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Biology Meets Metaphysics? The Causalist/Statisticalist Debate

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Over the last decade, intense debate in the philosophy of biology community has focused on the causal status of the theories of natural selection and genetic drift, and two standard positions have crystallized – the “causalist” and “statisticalist” interpretations of evolutionary theory. After a decade, the debate shows no sign of abating. It is my project here to critically evaluate the current status of these positions. The debate between causalists and statisticalists, I will argue, does not offer a profitable framework for structuring our understanding of natural selection and genetic drift in the philosophy of biology. While it it brings to the fore an issue of significant metaphysical interest, this issue is not analyzed any more readily in the biological context. Further, the debate has worked to actively drive discussion away from the uniquely biological issue it exposes: differences in our definitions of natural selection and genetic drift.

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Biology Meets Metaphysics? The Causalist/Statisticalist Debate

  1. 1. University of Notre DameProgram in the History and Philosophy of ScienceDepartment of PhilosophyBiology Meets Metaphysics?The Causalist/Statisticalist DebatePhiloSTEM-3, April 14, 2012Charles H. Pencecharles@charlespence.net
  2. 2. The Big Picture• A large and contested debate in the philosophy of biology
  3. 3. The Big Picture• A large and contested debate in the philosophy of biology• Two factual goals:• What’s it about, and what’s the common ground?
  4. 4. The Big Picture• A large and contested debate in the philosophy of biology• Two factual goals:• What’s it about, and what’s the common ground?• What’s really at stake?
  5. 5. The Big Picture• A large and contested debate in the philosophy of biology• Two factual goals:• What’s it about, and what’s the common ground?• What’s really at stake?• Two normative claims:• The debate has focused on a general metaphysical issuethat is neither more readily solved in the biological contextnor sheds new light on biological questions
  6. 6. The Big Picture• A large and contested debate in the philosophy of biology• Two factual goals:• What’s it about, and what’s the common ground?• What’s really at stake?• Two normative claims:• The debate has focused on a general metaphysical issuethat is neither more readily solved in the biological contextnor sheds new light on biological questions• The biologically interesting issue raised has been mostlyignored
  7. 7. Common Ground• Individual-level events: causal
  8. 8. Common Ground• Individual-level events: causal• X has offspring, X dies of malnutrition, X is eaten by apredator
  9. 9. Common Ground• Individual-level events: causal• X has offspring, X dies of malnutrition, X is eaten by apredator• Theoretical apparatus for describing selection and drift:statistical
  10. 10. Common Ground• Individual-level events: causal• X has offspring, X dies of malnutrition, X is eaten by apredator• Theoretical apparatus for describing selection and drift:statistical• Selection coefficients, fitness values, broad-senseheritabilities
  11. 11. Two Major Issues1. What’s the relationship between individual-level eventsand the statistical descriptions of selection and drift?
  12. 12. Two Major Issues1. What’s the relationship between individual-level eventsand the statistical descriptions of selection and drift?2. How should we define selection and drift?
  13. 13. EpiphenomenalismBrain-Level Cause Effect
  14. 14. EpiphenomenalismBrain-Level Cause EffectBrain-Level CauseBrain-Level Cause
  15. 15. EpiphenomenalismBrain-Level Cause EffectBrain-Level CauseBrain-Level CauseAnger
  16. 16. EpiphenomenalismBrain-Level Cause EffectBrain-Level CauseBrain-Level CauseAnger?
  17. 17. Epiphenomenalism in SelectionIndividual-Level Cause Population-Level EffectIndividual-Level CauseIndividual-Level CauseNatural Selection?
  18. 18. What’s Wrong?• No engagement with biology in this debate
  19. 19. What’s Wrong?• No engagement with biology in this debate• Arguments: coin flips, race cars, apple carts, etc.
  20. 20. What’s Wrong?• No engagement with biology in this debate• Arguments: coin flips, race cars, apple carts, etc.• Impact on our understanding of how selection and driftwork not explored
  21. 21. What’s Wrong?• No engagement with biology in this debate• Arguments: coin flips, race cars, apple carts, etc.• Impact on our understanding of how selection and driftwork not explored• Obscures the fact that we disagree on the definitions ofnatural selection and genetic drift• Makes the question overall that much more difficult toanswer
  22. 22. Process vs. Product• Are selection and drift processes, or outcomes (products)?
  23. 23. Process vs. Product• Are selection and drift processes, or outcomes (products)?• Causalists: selection and drift*are processes
  24. 24. Process vs. Product• Are selection and drift processes, or outcomes (products)?• Causalists: selection and drift*are processes• Statisticalists: selection and drift are outcomes
  25. 25. The Definitions• Selection as a process: Natural selection is a samplingprocess that discriminates between organisms on thebasis of fitness (or merely physical) differences
  26. 26. The Definitions• Selection as a process: Natural selection is a samplingprocess that discriminates between organisms on thebasis of fitness (or merely physical) differences• Selection as an outcome: Natural selection is whathappens when there is a population change that ispredicted and explained by trait fitness
  27. 27. The Definitions• Selection as a process: Natural selection is a samplingprocess that discriminates between organisms on thebasis of fitness (or merely physical) differences• Selection as an outcome: Natural selection is whathappens when there is a population change that ispredicted and explained by trait fitness• Drift as a process: Genetic drift is a sampling process thatdoes not discriminate between organisms on the basis offitness differences
  28. 28. The Definitions• Selection as a process: Natural selection is a samplingprocess that discriminates between organisms on thebasis of fitness (or merely physical) differences• Selection as an outcome: Natural selection is whathappens when there is a population change that ispredicted and explained by trait fitness• Drift as a process: Genetic drift is a sampling process thatdoes not discriminate between organisms on the basis offitness differences• Drift as an outcome: Genetic drift is what happens when apopulation outcome deviates from our expectations(which are set by trait fitness values)
  29. 29. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):
  30. 30. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation
  31. 31. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation• Sampling of gametes to form offspring (in sexualorganisms)
  32. 32. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation• Sampling of gametes to form offspring (in sexualorganisms)• Splitting of recently-isolated breeding groups (withoutregard to traits, a.k.a the founder effect)
  33. 33. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation• Sampling of gametes to form offspring (in sexualorganisms)• Splitting of recently-isolated breeding groups (withoutregard to traits, a.k.a the founder effect)• More broadly: Wright’s shifting-balance theory
  34. 34. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation• Sampling of gametes to form offspring (in sexualorganisms)• Splitting of recently-isolated breeding groups (withoutregard to traits, a.k.a the founder effect)• More broadly: Wright’s shifting-balance theory• The definitions again:• Drift as a process: Genetic drift is a sampling process thatdoes not discriminate between organisms on the basis offitness differences• Drift as an outcome: Genetic drift is what happens when apopulation outcome deviates from our expectations (whichare set by trait fitness values)
  35. 35. Drift as Process and Outcome• Processes that don’t discriminate between organisms onthe basis of fitness differences (see Beatty, 1992):• Neutral genetic variation• Sampling of gametes to form offspring (in sexualorganisms)• Splitting of recently-isolated breeding groups (withoutregard to traits, a.k.a the founder effect)• More broadly: Wright’s shifting-balance theory• The definitions again:• Drift as a process: Genetic drift is a sampling process thatdoes not discriminate between organisms on the basis offitness differences• Drift as an outcome: Genetic drift is what happens when apopulation outcome deviates from our expectations (whichare set by trait fitness values)
  36. 36. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:
  37. 37. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:• Doesn’t seem to be biological
  38. 38. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:• Doesn’t seem to be biological• Doesn’t tell us anything about selection and drift
  39. 39. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:• Doesn’t seem to be biological• Doesn’t tell us anything about selection and drift• There’s also a difference between process and productnotions of selection and drift. This issue:
  40. 40. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:• Doesn’t seem to be biological• Doesn’t tell us anything about selection and drift• There’s also a difference between process and productnotions of selection and drift. This issue:• Is genuinely biological
  41. 41. Where does that Leave Us?• The causalist/statisticalist debate has focused primarily onthe issue of epiphenomenalism in selection and drift. Butthis issue:• Doesn’t seem to be biological• Doesn’t tell us anything about selection and drift• There’s also a difference between process and productnotions of selection and drift. This issue:• Is genuinely biological• Points us to interesting (and real-world!) corner caseswhere these two definitions come apart
  42. 42. ..Questions?charles@charlespence.net

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