When you say, "The theory of evolution is something that can never be proven or disproven definitively," that's actually incorrect. The theory of evolution CAN be disproven. And that's the beauty of it.
There are lots of ways to disprove evolution. The classic example is the; that is, a fossil whose geologic history is incompatible with biological history. Such a thing would, definitively, disprove evolution. It's just one of many ways to disprove evolution.
It's precisely because evolution can be disproven that makes it, or any other scientific theory, valuable. Theories that can't be disproven are of zero utility. They serve only for warm fuzzies, and while those warm fuzzies appear to be of intense interest to the vast majority of people wringing their hands about evolution, they're of no interest whatsoever to people who actually want to achieve things in the world: developing medicines, decoding the genome, even finding oil and predicting earthquakes.
The fundamental value of science is when you take a bunch of known facts, run them through your theory to derive a thing which had been unknown, and then rely on it if as if you knew it to be true all along. If the theory were false, that thing would turn out not to be true, and you'd fail in your endeavor. But when the theory is true, that new fact also turns out to be true. A theory that can't be disproven can't distinguish between correct and incorrect answers, and so it doesn't make any difference. It leads nowhere.
Not every science leads directly to applications, but all scientific processes fundamentally come down to that process. The various scientific disciplines, including the purely theoretical ones, all bolster one another to build up an edifice that allows us to extrapolate from things we know to things we don't yet know but can rely on.
The important thing about evolution is that unlike competing notions of life on earth, it is the only one which COULD be proven false, and is therefore the only one worth anything at all. Even if evolution were proven false, the other ideas (it's invalid to call it a theory, for this reason) would remain utterly worthless.
People remain attached to them because they are not scientists and never build things of value from the tools that science gives us. They enjoy only the special feeling they get from being distinct from non-human animals. If you want a special feeling, get a dog. If you like to accomplish things, you study science. And that study will provide so many examples of places where the theory evolution could have been wrong, but wasn't.
More questions on Evolutionary Biology:
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