A few paragraphs and already so many errors. I have numbered the claims so that I can reference them in my response. But let's first address the fascination of the creationists with the Cambrian explosion.Los Angeles-based filmmaker, Illustra Media best known for The Privileged Planet, whose showing at the Smithsonian took "uproar" to a whole new level, is now working on a documentary The Cambrian Explosion: "The Cambrian Explosion will examine what many consider to be, the single most powerful refutation of Darwinian evolution---the fossil record [1]. When he wrote his book, Charles Darwin realized that the 19th century fossil record did not support his theory of gradual, step-by-step evolutionary change[2]. Yet, he hoped that future generations of scientists would make the discoveries necessary to substantiate his ideas. Today, after more than 150 years of digging, fossil evidence of slow, incremental biological change does not exist [3]. Instead, we find a pattern of rapid, dramatic appearances of fully developed, complex organisms in the ancient rock strata of the world[4]. A pattern that is best explained by the work of a transcendent intelligence." [5]
— Denyse
Kitzmiller complaint The Cambrian explosion as an abrupt appearance combined with the 'teach the controversy'/'teach alternatives to evolution' are well established creationist arguments. Intelligent design is not much different here. What is surprising to me is that ID still accepts the flawed creationist arguments about the Cambrian explosion. But given the importance of 'abrupt appearances' to 'creation science' perhaps this is not too surprising.Dr. Kenyon submitted an affidavit in support of the Louisiana law at issue in Edwards v. Aguillard, that described "creation science" as "origin through abrupt appearance in complex form" and stated that "creation-science and evolution are the sole scientific alternative explanations" of the origins of life.
— Kitzmiller complaint
Typically, creationist discussions of the Cambrian rely on quotes made by scientists 20 or more years ago, which in the fast paced research of the Cambrian, makes them quickly outdated. Since the Cambrian Explosion is a commonly abused concept, I will use this opportunity to share some of the recent research in this area which, not surprisingly, contradicts much of the creationist claims. For instance, Denyse on her blog quotes from VeritasWell, this should be interesting. What you never heard about the Cambrian explosion is mostly surprising. While I am here, I may as well shill books on the subject: Stephen Jay Gould's Wonderful Life and Simon Conway Morris's The Crucible of Creation are both good reads, in my experience. (Consumer intellectual safety warning: These books take opposite positions on key issues. Intellectual freedom required. The Darwinian thoughtbot suffered an engineered mishap this afternoon, while mistakenly left in O'Leary's thoughtful care, so
— Denyse
1982...Wow... To give an example of how fast science moves, ID proponents have been quite willing to quote Valentine's earlier statements on the Cambrian (see for instance the above link referenced by Denyse which quotes Valentine), while somehow ignoring his recent major opus "On the origin of Phyla" in which he is clear about the link between the Cambrian and Darwinian theory.The record jumps, and all the evidence shows that the record is real: the gaps we see reflect real events in life's history -- not the artifact of a poor fossil record. Eldredge, N. and Tattersall, I. (1982) The Myths of Human Evolution Columbia University Press, p. 59
— Denyse
So will the Cambrian "sink the ship of Darwinism", as Denyse puts it? I doubt it although one may easily be confused about the Cambrian explosion when relying on old quotes and creationist resources. But if ID relies on poor science to support it claims of faith (transcedental (read supernatural) intelligence), it may very well sink religious faith and do a major disservice to scientific education. ASA has some excellent resources as well which address not only the problems in creationist claims about the Cambrian but also show how science is slowly resolving the various questions The Precambrian to Cambrian Fossil Record and Transitional Forms by Keith B. Miller Miller explains the confusion so common amongst creationist about the 'top down fallacy". In this case specifically Battson (who is at the center of a 'controversy' ) and his article "on the origin of stasis". Many of the figures in this paper are wrong, which may be partially due to the fact that this article was written over 7 years ago but the confusion created by these figures seems to remain prevalent amongst creationists.The title of this book, modeled on that of the greatest biological work ever written, is in homage to the greatest biologist who has ever lived. Darwin himself puzzled over but could not cover the ground that is reviewed here, simply because the relevant fossils, genes, and their molecules, end even the body plans of many of the phyla, were quite unknown in his day. Nevertheless, the evidence from these many additional souces of data simply confirm that Darwin was correct in his conclusions that all living things have descended from a commmon anscestor and can be placed within a tree of life, and that the principle process guiding their descent has been natural selection. (Valentine On the Origin of Phyla 2004: Preface)
— Valentine
A recent paper shows why some of the objections by for instance Stephen Jay Gould in "Wonderful life" have been resolved by recent findings. Derek E. G. Briggs and Richard A. Fortey Wonderful strife: systematics, stem groups, and the phylogenetic signal of the Cambrian radiation Paleobiology; June 2005; v. 31; no. 2_Suppl; p. 94-112Battson emphasizes the pattern of appearance of higher taxa in which phylum-level diversity reaches its peak in the fossil record before class-level diversity, and class-level diversity before that of orders, etc.10 Battson and other critics of macroevolution interpret this apparent "top-down" pattern as contrary to expectations from evolutionary theory. However, this pattern is generated by the way in which species are assigned to higher taxa. When a hierarchical classification is applied retrospectively to a diversifying evolutionary tree, a "top-down" pattern will of necessity result. Consider, for example, species belonging to a single evolving lineage given genus-level status. This genus is then grouped with other closely related lineages into a family. The common ancestors of these genera are by definition included within that family. Those ancestors must logically be older than any of the other species within the family. Thus the family level taxon would appear in the fossil record before most of the genera and species included within it. The "top-down" pattern of taxa appearance is therefore entirely consistent with a branching tree of life.
— Keith Miller
Much has been made of this disparity/diversity argument and creationists have used our ignorance about the details of events which took place over 500 million years as evidence not only against Darwinian theory but also in favor of intelligent design. Sadly enough, this gap argument has not done much better than other creationist arguments. Hard work by paleontologists have resolved many of the issues that puzzled early researchers. The paper above also discusses the problem of the concept of a phylum, which is highly artificial and has lead to much confusion. And much has changed since 1989, not only because of some excellently preserved fossil finds from the " Lower Cambrian of Chengjiang in southwest China, the Sirius Passet fauna of North Greenland, and the Upper Cambrian phosphatized "Orsten" of southern Sweden and elsewhere" The authors concludeGould's Wonderful Life (1989) was a landmark in the investigation of the Cambrian radiation. Gould argued that a number of experimental body plans ("problematica") had evolved only to become extinct, and that the Cambrian was a time of special fecundity in animal design. He focused attention on the meaning and significance of morphological disparity versus diversity, and provoked attempts to quantify disparity as an evolutionary metric. He used the Burgess Shale as a springboard to emphasize the important role of contingency in evolution, an idea that he reiterated for the next 13 years. These ideas set the agenda for much subsequent research. Since 1989 cladistic analyses have accommodated most of the problematic Cambrian taxa as stem groups of living taxa. Morphological disparity has been shown to be similar in Cambrian times as now. Konservat-Lagerstätten other than the Burgess Shale have yielded important new discoveries, particularly of arthropods and chordates, which have extended the range of recognized major clades still further back in time. The objective definition of a phylum remains controversial and may be impossible: it can be defined in terms of crown or total group, but the former reveals little about the Cambrian radiation. Divergence times of the major groups remain to be resolved, although molecular and fossil dates are coming closer. Although "superphyla" may have diverged deep in the Proterozoic, "explosive" evolution of these clades near the base of the Cambrian remains a possibility. The fossil record remains a critical source of data on the early evolution of multicellular organisms.
In other words, science has resolved many but not all of the questions raised, many still remain under debate. But at least a few common misconceptions have been resolved:Gould's Wonderful Life (1989) was an inspiration to students and served to set the agenda for 15 years of intensive research on the meaning of the Cambrian evolutionary "explosion." New sources of data have arisen from several quarters---particularly the discovery of major new soft-bodied faunas from the Paleozoic and the application of molecular techniques to questions of phylogeny and divergence times. Many of the issues that Gould raised are still under debate---a number have attracted the attention of zoologists, paleontologists, and molecular biologists and fostered interdisciplinary interest in a way that should be a model for the future. Although some of the ideas in Wonderful Life have not stood the test of time, the challenges set have served to move the science forward.
The debates have also highlighted the arbitrariness of the concept of a phylum.Claims about strikingly elevated numbers of "new phyla" in the Cambrian have been countered. Cladistic analysis has placed the majority of Cambrian "weird wonders" as stem taxa of known clades. New fossil discoveries have resolved the problematic status of several former enigmas. Although new major extinct taxa (e.g., Phylum Vetulicolia [Shu et al. 2001b]) occasionally still appear in the literature, their erection is controversial and their objective basis unclear. Nor have claims about a maximum of morphological disparity in the Cambrian stood up to analysis. At most, disparity of design was equal to that at the Recent. Its range was established early and its compass shifted through time in total morphospace.
It seems clear that claims that the Cambrian explosion refutes Darwinian theory may have had some relevance when Darwin first proposed his ideas, Darwin himself wondered about the Silurian fossils. In fact, much of what we now know about the Cambrian has come to us through fossil finds and phylogenetic data in the last decade or less. These new data, rather than increasing the mystery, have shown how the Cambrian explosion falls well withing the evolutionary paradigm. There remain many unanswered questions, but given the success or lack thereof, of creationist arguments not only against Darwinian theory but also in favor of intelligent design, I hope that ID proponents will be more careful to use the gap argument to further their cause. It does not only do a disservice to science education but also to the religious faith of those who believe that the Cambrian shows scientific evidence not only against Darwinian theory, but also in favor of a supernatural designer. Logically speaking, this means that when science shows that the Cambrian is not really evidence against Darwinian theory and thus does not particularly favor or disfavor a supernatural designer, that the supernatural designer must have been disproven by science. The Cambrian explosion is a fascinating period in the history of evolution and will surely be the focal point of much scientific discussion but the portrayal of this period by creationists such as quoted by Denyse, does a major disfavor to science education, as it ignores easily verifiable facts.Debates about the Cambrian radiation have stimulated a debate over how "phyla" might be defined at all. One view bases a definition of phylum (or class) on the crown group and excludes stem taxa as plesions. This has the advantage of objectivity and ensures that molecular data are available for the whole taxon except where primitive survivors pull fossil taxa into the crown clade. The crown-group definition of a phylum is arbitrary, however, depending on the most primitive taxon that happens to have survived to the present day. An alternative view defines higher taxa on the basal divergence (total group), which is logically consistent, and assigns stem taxa to a phylum. A disadvantage is that the placing of extremely plesiomorphic forms, particularly those with peculiar autapomorphies, remains difficult.
Kevin J. Peterson, Mark A. McPeek, and David A. D. Evans Tempo and mode of early animal evolution: inferences from rocks, Hox, and molecular clocks, Paleobiology, 31(2), 2005, pp. 36--55A New Metazoan Time Frame. Using the topology in Figure 1 as our phylogenetic framework, and the high-precision geochronological dates reviewed above, we can now discuss the time frame for bilaterian evolution. The molecular clock is the tool of choice to test hypotheses of metazoan originations independent of the fossil record (Runnegar 1982). Although problems exist with certain aspects of molecular clock analyses (Smith and Peterson 2002; Benton and Ayala 2003), two recent analyses came to the same conclusion: bilaterians arose ca. 600--630 Ma, and nephrozoans arose ca. 560--580 Ma (Aris-Brosou and Yang 2002, 2003; Peterson et al. 2004; see each individual paper for details of the analyses and confidence intervals). The estimates from an updated analysis of Peterson et al. (2004; Peterson unpublished) are shown on Figure 2.
Blair et al argue that the divergence dates are much earlier.
Jaime E. Blair and S. Blair Hedges Molecular Clocks Do Not Support the Cambrian Explosion Molecular Biology and Evolution 2005 22(3):387-390
Another recent calculation finds some 'middle ground' Kevin J. Peterson and Nicholas J. Butterfield Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record. PNAS July 5, 2005 vol. 102 no. 27 9547-9552Abstract The fossil record has long supported the view that most animal phyla originated during a brief period approximately 520 MYA known as the Cambrian explosion. However, molecular data analyses over the past 3 decades have found deeper divergences among animals (~800 to 1,200 MYA), with and without the assumption of a global molecular clock. Recently, two studies have instead reported time estimates apparently consistent with the fossil record. Here, we demonstrate that methodological problems in these studies cast doubt on the accuracy and interpretations of the results obtained. In the study by Peterson et al., young time estimates were obtained because fossil calibrations were used as maximum limits rather than as minimum limits, and not because invertebrate calibrations were used. In the study by Aris-Brosou and Yang, young time estimates were obtained because of problems with rate models and other methods specific to the study, and not because Bayesian methods were used. This also led to many anomalous findings in their study, including a primate-rodent divergence at 320 MYA. With these results aside, molecular clocks continue to support a long period of animal evolution before the Cambrian explosion of fossils.
Blair and Hedges, not to be outdone, report
Jaime E. Blair and S. Blair Hedges Molecular Phylogeny and Divergence Times of Deuterostome Animals Molecular Biology and Evolution 2005 22(11):2275-2284
FIG. 4.--- A Bayesian timescale for deuterostome evolution. Divergence times for each node are presented in table 1. Global glaciations are hypothesized to have occurred approximately 750--700 MYA (Sturtian), 665--635 MYA (Marinoan), and 580 MYA (Varanger/Gaskiers) (Hoffmann et al. 2004). The Cambrian Explosion of fossils occurred approximately 543--520 MYA.
Of course, while it claims that the Cambrian present evidence of a supernatural designer, I doubt that such evidence will be explained in any significant detail. Which is why so many consider Intelligent Design scientifically vacuous. Not because it misunderstand science, that has been a common problem even amongst earlier creationists, but because it fails to provide any scientifically significant argument in favor of its claims.
Charles Darwin on the Cambrian (Silurian)
Darwin's quote is presented in more detail at the The Quote Mine Project Or, Lies, Damned Lies and Quote Mines: Darwin Quotes, at TalkOrigins. Jun-Yuan Chen, David J. Bottjer, Paola Oliveri, Stephen Q. Dornbos, Feng Gao, Seth Ruffins, Huimei Chi, Chia-Wei Li, Eric H. Davidson Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian Science, Vol 305, Issue 5681, 218-222, 9 July 2004For instance, I cannot doubt that all the Silurian trilobites have descended from some one crustacean, which must have lived long before the Silurian age, and which probably differed greatly from any known animal... Consequently, if my theory be true, it is indisputable that before the lowest Silurian stratum was deposited, long periods elapsed, as long as, or probably far longer than, the whole interval from the Silurian age to the present day; and that during these vast, yet quite unknown, periods of time, the world swarmed with living creatures. To the question why we do not find records of these vast primordial periods, I can give no satisfactory answer. Charles Darwin, The Origin of Species, 1859, p. 313-314
See alsoTen phosphatized specimens of a small (<180 micrometers) animal displaying clear bilaterian features have been recovered from the Doushantuo Formation, China, dating from 40 to 55 million years before the Cambrian. Seen in sections, this animal (Vernanimalcula guizhouena gen. et sp. nov.) had paired coeloms extending the length of the gut; paired external pits that could be sense organs; bilateral, anterior-posterior organization; a ventrally directed anterior mouth with thick walled pharynx; and a triploblastic structure. The structural complexity is that of an adult rather than a larval form. These fossils provide the first evidence confirming the phylogenetic inference that Bilateria arose well before the Cambrian.
Stefan Bengtson and Graham Budd Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian" Science 19 November 2004: 1291 Jun-Yuan Chen, Paola Oliveri, Eric Davidson, and David J. Bottjer Response to Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian" Science 19 November 2004: 1291
26 Comments
KiwiInOz · 13 October 2005
Thanks for this PvM - more ammo for the arsenal against the quacks.
NDT · 13 October 2005
Alan · 13 October 2005
Thanks PvM, PT at its best.
polio · 13 October 2005
"creation-science and evolution are the sole scientific alternative explanations"
But then, either ID is "creation-science", or it is unscientific, right? ;-)
Koly · 13 October 2005
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.
Michael Roberts · 13 October 2005
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
Bayesian Bouffant, FCD · 13 October 2005
Rocky · 13 October 2005
Outstanding info!
I love this site.
Longhorn · 13 October 2005
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_Galleries/TrilobitesRedlichiida.htm
And here is a link to spriggina floundersi, a specimen that is about 630 million years old:
http://www.paleobase.com/gallery/metas/Spriggina1.jpg
Descent & Dissent · 13 October 2005
Lee J Rickard · 13 October 2005
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.
Andrea Bottaro · 13 October 2005
Michael Roberts · 13 October 2005
Perhaps the Bombardier beetle was around at the end of the Ediacarian!
That would explode!!!!
Michael Roberts · 13 October 2005
Perhaps the Bombardier beetle was around at the end of the Ediacarian!
That would explode!!!!
Dan Phelps · 13 October 2005
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!
Schmitt. · 13 October 2005
I'm glad I put this off until today so I could take a while and really enjoy it. Excellent article, Mr Meurs.
-Schmitt.
PvM · 13 October 2005
Vasha · 13 October 2005
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!
PvM · 13 October 2005
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
john · 14 October 2005
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
Jav · 14 October 2005
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.
geogeek · 14 October 2005
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/2005/10/endless_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.
Steviepinhead · 14 October 2005
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.
Henry J · 14 October 2005
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
Henry J · 14 October 2005
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
Bayesian Bouffant, FCD · 20 October 2005
That's a very nice summary of recent work. Is it available in PDF format?