Some posters here attempt to pretend that there really isn’t any evidence for evolution, that the theory merely arises from the “philosophical predisposition” of “atheist scientists”. (By “evolution” I here mean “common descent” and “descent with modification” and prescind from any particular mechanism.)
That is not to deny that such a predisposition exists. But opposition to evolution also arises from a philosophical predisposition, the desire to have the ancient beliefs of the Church and the Fathers proved correct, regardless of the evidence. I would like these posters to have the intellectual honesty to admit there simply is no evidence that could possibly convince them of evolution. Their m.o. simply consists of scanning the evidence for anything which could possibly be against evolution, while disregarding the totality of evidence. That is simply not how science is done. If their belief is that the argument to authority should always trump the argument to evidence, they should say so. I, for one, do not accept that principle. I think, however, that I have more or less “clean hands” here, meaning that I really do not adhere to the philosophical predispositions of either group.
It is admitted that complete objectivity is impossible in science. Inductive reasoning uses (or should use) Bayes’ theorem, which shows that the posterior probability of any particular model will depend on the prior probability, for which subjectivity simply cannot be avoided. Nevertheless it is possible to compare the likelihood of data under various models.
Now the piece of evidence which convinced me, once and for all, of the reality of evolution was the presence of endogenous retroviruses (ERVs) in the same location in the genome in all the major primate groups, including humans. An ERV is a virus which imbeds itself in the DNA (RNA-to-DNA is done using reverse transcriptase). Typically the virus then takes over the cell’s replication machinery until it dies. However, if something goes “wrong” in the process the DNA will enter the host DNA and stay there. Should this happen in a germline cell, and this be the gamete used for reproduction, this ERV copy will be passed on to the offspring. There are 12 or 13 of these ERVs which have been found so far (geneticists please correct if there are more) in the same location in the genome, and they follow the standard phylogeny among primates.
It can shown that this is strong evidence for common descent by comparing the likelihood of the data among the various models. If one species arose by common descent from another containing the ERV, the likelihood of the ERV being in the same place in the genome is close to one (not exactly one because a deletion event is possible). What if the species were specially created? If the second species were specially created without the ERV, then the ERV would have to become inserted in a germline cell in the exact same spot, and then this would have to become fixated in the population. The likelihood is vanishingly small. What if the second species were specially created with the ERV? We will assume then that the ERV would have some function, that the likelihood that a designer would just stick some random “junk” in the DNA with no function or a deleterious function is zero or close to zero. Now in fact some ERVs do have a useful function, for instance one ERV is associated with placental formation (syncytin). Other ERVs have a deleterious effect, being associated with cancer for instance. But, in syncytin formation, the entire ERV is not associated with syncytin. An ERV consists of three genes, env, gag, and pol, as well as a long-term repeat (LTR). But only the env gene is used for syncytin production. What’s the function of the rest of the ERV? Specifically, what’s the LTR (essentially “junk”), doing there? Why would a designer use specifically an ERV for this purpose? Why not just design an ordinary gene for syncytin?
Creationist responses in the past have typically included the following.
- Confusing the issue by citing ERVs not shared between primates, conveniently omitting the fact these are not in the same place in the genome, making the likelihood of independent insertions much greater.
- Confusing the issue by citing insertion hotspots; yes, insertion hotspots make certain regions more likely than others but insertion at the exact same location is still vanishingly unlikely in a genome with 3 billion base pairs.
- Confusing the issue by demanding an explanation for the differences in the genome, not just the similarities. This would be a valid point if the only options were “Biblical” creation versus atheistic, stochastic, undirected evolution. However they are not, and theories of front-loaded and/or directed evolution easily explain the similarities.
- Complaining that I am speculating on what a designer might or might not do. If a designer is brought into the equation, then it is necessary to do this in order to evaluate the evidence scientifically, which means evaluating likelihoods and applying Occam’s razor and parsimony. I can’t prove that angels don’t move the planets and stars around. But I can show their motion is accounted for by natural laws, which is a much more parsimonious explanation than angels, for the hypothesis space is much smaller. Why should angels be moving the planets in the exact same fashion as predicted by Kepler’s Laws, and later more accurately by general relativity? Similar considerations apply here.
Here is the AIG interpretation of retroviruses:
answersingenesis.org/articles/am/v1/n2/were-retroviruses-created-good which kind of just makes me want to say, get real.