From: Keith Henson (email@example.com)
Date: Wed 11 Jun 2003 - 05:25:47 GMT
At 12:32 AM 11/06/03 -0400, Scott wrote:
>Aren't flies and humans segmented (though not as obvious in post-embryonic
>humans with skin covering) pointing to early acting and homologous
>developmental processes and a phylogenetically early common ancestor? I
>vaguely recall a term for a hypothetical common ancestor called
>*Urbilateria*. Google that one for kicks.
Thanks. I was looking for this:
(in the context of eyes which apparently evolved before the common ancestor.
But it obviously doesn't happen that
often, and I ask him where his passion for
taxonomy and evolution came from. It
began, really, in 1994, he says. He
published a scientific correspondence in
Nature providing new evidence to shore
up an old idea, one that had surfaced in
the nineteenth century. Observations of
the bodies of many different species
suggested that at some point in evolution,
torsos had gotten turned around, that
insects' bellies became vertebrates' backs.
This could finally be substantiated
through genetic evidence, he discovered.
The genes that form the front of a wide
range of species are related to those that
form the backs of others, and vice versa.
"From then on I was hooked," he says.
Right on the segments business, and vertebrate ribs correspond to insect
legs in the Hox genes that code for them. Because the genes that set up
the gradients are on a row down the chromosome, swapping them around (which
is known to happen) will reverse the front to back gradients.
>You'll get nowhere with Dace on this one so don't sweat it. You've done a
>great job of countering his rhetoric. Psi phenomena have no place in
>developmental biology. Whatever use morphogenetic fields have as a
>concept, they are probably best considered as placing genes in a
The "fields" people could locate in the old cut and paste experiments are
clearly chemical gradients, signals, that turn on/off genes.
> and as a way of getting away from simplistic reductionism (perhaps even
> as far as putting the "selfish" evolutionary gene of Dawkins and Williams
> in its place, taking some wind out of its rhetorical sails).
I really don't see genetics as simplistic, reductionism or not. Nor do I
see "selfish" as more than a shorthand to keep from having to go through
the causal chain of evolution over time every time you want to talk about
genes. Dawkins spent much time in Selfish Gene on a rowing crew
(cooperative) metaphor. In humans there are at least 30,000 genes. I can't see the interaction of human genes as being a whole lot less complicated than the interactions of 30,000 people.
>One of the best modern treatments of the field concept is a 1996 article
>by Scott Gilbert (a developmental biologist with his own textbook), John
>Opitz, and Rudolph Raff (a developmental biologist with a book that
>attempts to popularize evolutionary developmental biology called _The
>Shape of Life_) called "Resynthesizing evolutionary and developmental
>biology" appearing in the journal _Developmental Biology_ (173): 357-72.
I followed this when it was being reported in Science and Nature so I am
fairly well up on it.
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