Re: Evolution appears fulfilled

Adam Crowl (qraal@hotmail.com)
Wed, 23 Dec 1998 04:48:59 PST

>Date: Tue, 15 Dec 1998 15:50:59 -0800
>To: asa@calvin.edu
>From: "Arthur V. Chadwick" <chadwicka@swau.edu>
>Subject: Re: Evolution appears fulfilled
>
>At 04:34 PM 12/15/98 -0400, David wrote:
>

>One of the evolutionary scientists' biggest assumptions is that the
>molecular clock is reliable.... When Levinton gave his paper [at the
1996
>GSA meetings in New Orleans] he stated that the molecular clock can be
best
>compared to a sun dial in the shade, which isnít very encouraging for
his
>method, but he and his colleagues still believed that it yielded data
>sufficient to test the theory of the rapid evolution of life at the
base of
>the Cambrian....
>
>From their molecular clock data they concluded that the initial
divergence
>of metazoan life forms occurred about 1.2 billion years ago (+/- 50 to
250
>million years) . The base of the Cambrian is currently dated at about
543
>million years ago , so their conclusions require a half billion years
of
>metazoan history before the Cambrian.
>
>The proposal that complex
>metazoan animals, ancestral to such things as molluscs, trilobites,
>vertebrates, sea urchins, corals, and many others, existed for a half
>billion years before the Cambrian implies that they lived all that time
>without leaving a fossil record. This pretty much requires that before
the
>Cambrian they existed as soft worm- or larvae-like forms, with the
general
>genetic make-up of the Cambrian groups but without their skeletonized
>morphology.
>
>Now the questions. The first of the two questions was - why are trace
>fossils (fossil tracks, trails, and burrows) so rare before the base of
the
>Cambrian, if these animals existed for that half billion years?

You've already mentioned one possibility Art. Too small. If they existed
as sexually mature embryo-like forms then they aren't likely to leave
trace fossils. There's room to move in such molecular studies though and
error factors that can significantly alter the outcomes. Certain coding
areas are more conserved than others and other effects can come into
play that skew the rate of mutation away from the "random" rate that a
true clock requires. More recent studies bring the ages down to ~ 670
mya. And new fossils are being found of phosphatised embryoes in the
apparent "blank" period of ~ 670 - 540 mya. In other words more data is
arriving as we speak.

> An
>internationally recognized expert on trace fossils stood up, presumably
to
>answer the question. However, he talked about other things and the very
>important question never was answered. At the end of the discussion
another
>scientist stood up and commented on the implication that all the
>skeletonized phyla developed skeletons at about the same time in the
>Cambrian. He asked - why are all these types of animals living for so
long
>and then all making skeletons all at once? He then asked, with some
vigor -
>'Why are you avoiding the real question?' After a pause, one member of
the
>original presenters answered 'because itís really hard (a hard
question)'.

It is. But does it have to be made harder by jumping on new data too
quickly? Take the recent trace fossils that could be 1.1 giga years old.
Questions have been asked about interpretation [are they from animals?]
and the rock unit's dating [it could be just 570 mega years old.] Does
this say that the whole field is a hopeless muddle? No. But it does say
that we need patience before making absolute pronouncements.

>He went on to say that they hoped answers would come from further study
of
>developmental biology.
>These two questions were apparently not asked by people who doubted the
>evolution theory, but by evolutionary scientists willing to ask the
hard
>questions that need to be addressed as they try to test between
different
>hypotheses. The fact remains that the Cambrian explosion is one of the
big
>challenges to naturalistic theories that still remains unanswered.
>
Unanswered? Many answers have appeared. They're all badly in need of
more data and more experimental design to discern what might be true to
the data as it is. Conway Morris' "Crucible of Creation" really opened
my eyes to some of the more "naturalistic" solutions to the puzzle, and
he's a Believer. Do we have to insist on a misleading dichotomy of
"explanations" - God or [unjustified] evolutionary speculation? I don't
think the speculation is all that unjustified. And I don't think that
God is just present at the fringes of our knowledge and our world.

Adam

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