Jason Crowley

Dr. Pleins

Research Paper 1

February 6, 2003

 

The Cambrian Explosion: Proof of ID?

           

            In our studies of Intelligent Design (ID) theory and Creation Science, I found little information that seriously challenged the theory of evolution.  However, there was one event that appeared to defy the logic of Darwinian gradualism: the Cambrian Explosion.  This event was presented by ID theorists as proof of design--something which science is unable to account for.  Unfortunately for ID proponents, this is not the case.  There are several scientific explanations for the Cambrian Explosion.  I will give an account of the Cambrian Explosion, present the ID arguments relating to it, and give some scientific explanations of the event.

            The so called ‘Cambrian Explosion’ was a period of rapid diversification of animal life on earth.  It took place approximately 550 million years ago (it bears mentioning that estimations of geological time this far back are fairly rough).  There is some dispute over just how long the ‘explosion’ lasted.  Scientists traditionally proposed a duration of about 30 million years (Ward and Brownlee, p. 137).  However, some new evidence collected in Russia may indicate a much shorter timescale- 5 to 10 million years (Kerr 1993, p. 1274). 

            The truly unique thing about the Cambrian Explosion was the rapid generation of extremely diverse life forms.  Life is generally classified with a system going from broad to specific description.  Kingdom, the broadest classification, describes whether a given specimen is plant, animal, fungi, protist, or moneran.  The next most specific indicator is phylum.  The phyla indicate the body design of a taxonomical specimen.  Humans, along with all other species that poses a spinal chord of some description, are placed in the phylum Chordata.  During the Cambrian Explosion, all of the extant phyla--except, perhaps, one or two--came into existence.  ID proponents are fond of distorting this type of statement.  They will say that all of the ‘body plans’ originated in the Cambrian Explosion.  Such language seems similar to the Creationist word ‘kind.’  ID theorists would have you believe that the body plans of the species we see today existed 550 million years ago.  This is, of course, wrong.  To say that a phylum is a ‘body plan’ is in some ways accurate.  However, saying that a human and a dog have the same body plan seems mistaken--though they are both members of Chordata.  It is interesting to note here the amazing level of diversity generated in the Cambrian Explosion.  Today, there are between 28 and 35 distinct phyla.  Some paleontologists distinguish up to 100 separate phyla for the Cambrian Explosion! (Ward and Brownlee, pp. 141-42). 

            So, the question that everyone wants to answer is: “Why did the Cambrian Explosion happen?”  Intelligent Design proponents argue, of course, that it came about through the interference of some outside force.  They say that the rapid appearance of diverse life cannot be predicted by traditional evolutionary theory.  They claim that there are no fossilized forms from the Precambrian period.  They go on to say that there are three main arguments that evolutionists pose for the paucity of fossil evidence from the Precambrian:  “1.  There were evolutionary ancestors before the Cambrian Explosion, however they were all soft-bodied animals and thus could not be preserved as fossils…2. The Precambrian ancestors existed, but were too small to be preserved…3.  The evolution was rapid so transitional forms didn’t have time to be preserved.” (IDEA Center).  In response to the first argument, ID theorists say “imprints of soft-bodied animals are very commonly preserved as fossil remains very commonly in the fossil record” (IDEA Center).  To the second argument, they say “Small animals are very commonly fossilized throughout the fossil record…How can anyone argue that the size of the fossil makes it unpreservable?” (IDEA Center).  I need not go on to the third argument because the ID proponents are correct in their first two ‘counter-arguments.’  The trouble is, evolutionary scientists do not make the above arguments for the paucity of the fossil record.  Why don’t they?  Because they have evidence of fossilized Precambrian fauna--and have had it for the past fifty years (McMenamin and McMenamin, pp. 16-17).  ID theorists seem a little behind in the reading.

            Back in the 1940s, there was an Australian geologist named R.C. Sprigg working in a fossil bed in a fairly remote part of Australia.  Before I go on, it seems important to say that there are two types of fossils.  There are “body fossils” and there are “trace” fossils.  Body fossils are the kinds we think of most often--they are the fossilized body parts of prehistoric creatures.  An example would be the skeleton of a T-Rex in a museum.  Trace fossils on the other hand, are created when an organism makes an impression in the earth.  An example would be a footprint (McMenamin and McMenamin, pp. 14-16).  Now back to that Aussie bloke.  He was digging around and found numerous specimens of Precambrian fossils, nearly all of them were trace fossils.  The impressions left behind were very similar to two phyla we see today: Cnidarians and Annelids.  Cnidarians are essentially jellyfish, sea-pins and anemones.  Annelids are various types of worms.  These fossils represented proof that there was multi-cellular prior to the Cambrian Explosion.  This lent credence to the traditional gradualist evolutionary approach. 

            So a fossil record of Precambrian time has been established.  But the question remains, “What caused the sudden onset of evolutionary innovation?”  Given the current rates of genetic mutation, there is only a change of 1% in the DNA base sequences per 10 million years.  A 1% change would hardly account for the rapid diversification of animal life during the Cambrian Explosion (Ohno, p. 8475). Scientists have posed numerous theories as to how these changes may have occurred.  I will go into a few of them.  They are generally classified as either ecological explanations or biological explanations.

            The most widely held ecological explanation is the ‘oxygen threshold’ theory.  A certain level of oxygen must be present in the atmosphere before animals can be adequately sustained.  It took a long time for the oxygen levels to build to a level suitable for animals.  Animals need oxygen because “In the absence of abundant oxygen, organisms have a great deal of difficulty precipitation minerals as skeletal structures” (Ward and Brownlee, p. 143).  The oxygen threshold hypothesis also rather neatly explains why soft-bodied animals existed in the Precambrian, but few hard-bodied animals did. 

            Another well regarded ecological theory is that nutrients essential for animal life were suddenly made available during the time of the Cambrian Explosion.  Near the end of the Precambrian period, a super-continent, Rodinia, was in a great deal of turmoil.  Tectonic movements were tearing Rodinia apart, and in the process the global ocean currents were changed.  Deep water flowed to the surface, and nutrients that were never available before suddenly became accessible.  Of these nutrients, phosphorus and nitrate were the most important, because they are necessary for life (McMenamin and McMenamin, pp.92-105). 

            Yet another theory is that the climate of the earth became warmer at about the time of the Cambrian Explosion.  There was a long period of glaciation in the Precambrian.  Then the ice began to melt and life began to appear.  Some scientists are uncomfortable with this theory because they are unsure of any real relationship between the ends of glacial periods and the onset of life diversification.

            A final ecological theory has been suggested.  It is rather bizarre, and should be taken with a grain of salt.  Essentially, the theory goes something like this.  The earth is primarily liquid inside.  But it is solid on the outside.  Because tectonic plates like to move around, sometimes they build up in places where they shouldn’t.  When this happens, there is too much mass on one portion of the solid crust, and the whole thing slides to compensate.  This is called an ‘Inertial Interchange Event.’  So continents that were once at the poles could suddenly ‘slide’ to the equator, and visa versa.  The implications that such an event would have on the global environment are obvious.  It is suggested that an IIE occurred about 550 million years ago and it triggered the Cambrian Explosion (Ward and Brownlee, pp. 144-147).

            The biological explanations for the Cambrian Explosion tend to be less widely supported than the ecological explanations.  Often, the biological theories need to be viewed in conjunction with ecological theories in order for them to make sense. 

            The primary biological theory is what McMenamin calls the “green genes” hypothesis (McMenamin and McMenamin, p. 169).  This theory states that genes today are not as flexible as they used to be.  In the past, it was easy for genes to reconfigure themselves to fit new niches, but over time they have become locked into certain pathways because of their success.  The metaphor of a stream is often used to explain this model.  In the beginning, it is easy to redirect the water.  But as the stream cuts a trench in the earth, it becomes increasingly difficult to change its flow. 

            There are several other biological theories.  One suggests that life could not diversify until the physiological advent of the skeleton.  This theory needs to be taken in conjunction with the oxygen threshold theory.  Some suggest that there was a critical-mass, so to speak, of physiological complexity.  Once that point was reached, life could freely vary.  Another theory is that organisms developed the ability to reproduce sexually.  This allowed for an increased shuffling of genes, which led to increased variation (Kerr 1995, p. 33). 

            A final theory is the ‘Garden of Ediacara’ theory (Ediacara is the name of the place that Sprigg first discovered Precambrian fossils).  This theory suggests that there was a period where there were no predators.  The Ediacaran life forms originally discovered by Sprigg lived during this period, in the Precambrian.  But predators of some sort eventually evolved, killing off most of the Ediacarans.  Those that were able to form shells to protect themselves, or burrow to hide from the predators, survived.  They also, accidentally, found new feeding sources that were previously untapped.  Thus, natural selection got started and organisms quickly adapted to new niches (McMenamin and McMenamin, pp. 106-26).

            There is one major question remaining regarding the Cambrian Explosion.  Since that amazing event 550 million years ago, no new phyla have evolved.  Why not?  Scientists seem to have come up with only one real answer: there isn’t enough room.  When the Cambrian Explosion happened, there were numerous niches that organisms could evolve to fill quickly because of a relative lack of competition.  But once all of the biological roles were filled, there was no more reason for innovative adaptation.  There have been mass-extinctions in the past, even one that killed nearly 95% of all marine life.  But none of these catastrophes returned the diversity of life to its Precambrian levels.  That is why we do not observe biological diversification of the level seen during the Cambrian Explosion at any other time in geological history (Kerr 1994, p. 1163). 

            I was initially drawn to the Cambrian Explosion because Intelligent Design theorists had presented it as irrefutable proof of a designer.  But after looking into the matter, it seems more like the Cambrian Explosion is a proving ground for evolutionary theory.  Rather than a paucity of Precambrian fossil evidence, there is an abundance of it.  Rather than throwing in the towel when faced with the rapid appearance of biological variation, scientists have come up with numerous theories explaining how the explosion of life could have happened.  In all of this, I find myself disillusioned by the ID proponents.  It seems that they too often distort the facts, or outright lie, to ‘prove’ their position.  How can there ever be a valid search for truth if information is intentionally withheld or misrepresented? 

 


 

Works Cited

 

Kerr, Richard A.  Evolution’s Big Bang Gets Even More Explosive.  Science, New Series

            Volume 261, Issue 5126.  September 3, 1993.

 

Kerr, Richard A.  Crowding Innovation out of Evolution.  Science, New Series,

            Volume 266, Issue 5188. November 18, 1994.

 

Kerr, Richard A.  Timing Evolution’s Early Bursts.  Science, New Series, Volume 267,

            Issue 5194.  January 6, 1995.

 

McMenamin and McMenamin.  The Emergence of Animals: The Cambrian

            Breakthrough.  Columbia University Press, New York.  1990.

 

Ohno, Susumu.  The Notion of the Cambrian Pananimalia Genome.  Proceedings of the

            National Academy of Sciences of the United States of America, Volume 63,

            Issue 16.  August 6, 1996.

 

Ward and Brownlee.  Rare Earth: Why Complex Life is Uncommon in the Universe.

            Copernicus, New York.  2000.