genetic drift & genome architecture

Sarkar S 2015 The genomic challenge to adaptationism. Brit J Phil Sci 66:505-536.

  • the term 'adaptation' can be used to refer to a process (of adaptation), to a state of affairs (for instance, a state of adaptation to some environment), or to an entity (that is, the biological feature that is an adaptation)
  • from the perspective of this article, Lewontin ([1974]) was an advocate rather than a critic of adaptationism because he sided with the selectionists in the neutralism–selectionism debate
  • this choice makes the present critique logically stronger than that of Gould and Lewontin ([1979]) in the sense that it would accept as an adaptation any feature that is sufficiently explained by natural selection whether or not it constitutes a local optimum
  • even this weak form of empirical adaptationism is challenged by the findings of recent genomics
  • intellectually respectable evolutionary theorizing must be based on population genetics theory, which forms the substantive core of the relevant evolutionary theory
  • the mathematical theory of population genetics reduces the relevant debate to empirical questions that can be assessed on the basis of mathematical analysis and empirical data
  • the model of evolution that emerges from the core argument is not a neutral model
  • it assumes that changes in the genome are maladaptive
  • it is essentially a nearly neutral model
  • the evidence in favour of it (sketched in Section 4.1) that supported a 'mutational-hazard' model may not be applicable when genome expansion is due to ploidy change
  • as should then be no surprise, varied genome sizes occur irrespective of population size
  • many of the claims of adaptation based on sequence data suffer from a critical incompleteness
  • the fitness of the corresponding phenotypes is not independently assessed
  • Lynch (for example, [2007a], [2007b]) sometimes suggests that non-adaptationist models should be regarded as null models for (classical) statistical hypothesis testing
  • a model with no selection is simpler than a model that posits selection (which is an additional assumption)
  • the core argument and its variants offer a better explanation of genome architecture than adaptationist alternatives
  • a low effective population size (Ne) makes selection ineffective
  • thus, the claims defended in this article are stronger than the non-rejection of a null model
  • additionally, these arguments do not assume the framework of (classical) statistical hypothesis testing