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The evo-devo approach advocated in the McNamara and Long book is in my
opinion one of the most exciting advances in evolutionary biology. Rudi
Raff's book "The shape of life" is a great read, although 4 years after
its publication it is already somewhat outdated (especially the
invertebrate phylogeny, which predates the tripartite bilaterian tree).
I have two comments with respect to the quoted passage from "The
1. Many of the molecular biologists in this area have been very naughty
with their use of the word homology. Here's an example from a
recent paper by Jason Hodin (J. Exp. Zool. (Mol. Dev. Evol.) 288: 1-20
2000) which discusses the role of the gene Pax6 in regulating eye
development in both the mouse and Drosophila:
"This example really brings into focus the problems encountered with
the use of the word "homology" to describe both molecules and
morphology. Yes, the "homologous gene" (properly, the "orthologous
gene") is used to build both the fly and mouse eye. But are they used
in the same way? The appropriate way to address this question is not to
see if the mouse gene works in fly eye development. The mouse gene was
found to regulate eye development in Drosophila (Halder et al. 1995),
yet there is a functional Pax6 in C. elegans [a nematode], an organism
that lacks eyes altogether. Based on its sequence similarity, I wager
that C. elegans Pax6 would also work in fly eyes. A positive result
tells you only that the biochemical properties of the protein have been
conserved, not necessarily that its function within a certain
morphological structure has also been conserved."
Returning to the insect wings example, one could say that the
regulatory genes are orthologous (homologous), but whether the
resulting morphological structures are homologous is another matter.
Incidentally, the link between crustaceans and insects may be closer
than Averof and Cohen imagined. Wilson et al. (Mol. Biol. Evol. 17:
863-874 2000) suggest that malacostracan crustaceans (e.g. prawns) may
be closer to insects than they are to branchiopods (brine shrimp). Thus
crustaceans may be paraphyletic, and insects are actually derived
2. Evo-devo approaches can be used to test hypotheses on dinosaurs.
Examples include Steve Gatesy's work on avian vs non-avian theropod
locomotion, and Richard Prum's work on feather evolution. I think this
sort of reasoning has the potential to be far more productive and
meaningful than what often passes for scientific discourse on this list.
Kendall Clements firstname.lastname@example.org