What would qualify as evidence for common ancestry or reproductive connection, I wonder. Just identical genomes for all of life? A single species of clones and nothing else?
See, this is why just accomodating data is not enough. “Explains the data better” is, as I recently explained in another thread, trivial at best, and vacuous at worst. A scientific model’s merits are measured by how well it predicts data, not by how well it can be constructed to match any. Separate ancestry is maybe consistent with just straight, unspecific “differences”, and common ancestry, without known mechanisms that would alter the genome between one generation and the next, is insufficient to explain them. The similarities are just the other way around, of course: Separate origins is not a sufficient account for why all life would have DNA-based genes at all, let alone why so much of it would be so similar between allegedly unrelated kinds, without unknown speculations about the capabilities or desires of magical beings in control of it all, while common ancestry perfectly accounts for why the thing that is being copied for the offspring ends up being indeed a copy of what was within the parent. So far so good.
But now the crucial part begins.
Given the experimentally verifiable fact that the copying process is not perfect, we (a) lose the expectation of the copies being perfect, and (b) we expect a hierarchical pattern of differences as lineages diverge. We do not see it first and then just make up an ad-hoc rationalization for why it makes sense. We expect to see this well in advance of actually checking. Finding that it is so makes plausible the conjecture that perhaps less than all of the reasoning we used to predict the observation is entirely off-base.
On the other hand, assuming separate origins we should expect patterns like these at best only within individual kinds, and, more importantly, we should expect groups of organisms that have entirely arbitrary things in common, if any at all. Animals that violate taxonomy should not be something we only find in fiction, but rather they should be the norm, because taxonomy should only work for the family of that one separate ancestor and be separate from the taxonomies of all the other kinds. Finding that all of life seems to neatly align within a single tree is consistent with separate origins only if some miraculous scheme to deceive us, or an outlandishly unlikely coincidence is invoked to account for the data, while the theory on its own cannot.
The data is in, Bill. In the rare instant where separate ancestry might make a prediction, its predictions conflict with the data unless excuses are involved. Predictions from common ancestry, meanwhile, do not, if observed facts are kept in mind. It’s not an open question.