Choosey Peahens Choose Evolution

By Dave Wisker, Graduate Student in Molecular Ecology at the University of Central Missouri.

Creationists The Discovery Institute must have drooled when they heard a paper had been published by the respected journal, Animal Behaviour, which apparently reported that peahens did not prefer peacocks with more elaborate trains. Takahashi et al. (2008) appears to contradict several well-known studies that reported the opposite, and which have been cited as evidence for sexual selection in peafowl. Since the peacock’s tail is a venerable symbol of runaway selection for a secondary sexual trait, the DI ARN jumped on the story, crowing, with breathless excitement:

The alleged amazing powers of natural selection are much diminished as a result of these findings. The argument that it is “powerful enough” to maintain the feather display against the negative effects of attracting predators must be dropped. Furthermore, it appears not powerful enough to remove the display when it becomes an “obsolete signal”. Darwinists need to think very hard about the way they do science. This is a clear example of how a Darwinian hypothesis has become accepted as scientific fact, yet now has been disproved by some rigorous empirical research. This is a falsified prediction. This means that numerous textbooks and web sites need to be revised. More importantly, Darwinists should cease giving the impression that they have the keys to understand the natural world. So much of this ‘understanding’ is like peacock feathers - lots of show and no substance. Richard Dawkins extols Darwinism as a beautiful theory, but whenever we look closely, it fails to account for the observed data.

Unfortunately for the DI ARN, their enthusiasm for this paper may be premature, as I noted in a guest entry on Denis Ford’s “This Week in Evolution”. Essentially, the paper has two major problems (my article deals with some other minor ones as well):

  1. The authors used a different methodology to determine male reproductive success than the other studies, which makes comparing them very difficult. While the British and French studies measured male reproductive success by observed successful copulations, the Japanese one estimated the number of successful copulations, based on female pre-copulatory behavior.
  2. The genetic variance in tail morphology in all of the studies was very low (Takahashi et al.’s study had the lowest), which only magnifies the differences in methodology. Small differences in number of successful copulations have greater weight because the very low variation makes determining any kind of selection very difficult.

The main thrust of my article is that the differences in methodology for determining male reproductive success were magnified by the very low variance in the trait, invalidating comparison between the studies. It should be noted that Marion Petrie and Adriane Loyau, primary authors of two of the three major studies confirming peahen’s preference for more elaborate male trains, are in the process of publishing a reply to Takahashi et al’s paper. One wonders if the DI ARN will mention that.