The Cambrian Revisited

| 26 Comments

Although I hate to give credibility to statements which are so anti-science, I also believe that educating those who are willing to hear the “rest of the story” is important.

Point in case:

In a recent blog posting, Denyse O’Leary stated the following on the Cambrian explosion. Since her comments may be of direct interest to this group, I would like to repeat them here and discuss why they are flawed.

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26 Comments

Thanks for this PvM - more ammo for the arsenal against the quacks.

Great piece. One typo:

The paper above also discusses the problem of the concept of a phylum, which is highly artificial and has lead to much confusion.

I think you mean “led”, not “lead”.

Thanks PvM, PT at its best.

“creation-science and evolution are the sole scientific alternative explanations”

But then, either ID is “creation-science”, or it is unscientific, right? ;-)

I am not a biologist, but I have never had an impression that the Cambrian explosion is a slightest problem for evolution. Quite the contrary. First, you have some fossils prior to Cambrian. Then, during many milions of years, divers life forms appear. These are, at least to my untrained eye, quite different from current life, several hundred million years later. Now if that isn’t by definition evolution, then I don’t know what is.

I don’t think this basic fact was a controversy 10, 15, 20 or 50 years ago. The scientific dispute whether the Cambrian explosion is an artifact of cladistics or the fossil record, or if it really is a quicker diversification of life than usual, has nothing to do with it. This guy is either absolutely ignorant of basic facts or is lying. So I am glad you share the recent findings with us, but one should be aware that they shouldn’t be involved in any discussion with these crackpots. In my eyes it only gives a false impression that the Cambrian explosion was some kind of fundamental problem for evolution earlier.

Should we offer to pay for Denyse to do an elementary course in geology?

It was the view of the great Adam Sedgwick who first elucidated the Cambrian in Fall 1831 after his assistant Charlie went home for the shooting season and went fro a sail round the world instead, that similar types in his day”have committed the folly and the sin of dogmatizing on matters they have not personally examined.” (106) and regarded some as “beyond all hope of rational argument.”

As good creationist Sedgwick pointed out some arguments are beyond rational argument

total morphospace

Like, totally cosmic, man.

Outstanding info! I love this site.

I’ve looked at the fossil record fairly closely, and I have not seen one example of a known fossil specimen that is hugely different anatomically than every known specimen that is older than it. For instance, we don’t have a hippo specimen that is 700 million years old. Moreover, the overwhelming majority of known organisms are very similar anatomically to at least one known organism that is older than they are. For instance, I’m similar to my father. And see the sequences of specimens from apes to humans. See the sequence of specimens from reptiles to early mammals.

Of course the fossil data does not, by itself, enable us to determine that self-replicating molecules that were on earth about 3.8 billion years ago evolved (through reproduction) into all the organisms that have lived on earth. However, that one piece of data does not, by itself, enable us to determine that an event occurred does not mean that the event is no more likely than not to have occurred. For instance, our understanding of the speed that light travels does not, by itself, enable us to determine that the known universe is about 14 billion years old. But our understanding of the speed of light plus our understanding of other data does enable us to determine that the universe is about that old. So that the fossil record does not, by itself, enable us to determine that self-replicating molecules that were on earth about 3.8 billion years ago evolved (through reproduction) into all the organisms that have lived on earth does not mean that this claim is no more plausible than not.

Some of the key data in favor of the idea that self-replicating molecules that were on earth about 3.8 billion years ago evolved (through reproduction) into all the organisms that have lived on earth is that the existence of trillions and trillions of organisms has been proximately caused by sexual or asexual reproduction. That is how I got here. Second, no event other than a sexual or asexual reproduction is known to have proximately caused the existence of any organism, and none of the organisms that are alive today had their existence proximately caused by an event other than sexual or asexual reproduction. Third, when organisms reproduce asexually, the offspring often is a little different (in terms of genotype and phenotype) than its parent. For instance, when cells divide, the daughter-cell often has a different genome than its parent-cell. Fourth, in sexual reproduction, the offspring always is different (in terms of genotype and phenotype) than both of its parents. For instance, I’m different than my parents. I inherited 23 chromosomes from my mother, and 23 from my father. And none of those chromosomes ever touch each other. Fifth, the oldest known fossils are the remains of bacteria that were on earth 3.5 billion years ago. Finally, chihuahuas and saint bernards youngest common ancestor is less than 100,000 years old.

In addition, the phrase “Cambrian explosion” is misleading. It suggests that some known specimens that are about 540 million years old are significantly different anatomically than every known specimen that is older than they are. Meanwhile, every known specimen I’ve seen that is about 540 million years old is at least fairly similar anatomically to at least one known specimen that is older than it. For instance, there is no known wolverine specimen that is 600 million years old. Some point to trilobites as being an example of a known specimen that is significantly different than every known specimen older than them. But that is not the case. Here is a link to some trilobite specimens:

http://www.fossilmuseum.net/Fossil_[…]lichiida.htm

And here is a link to spriggina floundersi, a specimen that is about 630 million years old:

http://www.paleobase.com/gallery/me[…]riggina1.jpg

In addition, the phrase “Cambrian explosion” is misleading.

It sure is. Dynomite was not invented until 1866, and even gunpowder is believed to be invented in the 9th century, so if someone proposes an explosion in the Cambrian they need to come up with a plausible mechanism.

Are you sure about the reference for the Peterson et al paper? When I go to that issue of Paleobiology, I don’t find it there.

Lee J Rickard wrote: Are you sure about the reference for the Peterson et al paper? When I go to that issue of Paleobiology, I don’t find it there.

It’s in the supplement. You can get the pdf here.

Perhaps the Bombardier beetle was around at the end of the Ediacarian!

That would explode!!!!

Perhaps the Bombardier beetle was around at the end of the Ediacarian!

That would explode!!!!

It would be nice if this were published somewhere outside the internet. NCSE Reports or one of the skeptics magazines would be good. Great job!

I’m glad I put this off until today so I could take a while and really enjoy it. Excellent article, Mr Meurs.

-Schmitt.

I am glad to hear that people like it. I am quite interested in the Cambrian explosion and I was hoping to share some of my recent research in this area. I was reluctant to post since it was somewhat rough and in places unfinished but I have other obligations to tend to and it was either delay it for several weeks or post as is.

There is so much (recent) work on the Cambrian, much of which rebuts the common creationist arguments, that I hope that people interested in this topic will take the time and effort to explore further themselves.

But even more I hope that creationists will take home a valuable lesson from this namely that it is important to double check the claims made. In case of the Cambrian, creationist claims have become untenable.

Of course because of the abrupt nature of the Cambrian, at least in the mind of creationists (the Cambrian is longer than the time we split from other apes), creationists are quick to jump to a conclusion of ‘abrupt creation’. After all the definition of intelligent design/creationism is, according to of Pandas and People:

“Intelligent design means that various forms of life began abruptly through an intelligent agency, with their distinctive features already intact.”

Guess another one bites the dust but the Cambrian period, or at least the creationist strawman version, plays a big role in defining ‘intelligent design’. And as such, the failures of the Cambrian to live up to Creationist expectations plays a big role in exposing the scientific vacuity of ID.

Here’s a question – is there a book (doesn’t matter if it’s expensive) that has descriptions of nearly all the Cambrian fossils found so far with lots and lots of pictures? It would be nice, if someone claims that all variety appeared in an “explosion” and everything else is just change within kinds, to pull out this book and say, “Here are all the Cambrian organisms, thumb through this and see if you can find anything at all that we see around us now, see if you can tell which modern kind each one belongs to.” This rebuttal hits the sore point of human origins – if they claim that creation happened back then, I’d like to see them try to say which of these swimming beasties is the “kind” of humans. If it bothers them to think that our ancestors were apelike, how much worse to have ancestors sort of like floppy fish!

Valentine’s “On the Origin of Phyla” 2004 has many drawings but I am not sure if the book is exhaustive. Often one has to piece together the details from papers etc.

Creationists, who are quick to quote Valentine, somehow seem to have missed his latest work, culminating in his opus.

Burgess shale pictures

Fauna and Flora of the Burgess Shale

Cambrian

Phylum level evolution by Glenn Morton

The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life

Images for Chapter 5 The Cambrian Explosion

I have been lurking for a long time, and was finally moved to post a comment. Thank you for your hard work. I start yelling at the computer/radio/newspaper when I read about creationist ignorance and stupidity. The patience it must take to read through all their garbage and then write detailed refutations is amazing. This isn’t just for PvM, but for everyone who works on Pandasthumb and the associated blogs. Ya’ll do great work.

Cheers John

I too have been a lurker for some time now and I learned a good deal from your article. I am not a biologist but it doesn’t take me any time to dismiss the creationists’ claims. I really don’t read much of the stuff that you write about the ID crowd. As a non-biologist I am more interested in posts such as this. I understand this took a lot of effort on your part and three cheers for that.

I’m sure someone has already done this, but what about a calculation as to what “sudden” actually means in geologic time? I think laypeople forget (or don’t know) just how huge a period of time is represented by these fossil changes, particularly as a ratio to the reproductive time of the organisms. How many generations (some reasonable approximation) elapsed between say, the Ediacarian fauna and the Cambrian? And (cross-reference to the “bacterial genome” thread on PT http://www.pandasthumb.org/archives[…]diversi.html) since a marginal beneficial mutation spreads rapidly in a population, morphological change should be pretty easy in those time-frames.

This will only work, of course, for OEC arguments. YEC need not apply.

Good point. I wouldn’t think that the “generation” for a horseshoe crab or a lobster could be much more than a year or few, but let’s call it two years, which would mean something on the order of 500,00 (and perhaps more likely a million-plus) generations per million years.

Using 20-year generations for recent hominids like ourselves, 500,000 generations would take us back to, what, 10 million years ago–or well before the human-chimp-gorilla lineages split. If the arthropods of those more distant days had “only” 10 million years to play with–and of course there’s now good reason to believe multicellular animals had been “in development” for much longer than that, perhaps even for hundreds of millions of years!–then we’re talking 5,000,000 of their generations, right? Lots of time for beaucoup mutations to arise and for the favorable ones to spread.

It’s dubious as we get back to our primate and proto-primate and early mammal ancestors that using 20-year human generations makes any sense. If we instead use a small-to-medium-sized mammal “generation” of a year or two for the 4.5M generations that preceded the latest 500K generations leading to ourselves, then a total of 5M proto-human generations (corresponding now to our estimate for the early arthropods over the span of “Cambrian explosion” time) would take us back a total of 15 to 20M years. And that might roughly correspond to, what, the ape-monkey split?

So, if 5M proto-human generations covers ALL the ape and hominid lineages–and every other species of modern or “recently” extinct mammal, bird, lizard, turtle, frog, snake, fish, insect, plant, etc., that has lived and died for the last 15-20M years, and if that fossil assemblage was the one that was isolated and scrutinized, I suspect the term “explosion” might seem equally appropriate.

Except, of course, we have a lengthy series of fossil precursors for all the more recent critturs, so the creato-IDiots are never forced to make that comparison.

I think folks also tend to forget that the entire assemblage of multicellualr animals in the pre-Cambrian/Cambrian timeframe was much smaller, the entire “animal” ecology probably consisted of a few hundred meters of coastal waters fringing the continents, and–while representative of most (but not all!) of the current “phyla” had appeared on the stage, those phyla were hardly jam-packed with representatives–unlike today.

In these circumstances, any favorable adaptation by any of the main players would, it seems to me, force a major-ly ratcheting arms’ race by all the other players. Sounds like a recipe for “rapid” generation of novelties to me.

Re “but what about a calculation as to what “sudden” actually means in geologic time?” Re “How many generations (some reasonable approximation) elapsed between say, the Ediacarian fauna and the Cambrian?”

A search on http://www.talkorigins.org/ for “geologic timeline” gave Geological Time Scale

Evolutionary and Geological Timelines

That says 580-545mya - Fossils of Ediacaran organisms are made and 545mya - Cambrian explosion of hard-bodied organisms. Although, I thought the “explosion” was now thought to have taken several million years and that table gives it only the one number, not a range.

But, I would expect those 35 my (580-545) would likely be well over 35 million generations for most species.

Henry

Re “while representative of most (but not all!) of the current “phyla” had appeared on the stage,”

It’s funny how Creationists can take the point that most phyla had precursors in that period and try to make like that’s somehow a “problem”. Of course they all had precursors - that’s what the theory says, lol. The only variable is which of the precursors would be polite enough to leave fossil traces of itself for people to find a half billion years later.

Re “In these circumstances, any favorable adaptation by any of the main players would, it seems to me, force a major-ly ratcheting arms’ race by all the other players. Sounds like a recipe for “rapid” generation of novelties to me.”

That’s my take on it, too. I don’t know if the trigger adaptation was eyes, armor, manipulators, mobility, or what, but it strikes me as likely to have been something along one of those lines.

Henry

That’s a very nice summary of recent work. Is it available in PDF format?

About this Entry

This page contains a single entry by PvM published on October 12, 2005 9:46 PM.

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