Problems with adaptationism.

In Uncategorized on March 2, 2010 by toddallinmorman

In another thread as an aside I called adaptationism ‘silly.’ I did not go into the details because the thrust of the thread was on models and explanation and my opinion of adaptationism was not pertinent, but I included the editorialization nonetheless. Here is a more substantive presentation. S&O define the adaptationist hypothesis as: Natural selection is a sufficient explanation for most nonmolecular traits and these traits are locally optimal. I think B&R do a fine job at demonstrating the problems. The proposition assumes optimality. The term ‘most’ is unclear and ill defined. The notion of ‘sufficient’ is unclear. Optimality is defined as simply having a higher fitness by S&O, but elsewhere it has been implied that optimality creates something of a steady state of dominance, “As a results other phenotypes are eliminated from the population (or nearly so) or prevented from invading.” (internal citations omitted, S&O p.362.) Sufficiently is alleged to be confirmed by a ‘censored’ by an optimality model (note optimality is now being assumed), “Natural selection here provides a sufficient explanation because taking other factors into account could not significantly enhance the predictive accuracy of the optimality.” (S&O 363.) I already ranted a bit about ‘most’ before in the original thread, but to add to that, if most means barely more than half, this hypothesis seems fairly uninteresting. About half the time the hypothesis wont be true in such an instance. In addition, confirmation is alleged to come from a model, of whose accuracy we cannot independently verify, that does not ‘significantly’ differ from the ‘optimality’. But, optimality was previously defined as simply being the most fit trait, so how can one significantly differ (the question is either/or)? S&O must mean that the prediction of the model for fitness must not be ‘significantly’ enhanced by containing the relevant factors. While ‘optimality’ in the first definition is trivially verifiable as it does not have degrees, optimality models appear to provide projections as to the actual fitness. Thus S&O must be arguing that the model does not differ significantly from another model’s predictions. But what if both models are wildly inaccurate? B&R modify S&O to take care of some of these difficulties and make the adatationist hypothesis a two part hypothesis: Natural Selection is the sole process involved in the evolution of T (from some point at time at which all of the relevant variants exist in the relevant lineage). AND T is locally optimal. (B&R 192) This is a vast improvement over S&O, but by couching this in terms of evolution (here meaning the change in fitness and thus a change in relative preponderance of trait that is represented by a real number) we are faced again with the precise value of fitness alluded to by S&O. B&R demonstrate that this hypothesis is trivially false in all cases as other factors are involved in the exact fitness of a trait and the precise fitness will be different. (See pages 196-97). This is, of course, assuming optimality, which we have no reason to assume. Please also note that adaptationism ignores mutation as the source of traits in the first place and thus only deals with a very localized place in time. It seems that adaptationism is trying to claim that natural selection (assuming optimality, which is not a fair assumption) is the cause of the fitness of a trait. Without characterizing it as the ‘primary’ cause, this is simply not true, as the fitness with only natural selection will vary. If one is simply saying natural selection is the primary cause of the current level of fitness, this seems trivially true, as it is hard to imagine a model created without natural selection that would come anywhere close in providing an accurate prediction of fitness, except in the most rare and extreme of cases. I have to run to class.

I am so sorry, the stupid cut an paste eliminated my paragraph breaks. I need to go.


One Response to “Problems with adaptationism.”

  1. I don’t know whether this adds or subtracts from the conversation to date. But I have been reading a pile of ancillary readings on game theory, dynamic programming, optimal control theory, and evolutionary game theory (back to Maynard Smith and Price). My way back out of the woods uses a flashlight from the Stanford Encyclopedia of Philosophy chapter on EGT by Jason McKenzie Alexander below:

    “There are two approaches to evolutionary game theory. The first approach derives from the work of Maynard Smith and Price and employs the concept of an evolutionarily stable strategy as the principal tool of analysis. The second approach constructs an explicit model of the process by which the frequency of strategies change in the population and studies properties of the evolutionary dynamics within that model.

    The first approach can thus be thought of as providing a static conceptual analysis of evolutionary stability. “Static” because, although definitions of evolutionary stability are given, the definitions advanced do not typically refer to the underlying process by which behaviours (or strategies) change in the population. The second approach, in contrast, does not attempt to define a notion of evolutionary stability: once a model of the population dynamics has been specified, all of the standard stability concepts used in the analysis of dynamical systems can be brought to bear.”

    We are reading type 1 papers, not type 2. I think this distinction is important when we speak of explanation relative to optimality.

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