Among philosophers, controversy over the notion of drift in population genetics is ongoing. This is at least partly because the notion of drift has an ambiguous usage among population geneticists. My goal in this paper is to explicate the causal dimension of drift, to say what causal influences are responsible for the stochasticity in population genetics models. It is commonplace for population genetics to oppose the influence of selection to that of drift, and to consider how the dynamics of populations are altered when each has greater or lesser influence. I define the causes that are referred to as drift when researchers speak this way.

  1. Introduction

  2. Populations and Variant Types

  3. The Cause–Effect Ambiguity of Drift

  4. Non-directional Factors in Population Genetics

  5. How Nev Is Used in Population Genetics

  6. Causal Conceptions of Drift

    • 6.1

      The Millstein/Beatty conception of drift

    • 6.2

      Rosenberg and Bouchard: Drift as initial conditions

  7. NINPICs

    • 7.1

      Why drift is instituted by NINPICs

    • 7.2

      How NINPICS work

    • 7.3

      NINPICs and random sampling

    • 7.4

      Independent sampling and effective population size

    • 7.5

      Variance in progeny number

    • 7.6

      Population effects of NINPICs

  8. NINPICs and the Stochastic Character of Selection Theory

  9. Conclusion


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