Re: Evolution appears fulfilled

Arthur V. Chadwick (chadwicka@swau.edu)
Tue, 15 Dec 1998 15:50:59 -0800

At 04:34 PM 12/15/98 -0400, David wrote:

>Very rapid evolution is another naturalistic scenario that is possible.
>However, the current rate of discovery of new kinds of Precambrian fossils
>is very high, and I do not think we can rule out new discoveries as people
>take another look at older Precambrian deposits. We still do not really
>know what to expect a proto-metazoan to look like, how big it should be,
>etc.
>
>Also in this context, it should be noted that most people who try to do
>molecular clock estimates of the time of metazoan origins do not seem to
>understand the fossil record or statistics.

You are gunning down some big names in evolutionary biology with that
comment. But, oh, well, thats nothing new to me!

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....

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. They also concluded that the
beginning of Metazoan phyla was not an explosion, but was somewhat spread
out during that half billion years.

A couple of days later these papers were discussed in a 'Hot topics
discussion' during the noon hour. Four scientists gave brief presentations
on the new ideas about the Cambrian explosion, followed by audience
questions and comments. Many questions dealt with technicalities of their
research method, but two questions stand out. A little background is
necessary before dealing with these questions. 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? 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)'.
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.

Art
http://biology.swau.edu