Explanations for the Cambrian Explosion

Activity at EvC has been rather low recently. Perhaps it's because we're all talking about obscure and highly technical stuff that bores the average person. It might be nice to talk about one of the classics again.

I haven’t seen a thread devoted entirely to the Cambrian Explosion for awhile, even though the topic has come up often in passing in many different threads. I particularly like the Cambrian Explosion, because, as an entomologist and a long-time science-fiction fan, I have always been interested in bizarre creatures, and the Cambrian Explosion has its share of bizarre creatures, such as Opabinia regalis (my personal favorite).

So, what does everyone think about the Cambrian Explosion?

As most of us know, creationists will often cite the apparently rapid radiation of animal groups around the beginning of the Cambrian period as evidence against the uniformitarian principles that scientists generally consider prevalent in the processes of evolution. Often, however, reference to the Cambrian Explosion is only made in passing, and no major attempt is made to explain its relevance in the thread. So, I propose this thread to discuss the role of the Cambrian Explosion in the evolutionary and ID models of natural history.

I argue that the Cambrian Explosion does not evidence a special creation. I would like to explore perhaps three main themes:

1. The Phyla Argument: Creationist claims inflate the drama of the event by pointing out that all modern phyla appear within 50 million years, while failing to note that the difference between phyla at the time was far less than the difference between their descendants today. This was discussed rather thoroughly here, so it need not be emphasized in this thread: I included it so that it wouldn’t be simply overlooked.

2. The Pace Argument: Creationists claim that the “rapid” appearance of a diverse fauna must be interpreted by evolutionists as an unrealistically fast rate of change, and that it is thus better explained as an untransitioned, spontaneous creation. However, I contend that mutations need not have happened at a higher rate than today, because the lower diversity in the fauna would have lowered competition and allowed a greater proportion of the mutations that occurred to survive and accumulate. Aside from this, there may not be any support for the claim evolution during the Cambrian Explosion happened at a faster pace, anyway.

3. The Snapshot Effect: Creationist claims of suddenness for the Cambrian Explosion are also compounded by the “snapshot” effect. Claiming that the appearance of Cambrian shelly fauna in only a handful of locations is evidence of spontaneous creation is akin to claiming that the discovery of only a single praying mantis in a field indicates that said mantis must have been created by God, because there was nothing around it for it to have evolved from.

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I would be interested in hearing creationists' response to the last two points (let's save point #1 for emergencies, such as if the thread dies down too early, or something).

Edited by Adminnemooseus, : Fix URL - There was a space bunging it up.

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-Bluejay

Darwin loves you.

Thread moved here from the Proposed New Topics forum.

One point that creationists, either knowingly or unknowingly, grt the impression that all thye phyla formed during the Cambrian explosion. Most of the current phyla existed before the Cambrian.
Citing Dawkin's The Ancestor's tale,Chap 26

IN THE DEEPS of geological time, and iof the hard support of fossils, we are now entirely reliant on the technique that I referred to in the General Prologue as molecular range finding. The upside is that the technique is getting even more sophisticated. Molecular range finding confirms a belief longheld by comparative anatomists, or more strictly comparative embryologists, that the greater part of the animal kingdomis divided into two great sub-kingdoms, the Deuterostomia & the Protostomia.

from this chapter it shows that the separation of these 2 sub-kingdoms occurred before the Cambrian. with most of the phyla from at least the protostomes having evolved before the Cambrian.

the prtostome phyla before the Cambrian:

Chaetognatha - Arrow worms
Tardigrata - Water Bears
Onychophora - Velvet Worms
Arthopoda - Insects, crustaceans, arachnids etc.
Cephalorhynchs - no common name
Nematoda - Round worms
Nenatophora - Hairworms
Gnathifera - Rotifers
Platyhelminthes - Flat Worms
Brachiozoa - Brachiopods (lamp shells)
Entoprocta - Goblet Worms
Bryozoa - Moss Animals
Nemertea - Ribbon Worms
Mollusca - Clams, squid, octopi etc.
Annelida - Segmented worms
Sipunculoidea - Peanut worms

All of these phhla existed before the so called Cambrian Explosion.

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There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

There are a couple of "explanations" for the Cambrian explosion.

First, this so-called "explosion" took place over several tens of millions of years -- hardly instantaneous, and certainly not consistent with the Genesis account.

Second, as you point out, there is a much longer fossil record that extends much, much farther back before the Cambrian. Also, the current genetic evidence indicates that the splitting of the major phyla occurred well before the Cambrian.

Finally, there is not a single example of an indisputably modern life-form that is found from the time of the Cambrian explosion. Even those species that can be identified with extant taxa are very different from the modern forms.

In short, there is nothing to explain. In fact, it is the YEC who has to explain why, if this is supposed to be a record of the Genesis event, why there are no modern life forms, why life forms are dated much earlier than the Cambrian, and why the Cambrian Explosion is dated to a very wide range of time -- the same explanations that the YEC has failed to provide to geology in general.

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Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev

quote:

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Chaetognatha - Arrow worms
Tardigrata - Water Bears
Onychophora - Velvet Worms
Arthopoda - Insects, crustaceans, arachnids etc.
Cephalorhynchs - no common name
Nematoda - Round worms
Nenatophora - Hairworms
Gnathifera - Rotifers
Platyhelminthes - Flat Worms
Brachiozoa - Brachiopods (lamp shells)
Entoprocta - Goblet Worms
Bryozoa - Moss Animals
Nemertea - Ribbon Worms
Mollusca - Clams, squid, octopi etc.
Annelida - Segmented worms
Sipunculoidea - Peanut worms

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Most of those are not Phyla.

Bluescat,

You sure about that? Based on what data? Bryozoans don't turn up in the fossil record until the ordovician, the period after the cambrian.

Mark

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There are 10 kinds of people in this world; those that understand binary, & those that don't

Then what are they? Most were Phyla even when I was in school back in the 50's & 60's. Some have different names, They are listed as phylea in the source I listed The Ancestor's Tale.

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There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

No, you're right. I was getting confused. Sorry.

From a combination of Fossil record, DNA sequencing and a process Dawkins calls Triangulation, which combines the fossil record with the similarity of the DNA sequencing and relates to when the similar sequencing appears in a common ancestor in what he calls the Molecular Clock. Do to the misconception that many people have that the so living fossils have not changed since the whatever era, what is considered the time a particular phylum occured in the geological time line is not necessarily correct. The common ancestor of both the Bryozoa & the Entoprocta is also the common ancestor of the Brachiozoa, Nemertea, Mollusca, Annelida & Sipunculoidea, which broke away from the protostome main line some time prior to the Cambrian.

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There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

bluescat48 writes: The common ancestor of both the Bryozoa & the Entoprocta is also the common ancestor...

I must confess I'm not a scientist--nor do I know much about this stuff. But, I, as a plain layman, can't understand scientists concluding about a "common ancestor".

They discover common parts of certain animals or what not and they say "common anscestor". I can't be convinced by that. To my mind, there are other valid conclusions about this "common parts" (Homologous, is that correct?:
1) why not common ancestorS as in PLURAL?
2) why not common parts as evidence of a common designer--e.g. a Civic having common parts as Accord is evidence of common designer, HOnda? ( Of course, the draw back is the identity of the designer again... and that is admitted. But, why not designed by an unknown designer? )

3) Why not just Stop this conclusion: 'in our investigation of the fossil we found animals, plants, etc of having ALMOST similar parts?'

I have done a little bit of research on the so called "phylogenitic tree", and I am not convinced of the conclusion reached--common ancestor. All I can see are common parts. Are there not big gaps in this so called theory about "common ancestor"?

Edited by Doubting Too, : No reason given.

The term common ancestor simply means that if one traces the genetic development back to a point where the branch goes in 2 directions, the point where the branch forks is the common ancestor of the 2 branches, which is why it is singular.

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There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

choptera writes: Finally, there is not a single example of an indisputably modern life-form that is found from the time of the Cambrian explosion. Even those species that can be identified with extant taxa are very different from the modern forms.

A reference material, A View of Life, says: "Beginning at the base of the Cambrian period and extending for about 10 million years, all the major groups of skeletonized invertebrates made their first appearance in the most spectacular rise in diversity ever recorded in our planet." I understand that in that period, snails, sponges, starfish, tribolites (lobster like animals) and many other complex sea creatures appeared. Interestingly, the same book observes: "some extinct tribolites, in fact, developed more complex and efficient eyes than any living anrthoropod posseses"

How old is your reference source, A View of Life?

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There is no better love between 2 people than mutual respect for each other WT Young, 2002

Who gave anyone the authority to call me an authority on anything. WT Young, 1969

Doubting Too writes: 1) why not common ancestorS as in PLURAL?

In an evolutionary context, an ancestor is quite literally a genetically related individual. So you should not think of ancestors as merely a group of forebears, in the sense of "the people who went before us", related or not.

If you trace your ancestry and that of your third cousin twice removed, you will normally find that the both of you share two common ancestors: your great great grandfather and his wife, your great great grandmother. Your third cousin twice removed will call them great great great great grandfather and ditto grandmother - she is twice removed, hence the two extra greats. However, it could be that your great granduncle - your third cousin twice removed's great great great grandfather, but no direct ancestor of yours - is the son of your great great grandfather and his second wife. In that case you share literally only one common ancestor with your third cousin twice removed.

In asexually reproducing species an organism always has one parent, one grandparent, one great grandparent, and so on. In sexually reproducing species, it is by no means guaranteed that an individual always mates with the same partner. So, although there is the possibility that two distantly related organisms share two common ancestors, it is more practical to consider just one. So, you can literally speak of just one individual common ancestor you share with the orangutan you stare in the face in the zoo. This common ancestor lived millions of years ago and was neither a human, nor an orangutan. Much much longer ago, there lived another individual animal who was the common ancestor between you and your dog. Again, this ancestor was neither a human nor a dog. The more different the two organisms under consideration are, the further back in time their common ancestor will have lived, and the less it will have looked like either of them. But every time you consider such a common ancestor, you should be aware of the fact that it must be, of necessity, literally one individual (or at most two).

2) why not common parts as evidence of a common designer--e.g. a Civic having common parts as Accord is evidence of common designer, HOnda? ( Of course, the draw back is the identity of the designer again... and that is admitted. But, why not designed by an unknown designer? )

The phylogenetic tree is by no means the only evidence we have for the theory of evolution. All kinds of other evidence point to evolution instead of design. Besides, even the phylogenetic tree in itself is poor evidence for design. In design, if a feature does not meet requirements, it is customary to make a significant change instead of an ever so gradual movement in a certain direction. Also, we would not expect obvious mistakes, like the blind spot in the human eye, or the problematic use in bipeds of a backbone "designed" for quadrupeds, to be left untouched by a designer.

3) Why not just Stop this conclusion: 'in our investigation of the fossil we found animals, plants, etc of having ALMOST similar parts?'

That is not a conclusion, it's just a starting point of some very interesting scientific research. If you want to stop there, why would you even want to begin to investigate in the first place?

I have done a little bit of research on the so called "phylogenitic tree", and I am not convinced of the conclusion reached--common ancestor. All I can see are common parts. Are there not big gaps in this so called theory about "common ancestor"?

If a Caucasian woman gives birth to a child with dark skin and black curly hair, I don't suppose her Caucasian husband is going to say "Well, all I can see are common parts between my child and African people. There's no reason to suspect that my wife has been unfaithful." Would you?

Animal and plant breeding rely on the principle of common ancestry. If you think there was nothing to it, how do you suppose to explain its success?

There will always be gaps in human knowledge, but they are getting smaller and smaller. As far as the theory of evolution is concerned, lots of corroborative evidence is available from many different disciplines. The great thing about these different lines of evidence is that they all fit with the theory, they all point to the same conclusion: evolution by random mutation and natural selection is what really happened.

Edited by Parasomnium, : No reason given.

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"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.

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A View of Life is good, I've just finished reading it myself, but it has two problems as a reference: firstly, it's somewhat outdated ('81, if you have the same edition as me) - many of the discoveries regarding this area are more recent. Secondly, Gould considerably overstates his case regarding Punctuated Equilibrium a notion into which the sudden appearance of life in the Cambrian fits nicely. Finally, the appearance of skeletons occurs more dramatically than the appearance of phyla - probably because of a shift in the pH of the oceans.