"It is clear from the fossil record that chordates and arthropods diverged at least by the Cambrian. The appendages of these two groups are not homologous because phylogenetically intermediate taxa (particularly basal chordates) do not possess comparable structures. The most surprising discovery of recent molecular studies, however is that much of the genetic machinery that pattern the appendages of arthropods, vertebrates and other phyla is similar." (Shubin et al. (1997) "Fossils, genes and the evolution of animal limbs", Nature 388)Is this true? And if so, why doesn't it matter (as I'm sure that there is an excellent darwinian explanation for it)?
There is, therefore, confusion as to what the genetic basis is for homologies. Clearly some homologies seem to share similar genes (upholding Darwinism) but many do not. Also, in the case of limbs, as already mentioned, the same sort of genes seem to control the limb development of widely separated taxa such as arthropods and vertebrates. It is a puzzle as to how such widely separated and phylogenetically distinct phyla could have the same genes for such totally different limb designs.
Antony Latham, "The Naked Emperor", 176-7
Friday, January 05, 2007
Labels: Evolutionary theory