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The Conflation of “Chance” in Evolution

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Literature on the role of “chance” in evolutionary theory exhibits a dizzying array of claims – from “randomness” in genetic drift and mutation to “propensities” in fitness and “contingency” in macroevolution. I argue that much of this diversity is due to the persistent conflation of several senses of “chance,” and a corresponding failure to determine which sense is at issue in any particular biological instance. I offer an attempt to clarify and separate five of these senses: (i) the statistical or non-statistical character of a theory, (ii) the probabilistic or non-probabilistic character of a causal process, (iii) the determinism or indeterminism of underlying physics, (iv) the contingency or necessity of a historical process, and (v) the predictability or unpredictability of a particular system. I then conclude with an initial effort at showing how careful maintenance of these distinctions can enhance our understanding of the role of chance in evolution, by applying them to a few current debates in the philosophy of biology.

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The Conflation of “Chance” in Evolution

  1. 1. University of Notre DameProgram in the History and Philosophy of ScienceDepartment of PhilosophyThe Conflation of “Chance”in EvolutionISHPSSB ’11Charles H. Pencecharles@charlespence.net
  2. 2. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution
  3. 3. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:
  4. 4. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:• The philosophical debates are unresolved
  5. 5. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:• The philosophical debates are unresolved• The distinctions at work are merely semantic
  6. 6. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:• The philosophical debates are unresolved• The distinctions at work are merely semantic• Two rebuttals:
  7. 7. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:• The philosophical debates are unresolved• The distinctions at work are merely semantic• Two rebuttals:• Distinguish four notions of “chance” without resolvingthose debates
  8. 8. An Argument in Two Parts• Main Thesis: We ought to be more careful with our use ofchance in evolution• Two objections:• The philosophical debates are unresolved• The distinctions at work are merely semantic• Two rebuttals:• Distinguish four notions of “chance” without resolvingthose debates• Show that conflation causes problems in arguments
  9. 9. Four Notions of “Chance”“process” chance randomness
  10. 10. Four Notions of “Chance”“process” chance randomnesssubjective chance objective chanceunpredictability
  11. 11. Four Notions of “Chance”“process” chance randomnesssubjective chance objective chancecausal indeterminism probabilistic causal processesunpredictability
  12. 12. Four Notions of “Chance”• randomness• unpredictability• causal indeterminism• probabilistic causal processes
  13. 13. Four Notions of “Chance”• randomness• unpredictability• causal indeterminism• probabilistic causal processes• Not the only four!
  14. 14. Brandon & Carson• “The Indeterministic Character of Evolutionary Theory”(1996)
  15. 15. Brandon & Carson• “The Indeterministic Character of Evolutionary Theory”(1996)• “drift clearly is a stochastic or probabilistic orindeterministic phenomenon” (324)
  16. 16. Brandon & Carson• “The Indeterministic Character of Evolutionary Theory”(1996)• “drift clearly is a stochastic or probabilistic orindeterministic phenomenon” (324)• “if one is a realist...then one should conclude that[evolutionary theory] is fundamentally indeterministic”(336)
  17. 17. But then...• “the inferences we can make” about drift (322)• what drift “can predict” or “cannot predict” (323)
  18. 18. But then...• “the inferences we can make” about drift (322)• what drift “can predict” or “cannot predict” (323)• The “hidden variables” argument
  19. 19. But then...• “the inferences we can make” about drift (322)• what drift “can predict” or “cannot predict” (323)• The “hidden variables” argument• Response: Graves, Horan, & Rosenberg (1999)
  20. 20. A Reinterpretation• What about probabilistic causation?
  21. 21. A Reinterpretation• What about probabilistic causation?• Brandon’s causal reading of drift
  22. 22. A Reinterpretation• What about probabilistic causation?• Brandon’s causal reading of drift• Back to hidden variables
  23. 23. Conclusions• Conflations of “chance”:• BC conflate at least three senses of “chance”(unpredictability, causal indeterminism, probabilisticcausal processes)• Only on one of these does their argument go through• GHR conflate at least two senses of “chance”(unpredictability, causal indeterminism)
  24. 24. Conclusions• Conflations of “chance”:• BC conflate at least three senses of “chance”(unpredictability, causal indeterminism, probabilisticcausal processes)• Only on one of these does their argument go through• GHR conflate at least two senses of “chance”(unpredictability, causal indeterminism)• Arguments fail to engage
  25. 25. Conclusions• Conflations of “chance”:• BC conflate at least three senses of “chance”(unpredictability, causal indeterminism, probabilisticcausal processes)• Only on one of these does their argument go through• GHR conflate at least two senses of “chance”(unpredictability, causal indeterminism)• Arguments fail to engage• But the distinctions are well-known!
  26. 26. ..Questions?charles@charlespence.net

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