|Evolution in the News - March 1998|
Biologists aren't entirely satisfied with the intrinsic subjectivity of classification, and have hoped that molecular biology would yield a more quantitative approach. It was hoped that comparisons of the nucleotides of DNA or RNA sequences would yield quantitative numbers that could be used to classify organisms with a high degree of accuracy. According to an article in the January 1998 issue of Science,
|Animal relationships derived from these new molecular data sometimes are very different from those implied by older, classical evaluations of morphology. Reconciling these differences is a central challenge for evolutionary biologists at present. Growing evidence suggests that phylogenies of animal phyla constructed by the analysis of 18S rRNA sequences may not be as accurate as originally thought.1|
The article then discusses a figure that shows that mollusks are more closely related to deuterostomes than arthropods when the creatures being compared are a scallop (a mollosk), a sea urchin (a deuterostome), and a brine shrimp (an arthropod). That isn't too surprising. Intuitively, a scallop seems more like a sea urchin than a shrimp, and the 82% correlation between the scallop and sea urchin shown on their diagram isn't surprising.
But when a tarantula is used as the representative of the arthropod, there is a 92% correlation between the scallop and the tarantula. It doesn't seem reasonable that a scallop should be more closely related to a harry, land-dwelling spider than to a sea urchin. This is troubling to the authors of the Science article, which leads them to remark,
|The critical question is whether current models of 18S rRNA evolution are sufficiently accurate current models of DNA substitution usually fit the data poorly.2 [emphasis supplied]|
It is more than slightly ironic that the article was titled, "The Coming of Age of Molecular Systematics." The text of the article says, in effect, that molecular systematics is still in its infancy, doesn't provide any useful information yet, and more work needs to be done. (Guess who might be seeking a grant to do that work. )
As the author of more than 50 articles published in several different well-known computer magazines, I know that very few of those articles were published with the title I gave to the article. Magazine editors sometimes feel they can make an article more appealing (and sell more magazines) by "punching up" the title a little bit. It is quite possible that the authors really titled their article, something like "Problems and Inconsistencies in Molecular Systematics", and an editor chose to "improve" it.
Since the authors are evolutionists, it never occurs to them that the data doesn't agree with the assumed evolutionary relationship because the theory of evolution is wrong. They fall back to the old "evolution happened so fast we must have missed it" argument. They assume a "rapid divergence of most of the animal phyla" that caused not only missing link fossils, but also missing link RNA sequences.
|Given the probable rapid divergence of most of the animal phyla, the complexities of 18S rRNA sequence evolution, and the problem of taxon sampling, it is difficult to have confidence in 18S rRNA trees in the absence of corroborating evidence.3|
In other words, if the results agree with what the theory of evolution (the Mother of All Corroboration) predicts, then the results of the RNA analysis are right. If they don't, they are wrong. They may find 99 sequences that don't show the assumed evolutionary relationship, but if they find one that does, that sequence will be "independent proof" that the traditional classification was correct. So, the RNA method is just as subjective as old-fashioned classification by physical characteristics.
In related news, an article in Discover magazine began with this paragraph:
|At some point during the growth of an insect larva, a gene called Dll switches on and helps organize some of its cells into legs. If for some reason Dll is shut off, the insect will produce only stumps. In the early 1990s scientists were surprised to discover that almost identical copies of this gene can be found in mammals and other vertebrates--and that they too switch on as legs form. This was surprising for two reasons. For one thing, insects and vertebrates have radically different limbs: ours have bone inside and muscle outside, while bugs are the reverse--their flesh is protected by an armored exoskeleton. For another thing, insects and vertebrates are only distantly related: our last common ancestor lived perhaps a billion years ago and was assumed to be limbless, like a flatworm. Researchers therefore imagined the two lineages evolved their limbs--and the genes that build them--independently.4|
The key word in that last sentence is "imagined."
The article doesn't state the problem very well, so it is easy to miss. It is miraculous that a flatworm would evolve into a primitive insect which, through chance and natural selection, happened to produce the Dll gene which was inherited by all subsequent insects. It is a double miracle if some primitive fish happened to, by random mutation, produce exactly the same Dll gene which turned it into the first amphibian that passed the gene along to all subsequent amphibians, reptiles, and mammals.
The disturbing news (to evolutionists) is that they've found this same gene in shellfish, too. So, the same miracle had to happen three times. There's got to be a limit to the number of times you can wave this magic wand!
The alternative explanation is that the mythical, legless, ancestral flatworm already had this gene, but it didn't do anything. It just happened to be there to help all the other future genes build a wide variety of legs. That takes a lot of faith, and brings another problem with it.
If Dll has been around for a billion years, why hasn't it mutated? The "mitochondrial clock" was formerly believed to experience one mutation every 600 generations. But studies on the descendants of the last Russian tsar, Nicholas II, show one mutation every 40 generations.5 (This causes some problems for evolutionists because, "Using the new [mitochondrial] clock, she [Mitochondrial Eve] would be a mere 6,000 years old."6 But that's another story.)
Granted, the mutation rate for human mitochondria might be slightly different from insect genes, but Dll should have mutated at least a little bit after a billion years.
The more we know about genes, the more trouble it causes for the
theory of evolution.
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Maley & Marshall, "The Coming of Age of Molecular Systematics,
Science, 23 January 1998, page 505
3 Ibid. page 506
4 "Hidden Unity", Discover, January 1998, page 46 (Ev)
5 Ann Gibbons, "Calibrating the Mitochondrial Clock", Science, 2 January 1998, page 28 (Ev)
6 Ibid. page 29