Evolution 101

Thursday, May 04, 2006

Molecular Evidence 6: Objections to Molecular Evidence

All right, this is the final podcast in a series of six that I’ve planned on the molecular evidence for evolution. I’ve been using Dr. Douglas Theobald’s resource on Talk.Origins.org pretty heavily, so you can use that to follow along with the previous five episodes if you like.

To get to this point, I’ve introduced you to the basics of molecular biology, I’ve explained why function follows from structure, why structure follows from sequence, and why sequences are functionally redundant, both with amino acids and with nucleic acids. I’ve shown you sequence homology between different species, verifying the evolutionary hypothesis. I’ve also taken you through noncoding DNA sequences, analyzing three different kinds of molecular artifacts which also verify the evolutionary hypothesis. Every last bit of genetic information that’s contained in your genome indicates that you share a common ancestor with chimpanzees and other primates, by any conceivable measurement.

Genetic information has an advantage over other kinds of evidence, such as fossils. Fossils are the result of genes that existed in the past, but the genetic information we analyze in living organisms is very much a part of the here and now. It’s a living, breathing (literally) piece of evidence. We can measure it, find out how it works. If you compare the fossils of two different kinds of dinosaurs, for example, which both have the same kinds of foot structure, we can hypothesize that they were related phylogenetically, but that’s all we can do. If we were to take two different kinds of organisms today, we can do the same thing, but we can go one step further- we can compare their DNA. Every physical structure that exists as a part of their body is the result of their particular genes- their genotype. The physical manifestation of that genotype is called a phenotype. So, a gene which codes for a protein which regulates beak shape in a bird is part of its genotype, and the shape of the beak is the phenotype. For living organisms, we can correlate genotype with phenotype, and since heredity is the only known mechanism for shared genotype, it’s so much more powerful than just comparing the way animals look.

Despite the power of genetic evidence, there are still detractors, people who don’t accept the conclusion that the molecular evidence supports the evolutionary hypothesis. This is just one of those things that happens in Science- not everybody is going to accept your conclusions. That’s okay, and it happens with just about everything. There are people who don’t accept the HIV hypothesis of AIDS- they don’t believe that the Human Immunodeficiency virus is what causes AIDS. There are also people that don’t accept the cholesterol hypothesis of cardiovascular disease- they think that you can eat as much cholesterol as you want and you won’t get a heart attack. Some of these criticisms come from scientists- the scientific community in general isn’t monolithic and dogmatic, at least it’s not supposed to be. There are always conflicting hypotheses in Science, and it often takes a long time before there’s sufficient experimental evidence to show that one hypothesis is right and the other is wrong. Whatever the case, when the evidence piles up, scientists generally all get behind the hypothesis that the evidence supports, and the conclusion is, for all practical purposes, a closed issue.

This is the case for evolution. The evidence supporting evolutionary theory has been piling up for a couple centuries now, and it’s basically a closed issue in the scientific community. It’s like the HIV hypothesis of AIDS or the cholesterol hypothesis of cardiovascular disease- there’s just no debate among scientists; the evidence is overwhelming.

The reason why I’m making this point is because I want to make it clear that the objections raised against evolutionary theory don’t come from scientists. They come from people with an ideological and theological presupposition that demands a rejection of evolution- of course, I’m talking about creationists. If you have noticed, there’s a critique of Dr. Theobald’s reference at Talk.Origins that is written not by another scientist, but by a lawyer, named Ashby Camp. Why would a lawyer be interested in critiquing scientific evidence for evolution? Well, it just so happens that Mr. Camp is not just a lawyer, he’s a Church of Christ minister and avowed creationist who wrote his critique for the website TrueOrigin.org, which is subtitled, “exposing the myth of evolution.” Clearly, Mr. Camp has a theological interest in portraying evolution as false- he views evolutionary theory as incompatible with his own theology, and therefore must choose one or the other. Obviously, he’s chosen to assert his theology- but this is not always the case. Dr. Kenneth Miller is an evolutionary biologist who finds the science of evolutionary theory compatible with theology, and he writes about this in his book, “Finding Darwin’s God,” which I can recommend highly as a popular introduction to evolutionary theory, especially for those who are under the same assumptions as Mr. Camp.

Since arguments against scientific theories from theology can’t offer competing scientific evidence, they almost always employ a type of argument commonly referred to as an “argument from ignorance.” These are very attractive, but are also logically fallacious. They’re easy to spot, too- all you have to do is listen or watch for someone to start talking about something that Science “doesn’t know,” or talk about something which “may be possible,” even though there’s no evidence to support the conclusion now. The implication is that since something is not known to be the case, it is not the case, or vice versa. Since these arguments against Science often come from a theological perspective, they’re also known as “God of the Gaps” arguments, because the idea is that there is some gap in scientific knowledge that is explained only by assuming that a deity is responsible for that phenomenon. Coming from a theological perspective makes these kinds of arguments no less fallacious, however, and if you run across any kind of criticism of this sort, be sure to pay attention for the arguments from ignorance, or the “God of the Gaps.”

This kind of argument is precisely what we see from Ashby Camp. When confronted with the evidence from protein functional redundancy, he says, “how could one be sure that God would not conserve amino acid sequences (or the underlying codons) when creating cytochrome c in separate species? After creating cytochrome c in the first organism, it certainly is conceivable that he would make changes to that blueprint only when necessary for his purpose. In other words, the default in this instance may be similarity rather than dissimilarity. There is no basis for demanding that God introduce novelty for novelty’s sake.” In other words, since we don’t know that God did not create cytochrome c functionally redundant in different species, he must have done so. Did you catch the argument from ignorance? When confronting the evidence from DNA functional redundancy, he says basically the same thing, “how could one be sure that God would not conserve codon sequences when creating cytochrome c gene in separate species? After creating the cytochrome c gene in the first organism, it certainly is conceivable that he would make changes to that blueprint only when necessary for his purpose. In other words, the default in this instance may be similarity rather than dissimilarity. Again, there is no basis for demanding that God introduce novelty for novelty’s sake.” Same argument from ignorance, and it’s just as fallacious the second time around.

The same mistake is repeated for the rest of the evidences. Regarding transposon, he says, “God may have had a functional reason for initially placing them at the same chromosomal location in separately created species. He also may have had a functional reason for designing certain transposons with an insertion bias for certain loci.” Regarding redundant pseudogenes, he says, “maybe lateral gene transfers occurred in the past through a mechanism that targeted a specific location in recipient cell DNA and that did not leave viral sequences near the inserted pseudogenes. Perhaps this mechanism is no longer operating, as a result progressive degeneration, and the viral action we see today is a distorted remnant of that originally designed process.” Regarding endogenous retroviruses, he says, “God may have had a functional reason for initially placing them at the same chromosomal location in separately created species. He also may have had a functional reason for designing a system to favor the insertion of certain ERV sequences at certain loci.” Did you catch all those “maybes” and “perhaps?” That’s right, obvious giveaways that he’s arguing from ignorance.

And it’s also the special case of the argument from ignorance, the God of the Gaps. For every piece of evidence, Mr. Camp makes the statement, “God may have a purpose for doing so that is beyond our present understanding.” In other words, Mr. Camp is making the claim that there is some kind of gap in our scientific knowledge about molecular biology in which some yet unknown purpose may have been intended by God.

This should be pretty easy for you now. When it comes to criticisms of the evidence for evolution, keep your ears open for arguments from ignorance, and that special case, the God of the Gaps. If you do that, it should be pretty easy for you to shut down critics who use logical fallacies as their only weapons. Well, this is it for the Molecular Evidence for Evolution. I hope this has been interesting and instructive, and more than that, I hope I’ve motivated some of you to check out the evidence for yourselves. Next week, I’ll be back to answering questions. Take care.


Post a Comment

<< Home