Wednesday, June 26, 2013

Dembski’s perennial misconception of fitness

DiEb has begun a response to the latest morph of the creationist model of “search” (Dembski, Ewert, and Marks, “A General Theory of Information Cost Incurred by Successful Search” [pdf]). Here, slightly modified, is a rather general comment I made.

In the conventional “no free lunch” analytic framework, the objective (cost, fitness) function is a component of the problem. Dembski, Ewert, and Marks turn the objective function into an “oracle” that is part of the problem-solver itself. This model is inappropriate to most, if not all, of the evolutionary computations they purport to have analyzed.

Back in the 1990’s, Dembski committed himself to the misconception that Richard Dawkins’ Weasel program uses the fitness function in order to “hit the target.” Various people have tried, with no apparent success, to explain to him that one of the offspring in each generation survives because it is the most fit. The so-called target is nothing but the fittest individual.

To put it simply, the fitness function comes first. The “target” is defined in terms of the fitness function. Dembski gets this backwards. He believes that the target comes first, and that the fitness function is defined in terms of the target.

Dembski and Marks carry this to extreme in “Life's Conservation Law.” They claim that biological targets exist implicitly in nature, and that if Darwinian evolution “hits” them, then fitness functions necessarily have guided evolution. A remarkable aspect of this claim is that they treat fitness functions, which are abstractions appearing in mathematical models of evolution, as though they really exist.

The “search for a search” is another abstraction that they reify. A probability measure on the sample space is a mathematical abstraction. They merely assert that a search practitioner, in selecting a search, searches the uncountably infinite set of probability measures. To that I say, “Give me a physical description of the process.”

1 comment :

  1. IMO Dembski and Marks have a warped idea of the fitness function as they in fact don't use the output of the function, they are only interested in the elements of the search space and seem to think of a fitness function as a kind of distraction.

    In their paper for the Ithaca Conference, this becomes especially evident: at first, they are talking about the "probability of an element to be in the target", and then this morphes to their idea of a "fitness function".