In article <7ei8ah$1vc$1 at denws02.mw.mediaone.net>,
"Richard Norman" <rsnorman at mw.mediaone.net> wrote:
> F. Frank LeFever wrote in message
> <7eh4d6$pdc at dfw-ixnews4.ix.netcom.com>...
> >re vertebrate and arthopod inversion: yes, we (speaking for myself,
> >anyway, as a vertebrate) have skeletons on the inside, and "they"
> >skeletons on the outside; but do you have in mind something more
> >profound than that?
> >And yes, there do seem to be common mechanisms involved in brain
> >plasticity at the level of memory formation and at the level of
> >F. Frank LeFever, Ph.D.
> >New York Neuropsychology Group
>> My impression is that "vertebrate/invertebrate inversion" is
> related to the dorsal vs ventral location of the main longitudinal
> nerve cord, possibly adding the location of the heart (vertebrates
> have dorsal nervous system, ventral heart -- some invertebrates
> have the opposite). The same argument has been used to
> "explain" the decussation of vertebrate central/peripheral
> connections -- the left brain connected to the right body.
>> I think that all the developmental, molecular biological, genetic,
> and evolutionary work in the last 150 years or so argues
> against any simple "inversion" origin of the vertebrates.
Maybe vertebrates and arthropods diverged from a common ancestor and the
dorso-ventral "inversion" relates to a correspondence in some early acting
genes that are homologous between fruitflies and vertebrates and their
expression patterns are on opposite sides of the body. Plus, the CNS is
dorsal in the vertebrates and ventral in insects.
Geoffroy might have taken things a little far way back when, but there could
be a kernel of truth to the notion of inversion. IIRC Geoffroy ticked off
Cuvier for something that didn't mesh with Cuvier's embranchments. They had
some sort of debate regarding form and function, but we don't need to go
there. I need to get some more recent references than the Arendt and
Nubler-Jung stuff. Their brief mention of CREB interested me though.
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