Frequently, the debate over the validity of a subject distills down to the validity of the accepted evidence. There seem to be two lines of thought on this:

1) The only acceptable evidence is that which can be observed while occurring, and can be repeated.
2) When option 1 is limited or unavailable, or additional data is sought, we can provisionally accept less rigorous sources.

For example: We cannot directly observe the changes in star birth as the elemental mix of the universe has changed over time under the repeatable and controlled laboratory conditions described in option 1. We can, however, follow option 2, observing the past in a limited way, and drawing provisional theories from this evidence. We may refine these theories as more evidence is gathered, and as other fields of science mesh with our theory, perhaps developing a model utilizing physics predicting what we might additionally observe, and then finding the results to be true. We may even test parts of this theory under option 1 conditions to bolster our line of evidence.

We do not consider research into star birth invalid, simply because we cannot shoehorn the subject into the same category as simple chemistry. Like all theories, using either or both lines of evidence, our theory will be provisional, likely to be refined over time as new evidence arises.

As a theory ages, it becomes more robust when it more deeply meshes with other sciences. Though parts of the theory may be refuted, or refined, or not yet fully understood, the whole will stand until some competing theory explains the data with more precision and predictability. Proving that there are limits or shortcomings in a theory does not invalidate it, and certainly does not endow a different theory with automatic validation, as reality is not necessarily an either-or proposition.

In conclusion, both option 1 and option 2 are considered valid lines of evidence. Option 1 may carry more immediate weight than 2, but either may subsequently prove flawed or misunderstood, so either is still provisional, just as all scientific theories are. Even the theory of gravity, a force we do not fully comprehend, is provisional and subject to possible future amendment. The theory of evolution is no different in this respect, and both stand until better explanations arise.