A few people have notified me to let me know that front-loading is being discussed on UD by someone with the moniker ‘genomicus.’ In one place, genomicus states that cytosine deamination is a prediction of front-loading. Someone else with the moniker “eigenstate” disagrees and writes:
The fail point here in this item is “so why would a front-loader choose cytosine as a base in DNA?”. It’s not sufficient to offer us *a* reason why you think cytosine would be chosen (and this is particularly devastating if you are offering this putative prediction in the context of an “intelligent design” explanation, an explanation with an unknown, inscrutable, mysterious designer). The choice must follow NECESSARILY from the hypothesis.
You are quite conspicuously working backwards from your conclusion. Coming up with a plausible choice — and given an unspecified, unknown, potentially omniscient and omnipotent designer, ALL choices are plausible — does not ground a prediction. First you lay out the hypothesis, the proposed mechanism, and then you deduce from that NECESSARY implications that proceed from that. If you can affirm what is entailed from your model, you got something! Sometimes those predictions are trivial or banal, and so don’t carry much weight. Other times they just don’t distinguish the hypothesis from other, competing hypotheses. But in this case, if you COULD establish that such a choice was ENTAILED from your proposed model, that would be quite substantial, indeed, I think.
I would not agree with genomicus that front-loading predicts the cytosine deamination story. That whole story is more subtle and complex than that. Let me explain.
In 2001, Poole, Penny, and Sjoberg published a paper in Nat Rev Mol Cell Biol entitled, “Confounded cytosine! Tinkering and the evolution of DNA.” In the abstract of this paper, they make the following assertion: “Early in the history of DNA, thymine replaced uracil, thus solving a short-term problem for storing genetic information-mutation of cytosine to uracil through deamination. Any engineer would have replaced cytosine, but evolution is a tinkerer not an engineer.”
Is it really true that “any engineer would have replaced cytosine? Poole, Penny, and Sjoberg are effectively arguing that because of its propensity to mutate through deamination, there is no rational reason for using cytosine as a base and it exists only as a “frozen accident.” In other words, this aspect of cytosine is being used, at least in part, as an anti-design argument.
What I did is to draw from a teleological perspective to make a prediction. The prediction was simply this: Given its propensity to being damaged, there must be a reason cytosine was included as one of the four bases of DNA/RNA. This prediction is entailed by the teleological hypothesis that life is ultimately rational; if life was designed, then there is a reason behind its architecture and composition.*
So it’s not that front-loading predicts cytosine would be used as a base. It’s that a hypothesis of life’s design predicts there would be a reason cytosine was used as a base.
This prediction then provided the impetus to take a closer look at the relationship between the genetic code and cytosine deamination. And as a result, I uncovered a pattern that no one else (AFAIK) has seen – a reason to include cytosine as a base. A copy of my original description is posted here and I provide a more polished account in my book.
Let me summarize. I don’t think front-loading predicts cytosine would be incorporated into the DNA. I predicted that there would be a reason for including cytosine, and its propensity to deaminate, in response to Poole et al.’s assertion that “Any engineer would have replaced cytosine.” That assertion has been refuted. They asserted that no engineer would have used cytosine as part of the genetic material because of its predisposition for deamination. But it’s exactly this predisposition that might cause an engineer of evolution to include it.
*It is worth noting that non-teleologists, as a whole, agree with this logic. For example, when they (and I) cite useless junk DNA as an argument against design, they (and I) are drawing from this logic.