@glipsnort
@Eddie
@Jon_Garvey
@Chris_Falter
@Jonathan_Burke
I haven’t commented here for a while, but I have caught up on most of the comments, and I think I see a pattern that might be worth mentioning.
The argument seems to boil down to whether or not its possible to predict the results of natural selection, without a priori (or a posteriori for that matter) knowledge of some quantitative estimate of fitness (which I think Steve has pretty well defined).
The answer is no, for the reason that Steve has given, it is extremely difficult to make accurate predictions in very complex scenarios. Since all of biology sets the standard for complexity among the sciences, it isn’t surprising that the central theory of biology, evolution by natural selection, would suffer from this problem. But biology is not alone. The three body problem in physics suffers similarly, and the solution of the Schrodinger equation for elements much larger than hydrogen does also.
This lack of predictability is not a hallmark of a bad science. The old idea that science always makes testable predictions has been modified greatly over the past century, ever since the uncertainty principle showed that in some cases, non-predictability is the rule. Chaos theory treats the idea of non-predictability in mathematical terms, and demonstrates its application to a large number of deterministic processes throughout the physical and social sciences.
So what all of this means is that yes, natural selection is a highly complex phenomenon whose outcomes cannot be predicted on empirical grounds based on quantitative assessments of fitness measures. But, again as Steve has shown, this doesn’t mean that such measures don’t exist, both absolute and relative fitness can be measured quantitatively and used in population genetics and Hardy Weinberg calculations to make useful predictions about how evolution works.
Here is an illustration from my own work. My group discovered a new allele of a human metabolic gene. We assessed its frequency in several populations. We found that it followed Hardy Weinberg equilibrium, which implied that it was not undergoing natural selection. We therefore predicted that it might not have any effect on fitness. After some further study, we found that indeed, as predicted, this allele had no effect on the health of the population (because of the activity of the gene in question, we thought it might)… So, while we never actually measured the fitness of the allele, the genotype, or the phenotype of the people who had the allele, it was still possible to make predictions about its role in natural selection based on biological law.