rem, I just did a little reading on replicators and natural selection.
For the purpose of discussion, let's grant that, however improbable, there was indeed at least one self-replicator produced by an accident of purely physical processes. Scientific method requires that this step be reproducible if it is to be accepted as anything more than a speculation. So I found it interesting to read in Britannica (bold added):
It is possible for RNA to replicate itself by mechanisms related to those used by DNA, even though it has a single-stranded instead of a double-stranded structure. In early cells RNA is thought to have replicated itself in this way. However, all of the RNA in present-day cells is synthesized by special enzymes that construct a single-stranded RNA chain by using one strand of the DNA helix as a template.
This, together with your comment that "There are several different hypotheses about what these replicators could have looked like" suggests to me that this (apparently) essential step to the development of DNA is only conjectural. In that case, wouldn't I be compelled to go by what I can see, in terms of straight-forward demonstrable physics?
Also, as far as natural selection is concerned, it's important to distinguish between a descriptive principle and an explanatory theory. Identity and Reality (Emile Myerson, pp. 311-6) uses the example of Carnot's cycle:
Indeed, Carnot's principle is an empirical law, directly observable; it is the most general and most common of rules--it governs the totality of phenomena. This is far from being so for the variability of animals and vegetables; even admitting that this is an absolutely demonstrated fact, it is far from impressing itself upon our attention as much as the fact of the establishment of equilibrium of temperature. That is why it could not really become a part of science until an explanation of it had been found, or at least until a way had been indicated by which it seems possible to find an explanation. This was done, or at least attempted, by the initiators of the concept of evolution in biology--Lamarck, Darwin, Wallace. Did they succeed? Opinions differ on this subject, even amongst biologists.
Carnot's cycle is explained by Maxwell's theory, which provides the underlying (and apparently universal) physical principles that "drive" that cycle. In contrast, "natural selection" remains, in that respect, unexplained. (Myerson proceeds to illustrate how the lines between these two aspects of science often becomes blurred, as we can tend to 'read' teleological meaning into what we empirically observe in the world around us).
Which brings us back to the beginning:
Moreover, in supposing this reduction to mechanism carried to its very limit, it is evident that the primitive being, the source of all others, must in its turn be conceived as having evolved from inorganic matter. This conclusion may seem hazardous from the experimental point of view, since the results of micro-biological research tend to make us reject spontaneous generation; it constitutes, however, the necessary completion and crowning of the edifice, as eminent evolutionists have proclaimed it.
So, on the one hand I have no rational choice but to accept the clear empirical evidence of the cross-species similarity of DNA as evidence for the process of evolution. But on the other hand it doesn't provide me with an explanation for evolution, based exclusively on physical mechanisms.
Of course, my belief in a supernatural being directing these events doesn't explain anything either.