On Sun, 11 Jun 1995 13:16:56 -0500 (CDT) you wrote:
JM>In a recent post, ( Sat, 10 Jun 95 09:34:01 EDT - topic
>Re: Gradual Morphological Change) Stephen Jones said in response
SJ>to something that Glen said: "Yes. If Glenn's models were true,
>we would expect to see continuing "Cambrian Explosions". Why was
>there only one?"
JM>Although the Cambrian explosion was a dramatic one and one
>that does not fit well with a gradualistic model
Indeed it blows it completely out of the water! <g> Gould says:
"Three billion years of unicellularity, followed by five million years
of intense creativity and then capped by more than 500 million years
of variation on set anatomical themes can scarcely be read as a
predictable, inexorable or continuous trend toward progress or
increasing complexity."
(Gould S.J., "The Evolution of Life on the Earth",
Scientific American, October 1994, p67).
JM>it is not true that there were not other sudden increases in Taxa
>at various times in the fossil record.
I did not claim that there were not other sudden increases in taxa at
other times. Indeed, the Progressive Creation model would predict
it. But these later "explosions" involved already existing body plans.
JM>I might also add that most of the
>chaps studying the fossils of the Cambrian would say it is less
>dramatic than was previously thought.
Well Gould must be sadly out of touch then, because as late as
October 1994 he wrote:
"The Cambrian then began with an assemblage of bits and pieces,
frustratingly difficult to interpret, called the "small shelly fauna."
The subsequent main pulse, starting about 530 million years ago,
constitutes the famous Cambrian explosion, during which all but one
modem phylum of animal life made a first appearance in the fossil
record. (Geologists had previously allowed up to 40 million years for
this event, but an elegant study, published in 1993, clearly restricts
this period of phyletic flowering to a mere five million years.)..
Although interesting and portentous events have occurred since, from
the flowering of dinosaurs to the origin of human consciousness, we do
not exaggerate greatly in stating that the subsequent history of
animal life amounts to little more than variations on anatomical
themes established during the Cambrian explosion within five million
years.
..even the most cautious opinion holds that 500 million subsequent
years of opportunity have not expanded the Cambrian range, achieved in
just five million years. The Cambrian explosion was the most
remarkable and puzzling event in the history of life.
(Gould S.J., "The Evolution of Life on the Earth",
Scientific American, October 1994, p67).
JM>This does still not mean that the Cambrian with its quite
>abrupt appearance of hardshelled organisms is not unique in the
>largeness of the scale. I just wanted to correct the impression
>that Steve's post may have left that this was the only dramatic
>appearance in the fossil record.
Thanks for the info James, but it does not really address the main
point. Gould says "The Cambrian explosion was the most remarkable and
puzzling event in the history of life" and that "the subsequent
history of animal life amounts to little more than variations on
anatomical themes established during the Cambrian explosion within
five million years". If Glenn's models were true, we would expect to
see regular continuing "Cambrian Explosions", on the same scale as the
original, with genuinely new body plans.
Stephen