Wednesday, April 27, 2005

Kingsolvers Diverge Over Natural Selection

Dembski comments on a paper by . G. Kingsolver et al. in a meta-analytic statistical study titled “The Strength of Phenotypic Selection in Natural Populations,” published in the March 2001 issue of The American Naturalist.

Dembski 'argues' that “important issues about selection remain unresolved,” which ends up being a euphemistic way of saying that natural selection was found to have virtually no statistically significant effect (see here for David Berlinski’s fuller commentary).

Let’s look at the abstract…

abstract: How strong is phenotypic selection on quantitative traits in the wild? We reviewed the literature from 1984 through 1997 for studies that estimated the strength of linear and quadratic selection in terms of standardized selection gradients or differentials on natural variation in quantitative traits for field populations. We tabulated 63 published studies of 62 species that reported over 2,500 estimates of linear or quadratic selection. More than 80% of the estimates were or morphological traits; there is very little data for behavioral or physiological traits. Most published selection studies were unreplicated and had sample sizes below 135 individuals, resulting in low statistical power to detect selection of the magnitude typically reported for natural populations. The absolute values of linear selection gradients FbF were exponentially distributed with an overall median
of 0.16, suggesting that strong directional selection was uncommon. The values of FbF for selection on morphological and on life-history/ phenological traits were significantly different: on average, selection on morphology was stronger than selection on phenology/life history.
Similarly, the values of FbF for selection via aspects of survival, fecundity, and mating success were significantly different: on average, selection on mating success was stronger than on survival. Comparisons of estimated linear selection gradients and differentials suggest that indirect components of phenotypic selection were usually modest relative to direct components. The absolute values of quadratic selection gradients FgF were exponentially distributed with an overall median of only 0.10, suggesting that quadratic selection is typically quite weak. The distribution of g values was symmetric about 0, providing no evidence that stabilizing selection is stronger or more common than disruptive selection in nature.

And PZ Myers rebuttal to Berlinski’s ‘arguments’ can be found here:

Has Dembski even read the paper in question I wonder? What about the quote from the paper? In context it says

“This review demonstrates that our information about the strength of phenotypic selection in natural populations has increased dramatically in the past 2 decades, but many important issues about selection remain unresolved. Our analyses suggest some specific directions for future study.
First, higher methodological standards are needed for future studies of selection (Gurevitch and Hedges 1999; Fairbairn and Reeve 2001). Most studies to date are unreplicated and have sample sizes too small to detect selection of typical magnitude. To reduce problems with Type I errors, significance testing of selection gradients and differentials should adjust for multiple tests within studies. Future studies should also report phenotypic variances and covariances among traits and standard errors on selection differentials so that appropriate meta-analyses can be conducted.
Second, we have abundant information about directional selection on morphological traits. By contrast, selection on quantitative behavioral and physiological traits remains largely unknown and should be the focus of future studies.

Comment by WedgieWorld — April 27, 2005 @ 8:30 pm

Read more!