By: Paul Chien, Ph.D.
Fill-in-the-blanks and True or False:
1. The Cambrian Explosion also often referred to as "evolution's big bang," refers to the geologically "sudden appearance" of fossils which occurred approximately _____________________ years ago.
2. Assuming the earth to be four billion years old and the Cambrian Explosion to have lasted ten million years, then the percentage of the earth's age that the "Explosion" took was about ___________ percent, which would correspond to about _________ minutes in a 24-hour day.
3. The two countries where these fossils are found are _______________ and _____________.
4. The "explosion" of fossils found is problematic from an evolutionary standpoint because there have been no fossil ________________ found to link the major phyla together prior to that time.
5. True or False: Vertebrate fish are known from the Cambrian strata.
6. True or False: Some Chinese scientists have expressed serious doubts about evolutionary explanations of some aspects of the fossil record.
7. Cambrian strata contain representatives of more animal ____________ than any other geological period.
8. The Cambrian explosion implies a "top down" or "bottom up" history of the origin of animal biodiversity.
9. True or False: Most animal phyla appear in the fossil record after the Cambrian explosion.
10. True or False: The empirical evidence of the "sudden appearance" of fossils found in Chengjiang, China and the Burgess Shale, Canada is consistent with Intelligent Design Theory.
1. 530 million
2. 10 mil./4 bil. = .0025 or .25 percent, which corresponds to 3.6 minutes in a day
3. China and Canada.
8. "Top Down"
Further Comments regarding the Cambrian Explosion:
Evolutionists have typically tried to explain the Cambrian Explosion through some of the following explanations:
1. There were evolutionary ancestors before the Cambrian Explosion, however they were all soft- bodied animals and thus could not be preserved as fossils. The "Cambrian Explosion" is not actually the sudden evolution of animals, it just marks the first evolution of hard shell and bone parts which can be easily preserved.
Counter-argument: Obviously skeletons and shells are easier to preserve in rock than soft- flesh. However, imprints of soft-bodied animals are very common in the fossil record. Jellyfish, sea squirts, plants, sponges, and even bacteria are extremely common in the fossil record. Indeed, a good portion of the Cambrian Explosion fossils were soft-bodied animals, so how can one argue that previously, soft-bodied predecessors couldn't have been fossilized? Furthermore, much of the "Precambrian" rock, which would have been able to preserve these "missing ancestors" is actually very good rock for preserving delicate soft-bodied fossils.
2. The Precambrian ancestors existed, but were too small to be preserved.
Counter-argument: Similar to the above argument, small animals are very commonly fossilized throughout the fossil record. Even in the Cambrian Explosion fossils, very small organisms are not uncommon. Dr. Paul Chien has studied animals from this period at early microscopic stages of development. How can one argue that the size of the fossil makes it unpreservable? If the animals were there, they would have been preserved. If the animals were preserved, they would have been found. Since they are not found, the only conclusion is that the supposed ancestors were never there. Regardless, studies of the necessary predecessors show that they probably were not small nor simple. The proposed common ancestor of the two basic animal groups (protostomes and deuterostomes), thought to have existed about 1.2 billion years ago, had a gut cavity, regulatory genes, appendages (for locomotion or something else), a complex eye, and even a heart with a fluid system! This is hardly a microscopic primitive life-form. (See "Evolutionary explosions and the Phylogenetic fuse," in Tree, vol 13 no. 4 by Alan Cooper and Richard Fortey and "Early Animal Evolution: Emerging Views from Comparative Biology and Geology," Science, vol 284, June 25, 1999. By A. Knoll and S. B. Carroll.)
3. Small mutations in regulatory "Hox" genes allowed many animal body plans to evolve simultaneously, without leaving a trace of ancestry.
Counter-argument: This explanation is weak on many grounds. Firstly, it does not deal with the fact that there is nothing even remotely resembling Cambrian fauna prior to the Cambrian explosion. Even if all of the body plans could arise rapidly, it does not tell us from what they all could have come from. The record still indicates that much biodiversity came virtually out of no-where. Secondly, "Hox gene (regulatory-gene) mutations" can only re-arrange parts which are already there--they cannot create truly novel structures. An oversimplified discussion is that genes can be thought of in two categories: "master control genes" (Hox genes) and "body part genes." "Body part genes" code for actual body parts while "master control genes" tell those "body part genes" when and where to be expressed and create their respective part. However, Hox mutations will never create new "body part genes", and thus cannot add truly new phenotypic functions into the genome. The majority of evolutionary change must take place through evolving new "body part genes", which Hox mutations cannot do. This explanation cannot explain the order of biological diversity which appears in the Cambrian explosion. One reviewer in Nature notes these limitations:
"[H]omeobox genes are selector genes. They can do nothing if the genes regulated by them are not there. It is these genes that specify in detail the adaptive structure of the organs. To be sure, turning on a homeobox gene at the wrong place can result in the appearance of an ectopic organ, but only if the genes for that organ are present in the same individual. It is totally wrong to imply that an eye could be produced by a macromutation when no eye was ever present in the lineage before. Homeotic mutations that reshuffle parts do happen, and sometimes they may have led to fixation of real evolutionary novelties, but this does not mean that such changes are implied in the majority of speciations. In fact, macromutations of this sort are probably frequently maladaptive, in contrast to the vast number of past and present species-not to mention the fact that morphological differences between related species can be minute." (Book review of Sudden Origins: Fossils, Genes, and the Emergence of Species by Jeffrey H. Schwartz (Wiley: 1999). by Eors Szathmary in Nature 399:24, June 1999 pg. 745)
Finally, changes Hox genes appear to generally harm organisms more than being "miracle mutations" that can radically re-arrange body parts:
"The drawback for scientists is that nature's shrewd economy conceals enormous complexity. Researchers are finding evidence that the Hox genes and the non-Hox homeobox genes are not independent agents but members of vast genetic networks that connect hundreds, perhaps thousands, of other genes. Change one component, and myriad others will change as well--and not necessarily for the better. Thus dreams of tinkering with nature's toolbox to bring to life what scientists call a "hopeful monster"- such as a fish with feet--are likely to remain elusive." (Nash J.M., "Where Do Toes Come From?," Time, Vol. 146, No. 5, July 31, 1995. Also at "http://www.time.com/time/magazine/archive/1995/950731/950731.science.html")
Invoking mere Hox-Gene mutations to allow for "rapid evolution" during the Cambrian explosion ignores the extreme genetic complexities and phenotypic limitations inherent in manipulating Hox Genes.
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