I'm having a problem with the fact that you're arguing less like a scientist and more like a lawyer trying to get an axe murderer off the hook on a technicality.
Your quote, emphasis mine:
"On the other hand, you CAN disprove a theory by finding even a single observation that disagrees with the predictions of the theory."
Note that the above does not say any
single observation will
disprove a theory, and it says nothing about to what degree
the theory might be disproven. For the sake of being concise, the statement quoted above is dealing with a notion of "theory" which is more like a simple proposition, something without the complexity and scope that many real-world theories possess.
For example, there's a single observation that one could say falsified Newton's theory of gravity: small anomalies that were discovered in the orbit of Mercury, showing an orbit for Mercury which didn't quite match the orbit expected following Newton's equations.
Newton's gravity was open to falsification. A single falsifying observation was found. Newton's gravity was falsified. End of story?
Of course not. If you quote too blindly from a very dry definition like the one above you might think so, but then you'd never be able to appreciate the fact that, although technically invalidated, Newton's gravity is still more than good enough for most practical uses, even good enough for a lot of work in astronomy
, because only speeds approaching the speed of light and strong gravitational fields introduce significant differences in predicted results.
Like Newton's gravity, evolution has served so well for so long with such a large body of collaborative data backing it up, it's quite understandable and thoroughly justifiable
to suppose that even if a well-confirmed observation technically falsified the theory, the end result of accounting for that observation would be more like Einstein's gravity supplanting Newton's than it would be like, say, the Copernican solar system replacing Ptolemy's crystalline spheres.
If one were a young earth creationist, one certainly shouldn't be holding one's breath waiting for evolution to be so thoroughly discredited by conflicting observations that somehow something like young earth creationism actually rises to the status of being a better
explanation. A battle between a hypothetically broken-down evolution and young earth creationism would simply be a battle to decide which one was bad, and which one was worse. Scientists would be thrown back to having no good theory at all, and would have to go back to square one to figure it all out again.