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Science Frontiers ONLINE No. 109: Jan-Feb 1997 |
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Biology Heavy
Paleontology vs. DNA. The so-called Cambrian Explosion has been the subject of two SF items (SF#60/187 and SF#85/ 187). A paleontological fact of life is that all known body plans (phyla) seem to have evolved suddenly -- within a few million years -- after the onset of the Cambrian period some 545 million years ago. Evolutionists are understandably uncomfortable with such a high rate of evolutionary innovation. Nothing like the Cambrian Explosion appears in the hundreds of millions of years of geological strata that followed. So rapid was speciation during the Cambrian Explosion that doubt is cast upon the accepted mechanisms of evolution: slow, stepwise accumulation of mutations plus natural selection. (Refs. 1 and 2)
But G.A. Wray and colleagues seem to have rescued Darwinism. They have analyzed the DNA sequences of seven genes found in living animals. Assuming that these genes mutate at constant rates and working backwards in time, they calculate that animal diversification (i.e., when chordates diverged from invertebrates) actually began about 1 billion years ago, rather than about 545 million years ago. This expansion of the time frame gives accepted evolutionary processes much more time to innovate and create all those new body plans. The evolutionists are pleased.
The paleontologists, however, are in a quandry. They see nothing -- or very little -- in the Precambrian fossil record that substantiates the claim of Wray at al. Thus, molecular biology directly contradicts the findings of paleontology. Not to worry say supporters of the new and much more comfortable scenario: The Precambrian animals were so soft and "squishy" that they did not fossilize well. (Ref. 3)
Comment. The molecular biologists are a bit arrogant in their assertions. They seem to assume that because they can quantify molecular divergences; that is, fill their journal contributions with numbers; that their data is more sound than fossiliferous strata. But their crucial assumption of constant DNA divergence in time may be their undoing.
References
Ref. 1. Anonymous; "Deflating the Biological Big Bang," Science News, 150: 335, 1996.
Ref. 2. Perlman, David; "Origin of Animals -- 1.2 Billion Years Ago," San Francisco Chronicle, October 25, 1996. Cr. J. Covey.
Ref. 3. Wray, Gregory A., et al; "Molecular Evidence for Deep Precambrian Divergences among Metazoan Phyla," Science, 274:568, 1996.
Homology vs. DNA. Until the molecular biologists recently arrived on the scene, evolutionary family trees were based upon similarities in appearance; that is, homology. Animals that look alike must be closely related. But molecular biologists have discovered that some animals that seem identical to the eye differ significantly in their DNA complements.
Thus, the Pacific skinks may undermine homology. Inhabiting many, far-separated Pacific islands, these small lizards all look pretty much alike externally. For many years, biologists assumed that they all belonged to the same species. Recently, scalpels in hand, they found that the skink innards differed enough to define two species: Emioa cyanura and Emioa impar.
Next, the molecular biologists got into the act. They discovered that the mitochondrial DNA (mtDNA) of the Guam and Kosrae skinks differed by an amazing 6%, even though both skinks were E. cyanura. Even worse, the Vanuatu skink (E. impar) differed from all other E. impar skinks around the Pacific by an astounding 13%. Yet, to the eye, they all looked alike. So much for homology -- unless there is something basically wrong with molecular biology. Biologists now suspect that there are many more "cryptic species": animals that look alike but possess substantially different DNA complements.
(Cohen, Philip; "Lizards Keep Their Differences to Themselves," New Scientist, p. 17, July 6, 1996)
Comment. The flip side can be seen in humans and chimpanzees. From the standpoints of anatomy and behavior, these species are rather divergent; but their DNAs differ by only 2%! There is something suspicious in all this.
 | Three of the hundred or so basic body plans (phyla): jellyfish (Coelenterata), aphid (Arthopoda), eohippus (Chordata). The present fossil record indicates that all phyla appeared rather suddenly in early Cambrian times. |