The Cambrian as an evolutionary exemplar

| 22 Comments
Cambrian timeline

I've been reading Valentine's On the Origin of Phyla(amzn/b&n/abe/pwll) lately, and I have to tell you, it's a hard slog. This is one of those extremely information-dense science texts that rather gracelessly hammers you with the data and difficult concepts on page after page. I am convinced that James W. Valentine is ten times smarter than I am and knows ten thousand times as much, and it's a struggle to squeeze that volume of knowledge into my miniscule brain pan.

One thing I would like to greatly condense and simplify is his discussion of the Cambrian 'explosion'. Misinterpretation of the Cambrian is one of the many prongs of the creationist assault on science; both old school Biblical creationists and the new stealth creationists of the ID movement have seized upon it as evidence of an abrupt creation—that a Designer poofed the precursors to all modern forms into existence suddenly, and without precursors, and that this observation contradicts evolutionary theory.

It doesn't. Valentine has an excellent diagram that shows how wrong the creationists are.

Continue reading "The Cambrian as an evolutionary exemplar" (on Pharyngula)

22 Comments

The kings of creation at this time were scattered beasties the size of a baby’s toenail, but still, it was a step upward in size and durability from what had come before.

Maybe they weren’t the kings:

Proterozoic modular biomineralized metazoan from the Nama Group, Namibia.

Wood RA, Grotzinger JP, Dickson JA. Science. 2002 Jun 28;296(5577):2383-6.

We describe a Proterozoic, fully biomineralized metazoan from the Omkyk Member (approximately 549 million years before the present) of the northern Nama Group, Namibia. Namapoikia rietoogensis gen. et sp. nov. is up to 1 meter in diameter and bears a complex and robust biomineralized skeleton; it probably represents a cnidarian or poriferan. Namapoikia encrusts perpendicular to the walls of vertical synsedimentary fissures in microbial reefs. This finding implies that large, modular metazoans with biologically controlled mineralization appeared some 15 million years earlier than previously documented.

Pubmed

Excellent posting. Why ID creationists are still using Valentine’s earlier work and ignore his book is somewhat puzzling to me.

Pete Dunkelberg Wrote:

up to 1 meter in diameter

Yowza!

There is something deceitful about most the nonsense written on the Cambrian Explosion, as YECs simply deny geological time and IDiots just ignore it. The explosion took one hell of a long time!

This confirms to me that the most improtant scientific argument to get across is the vast age of the earth and the universe. Evolution should always take second place - I will get my knuckles wrapped for this! When dealing with YECs I seek to convince them that the earth is old - a few million will do. You have then destroyed all the main theolgical planks of YEC and evolution might come later

PS I mapped a few thousand sq miles of late Precambrian in the Richtersveld, just inside South Africa years ago, which was older than the Nama and included the Numees tillite in which I found a stromatolite in associated dolomite, and also a dropstone and varves. I still wonder if I walked over some nice fossils which I didnt see because I wasnt looking. I lived for six months at Numees in a caravan while assessing the viability of the Numees copper mine,

Syntax Error: not well-formed (invalid token) at line 1, column 63, byte 63 at /usr/local/lib/perl5/site_perl/5.12.3/mach/XML/Parser.pm line 187

I was looking at Pharyngula and found this ;

Atheist Revolution: Religious belief is a destructive force that causes far more harm than good. Atheist Revolution is a blog dedicated to breaking free from irrational belief and opposing Christian extremism in America.

Now what IS interesting is the beleifs of Adam Sedgwick who first sorted out the Cambrian in the days after Darwin left him on 21st August 1831 somewhere around Bangor. He was an Evangelical Christian and an ordained cleric in the Church of England. He also wasnt very good at fossils but identified quite a few. I have retraced many of the routes he did in North wales in 1831 (as I did all Darwins) and his longest route was 18 miles in the mountains (Carneddau) with over 6000ft of climbing. It took me over 10hours walking flat-out with my dog.

Now was Sedgwick irrational or not?

> God sits around. Hmmm, he thinks, I’m a bit bored today, what shall I do? I know, lets magically poof Wiwaxia into existence. That was fun, now I think I’ll sit around for a few hundred thousand years. Dum de dum (twiddles thumbs), la de da. By eck thinks God (God is a Yorkshireman you see), I haven’t done any creating for a while, I think its time to create Lingulella. Phew, I’m tired now; time for another break. Etc etc.

And according to Behe, God created insects and then waited millenia before creating plants – I guess he got annoyed by the hungry clacking of their empty mouthparts.

At the era of the Cambrian, are there any estimates as to the average livespan of these creatures? A few years on the long side, or way shorter? It seems to me, with no data whatsoever, so I’d be better off speculating my entire equity on DrKoop.com than saying this, but might the “cambrian explosion” be a reaction to a rapid ecological change? Or response to?

I was thinking in regards to chaos theory where a periodic occilation, but not quite exactly periodic, suddenly shifts, the example being heart arythmia. Thus, a very long stable period of conditions suddenly yields to a change that puts pressure on species present.

And, finally, are there other “explosions” or little bangs, even, in response to similar changes?

YEC: There was no Cambrian. IDC: God was more active in the Cambrian than at other times including the present.

Re “but might the “cambrian explosion” be a reaction to a rapid ecological change? Or response to?”

Something I read not too long ago (might have been on this blog or TalkOrigins archive) suggested that the “explosion” might have followed from some species developing vision, and thus finding its prey quicker than everybody else. So everybody else suddenly had to either catch (develop defenses of some sort) up or go bye bye. Sounds plausible.

Henry

Andrew Parker’s “In the Blink of an Eye” makes that argument. I read it some time ago and wasn’t much impressed. I’d give the Amazon URL, but I haven’t figured out the latest incarnation of KwickWhatsit tags.

Just type the URL, e.g., http://www.amazon.com Or you can get fancy (the quotes are necessary):

<url href="http://www.amazon.com">click here for the amazon link</url>

click here for the amazon link

Actually you can be fancier:

<url href="amazon://ASIN">click here for the amazon link</url>

Where “ASIN” is the ASIN of the book you want. It even inserts the TOAF referer code.

<url href="amazon://0738206075">In the Blink of an Eye</url>

In the Blink of an Eye

So can we have a link to page describing the syntax? :-)

PvM wrote:

Why ID creationists are still using Valentine’s earlier work and ignore his book is somewhat puzzling to me.

For all I know, they may be ignoring its contents, but they aren’t ignoring the book per se, and in fact, sell it on their website.

RBH said:

Andrew Parker’s “In the Blink of an Eye” makes that argument. I read it some time ago and wasn’t much impressed.

I just read it this summer (a little light beach reading), and I was actually fairly impressed. Parker is no Dawkins or Ridley in terms of prose style, so the book is a little dry perhaps, but I think he makes a good case.

Even if you don’t fully buy the thesis (“The Light-Switch Theory” he calls it), it’s still full of interesting facts about the broad diversity of solutions animals have found to the problems of seeing and being seen.

Clarified my thinking on the Cambrian Explosion, too.

PvM wrote: “Excellent posting. Why ID creationists are still using Valentine’s earlier work and ignore his book is somewhat puzzling to me.”

Are you also “puzzled” why they frequently cite Michael Denton’s 1985 book “Evolution, a Theory in Crisis,” yet almost always ignore his 1998 book “Nature’s Destiny”?

Ah. Then the hypothesis (of development of visual sense as driver) isn’t widely accepted. Then again, wouldn’t have to be vision - seems like anything that improves hunting ability (or evading ability) in one species would put pressure on the others to develop something to counter it. Seems like that could produce the sort of positive feedback loop that seems to be involved.

I wonder if an increase in the oxygen level might have had something to do with it. (Or more generally, increase availability of any important resource.)

Henry

Ah. Then the hypothesis (of development of visual sense as driver) isn’t widely accepted. Then again, wouldn’t have to be vision - seems like anything that improves hunting ability (or evading ability) in one species would put pressure on the others to develop something to counter it. Seems like that could produce the sort of positive feedback loop that seems to be involved.

I wonder if an increase in the oxygen level might have had something to do with it. (Or more generally, increase availability of any important resource.)

Henry

Mhm, but what improves hunting (or evading) ability like vision? One of the more interesting arguments in the book, especially since, as is described to some extent in the posting here, it is the sudden appearance of hard parts in the fossil record that are the hallmark of the “explosion” more than the sudden emergence of whole phyla, is summed up by Parker in the phrase “armament is ornamnent.” As regards oxygen levels or other metabolic/economic drivers of the event, Parker takes some pains to extole the virtues of his theory over others. All in all, it seems eminently plausible to me, if a little hard to meaningfully test.

Re “but what improves hunting (or evading) ability like vision?”

Well, I don’t know that other developments would be like vision specifically, but I can think of a bunch of things that would increase efficiency or effectiveness - armor, claws, teeth, running (or swimming) faster, improvement in other senses (hearing, smelling), poison injection, camouflage (against others that have vision), something to act as bait. Or any combination of those.

Henry

This leads to an interesting question - are there animals who use non-visual camouflage? For example, moths camouflaged against bat’s sonar?

I just happened to read passage in Grimaldi and Engel’s new book Evolution of the Insects that deals with something like non-visual camouflage.

Tiger moths have sound producing organs whose output may serve to jam bat sonar. But these moths are toxic because of the plant chemical ingested by their larva so the high-frequency sounds they emit may actually be more analogous to the bright colors of poisonous butterflies and stinging wasps, a way of warning off predators.

By the way, the Grimaldi and Engel book is absolutely splendid.

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This page contains a single entry by PZ Myers published on August 14, 2005 1:02 PM.

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