It's so good to have Paul Nelson keeping an eye on us. I'd begun to think
that he wasn't interested in our discussion anymore :-)
Two comments:
1. The conservative nature of these regulatory genes is not a serious
problem in my view. Subtle differences in target sequences and the
cascading out of the effect of the conserved regulators can produce by the
end of ontogeny rather different final forms.
2. Let's remember that morphology and ontogeny are not exclusively
genetically directed: notions of law-bound form in biological structures
and self-organization are on the comeback in biology and they provide clues
to some of the answers to these unsolved problems. To use chaos/complexity
ideas: very small changes can result in biological structures settling in
a novel attractor that morphologically is very different. I'll point again
to Kauffman and Goodwin (see the bibliography from Brian Harper).
It's likely that you can replace nearly every chimp gene (including most of
the homeotic genes) with human sequences and still get a chimp. There are
probably only a handful of genes that differ by only a small amount; but
those differences are sufficent to switch ontogeny of key distinctly human
features.
I'm with Paul however in that I can't spend too much time in this
discussion. I do have a real job, 5 kids, and a wife.
TG
Paul, maybe I'll see you in January.
_____________________________________________________________
Terry M. Gray, Ph.D. Department of Chemistry and Biochemistry
Calvin College 3201 Burton SE Grand Rapids, MI 40546
Office: (616) 957-7187 FAX: (616) 957-6501
Email: grayt@calvin.edu http://www.calvin.edu/~grayt