolution by Natural Selection (Darwin) = The Modern Synthesis Population genetics theory built from scratch 4 processes: Drift (N), Mutation ( ), Gene Flow (m), Selection (s) Consensus on theoretical possibilities, and the right model structure Disagreement on the relative importance of different processes in Nature
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  • The Evolutionary Modern Synthesis (Stebbins 1971, modified by Kutschera & Niklas 1994) * * * * ? * Processes with stochastic elements Consensus on theoretical possibilities, and the right model structure Disagreement on the relative importance of different processes in Nature
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  • The Molecular Revolution: Evolution at the level of proteins/DNA
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  • Why so much variation? Shouldnt it get edited out by natural selection? Mootoo Kimura Maybe much of this variation isnt even seen by natural selection The neutral theory of molecular evolution: Mutation, Drift, Gene flow Many DNA changes do not alter the amino-acid composition of a protein Some (many?, few?) amino acid substitutions dont alter the function of a protein
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  • Each one of these loci (some neutral, some not) has the exact same demographic history (i.e., drift, migration) The neutral theory of molecular evolution is operational (in a way that the ecological theory is not)
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  • The neutral theory of molecular evolution is operational An example: Selective sweeps
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  • Okay, so all these processes are happening in Nature but what is their relative importance? Does the answer really matter?
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  • Beatty, J. 1984. Chance and natural selection. Philosophy of Science 51:183-211. On relative importance:
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  • Beatty, J. (1997) Why do biologists argue like they do? 64:S432-S443. The importance (or not) of debates about relative importance
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  • The reason evolutionary biology seems to rest on more solid theoretical footing than ecology, is because evolutionary biologists agree on the theoretical framework, not the relative importance of different processes.
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  • Regional community Dispersal Speciation Drift Selection Dispersal Local Community Speciation Drift Selection Dispersal Global community Dispersal Speciation Drift Selection Note: Extinction results from drift & selection Everything you need to know about ecological communities
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  • The Tree of Life Project http://tolweb.org/tree/ Darwins first phylogeny What about macroevolution?
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  • A critique of assuming determinism Stephen J. Gould and contingency A critique of assuming gradualism
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  • Replaying Lifes Tape I call this experiment replaying lifes tape. You press the rewind buttongo back to any time and place in the pastThen let the tape run again and see if the repetition looks at all like the original any replay of the tape would lead evolution down a pathway radically different from the road actually taken Contingency (= stochasticity?)
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  • Are the shapes of phylogenies different from random expectation?
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  • Looks like we got null models from evolution too (in addition to neutral models)
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  • Lessons for Community Ecology: Can neutral theory be operationalized? Perhaps we can at least agree on a conceptual framework (mine, of course) Can we skip past the mind-numbingly obvious aspects of the selection-neutrality debate? Where is the relative importance approach going to get us? Building models and empirical studies to be more comparable to one another. Getting drift into models of selectionto come next week