8. Why sexual selection?
According to PBS, the male peacock's beautifully-colored tail is easily explained using sexual selection: females prefer the colorful "eyes" on the tails of males. Has the evolutionary origin of the peacock's tail been explained?Sexual selection merely pushes the question back: why should female peacocks prefer male peacocks with tails that have "eyes"? Absent a linkage to survival and reproduction, sexual selection is now a circular argument: male peacocks have beautiful tails because females prefer such tails, and females prefer such tails because they are, well, beautiful. Under sexual selection, explanations become arbitrary because traits are preferred simply because a biologist deems them "attractive." But sexual selection rarely provides an external adaptive reason to explain why such traits should be "beautiful" to the opposite sex.
Despite its ability to arbitrarily select for virtually any trait wished for, sexual selection has been invoked to account for the evolutionary origin of humanity's most cherished abilities, including art, literature, music, mathematics, religious belief, and even scientific genius. Once you define something as "beautiful" or "attractive," the magic wand of sexual selection can produce virtually anything an evolutionary biologist wants.
But there is a more fundamental problem here: the existence of sexual selection itself begs the very question, why are there male and female peacocks at all?, i.e. why did sexual reproduction evolve in the first place? Sexual organisms only pass on 50% of their genes to offspring, whereas asexual organisms make clones that contain 100% of the parent's DNA. Thus organisms that hypothetically evolved sexual selection suddenly experienced a 50% drop in fitness. The fitness cost of sexual reproduction is further explained in the critical response to the PBS Evolution series, Getting the Facts Straight:
Reference Cited:
1. Getting the Facts Straight: A Viewer's Guide to PBS's Evolution, page 73 (Discovery Institute Press, 2001), at http://www.reviewevolution.com/viewersGuide/viewersGuide.pdf.
