It's a tired old routine, yet time and again the same argument is taken off the shelf, dusted, buffed and then presented with a sly smile as if it were something new. Evolution, it's asserted, is only progressive and builds on earlier adaptations in its march forward through natural history. Therefore, if there is any evidence that a species adapted "backwards" it must mean that natural selection is flawed. However, the fallacy in this argument is that natural selection has nothing to do with progress, it's merely one of the mechanisms by which species successfully adapt to their environment. Genetic mutations don't have a direction in mind when there's a mistake in transcription or as a cosmic ray collides with a nucleotide of cytosine. If the organism succeeds once this genetic alteration occurs, they'll reproduce and spread the mutation further. It says nothing about a march of progress.
Those who oppose evolution without bothering to first understand it have repeatedly hailed this fallacy as a triumph. It was the centerpiece of the laughably bad polemic Icons of Evolution by intelligent design advocate Jonathan Wells (a detailed review can be found here). Now the same sickly horse has again been prodded out to market despite how often such duplicity has been exposed in the past.
In the journal Current Biology (subscription required), Richard Borowsky found that blind cave fish whose genes for vision have mutated over the course of evolutionary history could have their vision returned by interbreeding with other blind cave fish with differently mutated genomes.
According to the review in Science Daily:
The study examined four populations of blind cave fish, Astyanax mexicanus, which inhabit different caves in northeast Mexico. Blind for millennia, these fish evolved from eyed, surface fish. The researchers' genetic analysis showed that the evolutionary impairment of eye development, as well as the loss of pigmentation and other cave-related changes, resulted from mutations at multiple gene sites.
In order to gauge how genetic make-up could bring about the restoration of vision, the researchers created hybrids of the different cave fish populations. Among these various hybrids, they found that nearly 40 percent in some hybrid crosses could see.
Fascinating stuff. These results support the view that different species each adapt to their environment in unique ways, precisely as evolutionary theory predicts. However, the results must have been a little too uncomfortable for intelligent design creationists because immediately both Uncommon Descent and Creation Ministries International (which produces the young Earth themed Journal of Creation) hit upon the news as evidence that evolution must be wrong. Dr. Carl Wieland, writing for Creation Ministries, objects to this evidence of multiple evolutionary trajectories and insists that:
It would not take long at all, once a group of fish are cut off from the daylight by some geological circumstance, for an eye-losing mutation to be established by natural selection as described.
Of course, if Dr. Wieland had bothered to read the actual article (rather than merely the press reports that creationists are so fond of) he would have found that Astayanax mexicanus "evolved from eyed, surface-dwelling forms which only reached the area in the mid-Pleistocene," that is, between 600,000 to 1 million years ago. How does Borowsky know this? This is where references matter.
Earlier research by Ulrike Strecker and colleagues, published in Molecular Phylogenetics and Evolution (subscription required) showed that mutations occur in freshwater fish at a rate of 1.5% per million years. By analyzing the differences in cytochrome b genes between currently living species and then dating the nearest common ancestor of each in the fossil record, Strecher et al. proposed that Astyanax first arrived in the Yucatan no earlier than 900,000 years ago, just as Borowsky states. How can Wieland be so certain that "it would not take long at all" for such mutations to occur? Not presenting any evidence to back up his assertion we can only wonder how he determined this. But then, already walking down a blind alley, Wieland goes on to make matters even worse by asserting that:
Cave fish have arisen by processes that in fact demonstrate the opposite [of natural selection]--deterioration of function, consistent with the 'natural' direction of genetic change in a fallen world.
Here the good spin-doctor rests on the fallacy that has failed so miserably for so long: if evolution is about building up then mutations that result in deterioration must prove evolution is false. But even more than this, the fact that these cave fish have lost their vision supports Dr. Wieland's contention that the sin of man has affected all of creation. If you're a little confused then you're in good company. Apparently Wieland (and other Young Earth Creationists in general) think that Adam and Eve's violation of God's dictates resulted in the beginning of genetic change. Prior to the "fall" there was no aging, no genetic deterioration and no death. Far from revealing additional evidence to the already weighty tome of evolutionary theory Wieland instead sees evidence of God's divine plan. And Creationists accuse scientists of imposing their views on nature? Of course, why God in his infinite wisdom would feel it necessary to put out the eyes of a few Mexican fish to punish humans for their hubris is anyone's guess. But I suppose that's why it's called blind faith.
References:
BOROWSKY, R. (2008). Restoring sight in blind cavefish Current Biology, 18 (1) DOI: 10.1016/j.cub.2007.11.023
Strecker, U., Faundez, V.H. and Wilkens, H. (2004). Phylogeography of surface and cave Astyanax (Teleostei) from Central and North America based on cytochrome b sequence data. Molecular Phylogenetics and Evolution 33(2): 469-481. doi:10.1016/j.ympev.2004.07.001
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As one of those creationists folks myself, and one without a degree in Evolutionary Anthropology or anything similar, I'm not going to try to argue the topic with a scientist like yourself.
However, I will freely admit that there's some illogical spin often produced by my side of the debate. The assertion, for example, that the selection of cave fish disproves natural selection is ridiculous--quite the contrary, as you point out, the selection of blind cave fish by natural selection in the caves provides evidence that natural selection does indeed produce change in populations. No doubt about that.
And there is no doubt that Creationist "science" is so driven by trying to prove the creationist viewpoint that it is more of an apologetic argumentation than actual science.
But I think the reason there is so much debate about the significance of this find is because the word "evolution" is being used in a fuzzy way. While it is true that these finds confirm "evolution" if we are using the term evolution to refer to genetic change caused by natural selection, what this find fails to do is show any real confirmation of the argument that natural selection is able to build more complex creatures from simpler ones.
What the creationists are asserting, regardless of whether their terminology is correct, is that this find, far from supporting the contention that more complex creatures can be produced by natural selection, seems to indicate the opposite.
Thanks for the thoughtful reply Mitchell. However, the problem lies not with evolution but in popular misunderstandings of evolution. Natural selection isn't just about building complexity. It's primarily about adapting to local conditions. Genetic mutations can generate new phenotypes that promote complexity in populations and at other times reduce complexity depending on the circumstances. In this case it would seem that the energy saved by not producing functioning eyes in an environment where they would be useless was adaptive. This is not "moving backwards," as some have said, it is always about what works in the current environment.
Love that picture! Since Darwin died an old man I guess we know who kicked whose ass. Go Darwin! Where Mitchell and creationists fail is to see all these finds as a continuum of amazing development of life through the long long ages.
Back in the 1960's when I took population genetics, I learned that loss of a function, as a result of no selection for maintaining that function, was the ________ effect. I cannot remember the person's name and it has bugged me for years. Loss of sight in cave-dwelling animals is an example of the __________ effect.
One wonders if the other sensory systems: taste and smell, as well as lateral line system, and the associated brain processing centers, would be more complex in the blind cave fish than in their sighted conspecifics.
Do you mean the loss-of-function effect? Muller referred to this as an amorphic mutation, or null gene, because it interrupted translation or transcription of a gene that had been functional.