>At 08:47 PM 2/17/99 +1000, Adam wrote in response to Karen:
>>>I read about finds of centepedes, arachnids, and insect remains preserved
>>>in exquisite detail in Devonian rock form upstate New York, "similar to
>>>modern forms" (Science News 123:356-357, June 4, 1983) -- have these been
>>>found to be contamination?
>>Probably not. They are rather conservative groups with little pressure to
>>change grossly beyond their standard forms, so similar is no surprise at
>Adam, you must know this terminology (..rather conservative... ...little
>pressure...) is standard ( and meaningless) description of what is observed
>as if it had explanatory value. Please explain why you think this group is
>"conservative" (and don't tell me its because they are the same today as in
>the Devonian), and why you think there is "little pressure" on them.
The pros have already answered your questions, but I thought I had better
make it personal. "Conservative" is basically an empirical observation -
those groups speciate through-out time, but their "bauplan" remains much the
same - so I have to tell you that they are "similar", but not the same. As
for "little pressure" you're right - not a thought out response. Those
groups change all the time, but they haven't changed into anything "new".
Why? I don't know, but their basic designs are successful [empirical
observation] and it seems that they're "stuck in" those basic forms. I can't
imagine what pressure would cause them change - but if "pressure to change"
is real then it must be small for those groups. Perhaps macro-mutational
jumps are needed to take a group, like spiders or vertebrates, off their
adaptive peaks and into the "wilderness of form". And successful jumps are
now unlikely once the moulds are cast and refined over mega-years. It's a
very under-explored territory: the question of why these forms and not some
other. I can see connections between them all sufficient to convince me of
common ancestry [tho maybe not you] but why a certain bauplan remains so
stable is a deeper question than I can answer. We need more evidence and
My post was really in response to the usual Creationist rhetorical ploy of
implying that conservation of form across mega-years is somehow at odds with
evolution. No Darwinist believes it is and I don't see it is so either. Life
has changed and has remained the "same" - that's fact. Why? Internal
constraints? Physical constraints? Divine dictates? All of these? What do
you think, Art?
PS You strike me as being a "critical Creationist" rather than the sort who
leaps on any scrap that might mean something, like so many others. We
evolutionists need sceptics like you to keep us honest - thanks.