Re: Cambrian explosion bit of an embarassment



"On 10 Sep 2006 05:40:32 -0700, in article
<1157892032.388383.37920@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, Ron O stated..."


topmind wrote:
You have to admit that the Cambrian Explosion is a bit of an
embarassment from an evidence standpoint. Out of a period of no more
than about 5-10 million years, these features "popped" out of nowhere
in the fossil record:

* Movable and jointed limbs
* Mouths
* Eyes
* Digestive tracks
* Body armor
* Nervious system

(I am not aware of any strong pre-Cambrain evidence for these, but may
have missed some.)

The precambrian animals, if it is even safe to call them that, are
almost mushroom-like as far as anatomy. They went from oblong blobs to
the familar body plans still around today in a relative blink of an
eye. The pre-cambrian critters are almost not even tracable to the
cambrian ones.

I am not questioning evolution in general here, but the CE is just
fricken odd and has got to be a hard-sell to skeptics. The huge jump in
complexity is simply missing from the record. It is analogous to going
from mechanical relay computers to silicone chips in 3 months without
any record of that 3 months. We have:

* Sudden increase in complexy (see list above)
* Lack of tracability to pre-cambrian forms
* No clear record of the transitional forms (list of features above
appeared at the same time)
* All of the above happened to all animals, not just some

It has got to rank as one of the greatest scientific mysteries, perhaps
rivaling dark matter.

-T-

Molecular evidence indicates that various lineages existed for possibly
hundreds of millions of years before the Cambrian explosion. Soft
bodies do not preserve well. That is a simple fact. Just look at
nematodes. This is one of the oldest lineages of worm like of
metazoans and there are an estimated half a million extant species of
them, but they have such a poor fossil record that you can probably
count the number of fossils on the fingers of one hand. None of them
from Cambrian or Pre Cambrian deposits, but they predate things like
mollusks and arthropods by a considerable amount of time.

When we get lucky enough to find nematode fossils we will likely begin
to find the other worm like ancestors to the Cambrian fauna. If you
don't like that explanation, explain the molecular evidence and the
fossil worm tracks that we do find in Pre Cambrian rock. We can't tell
what type of worms left those tracks, but something did, and we have
other evidence that there were multiple lineages of metazoans evolving
at that time.

The metazoan common ancestor goes back quite a ways. We can trace it
at the molecular level to a specific lineage of sponges. If you don't
know what that means, it means that there are extant sponges that are
less closely related to other sponge lineages than they are to us. Not
having all the answers doesn't mean that you don't have any.

A couple of comments.

As you point out, the evidence for evolution is *not* exclusively a
matter of fossils. If there were no fossils at all, evolution would
still have been the best explanation for features of life like the
complex nested hierarchy of life, the complexities of the
distributions of living forms over the earth (biogeography), and
several other lines of inference. Fossils are nice, and they agree
with all of the other evidence, but they aren't everything.

And it is worth pointing out that every active field of inquiry has
its puzzles. If there weren't any puzzles, then people would have
all the answers, and few scientists would be studying it.
The fact that there are some puzzles at the extremes of
evolutionary biology just makes evolutionary biology like every
other science. It's like disputes about human evolution -
whether it's "Out Of Africa" or "Multiregionalism" - the questions
are not about whether Homo sapiens evolved, but just about
details.

It seems to me that there is a kind of tacit admission, whenever
some of the extremes are brought up, that the rest of the field
is pretty well established. When people bring up the Cambrian
Explosion, are they telling us that there isn't anything
significant to dispute about the last 500 million years?


--
---Tom S. <http://talkreason.org/articles/chickegg.cfm>
"... have a clear idea of what you should expect if your hypothesis is correct,
and what you should observe if your hypothesis is wrong ... If you cannot do
this, then this is an indicator that your hypothesis may be too vague."
RV Clarke & JE Eck: Crime Analysis for Problem Solvers - step 20

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