Evolution hasn't been proved

Claim

Evolution has not been, and cannot be, proved.

Morris, Henry M., 1974. Scientific Creationism, Master Books, Arkansas, pp. 4-6.

While this claim is true as far as it goes, it doesn't go far enough. As it happens, no scientific theory whatsoever can be "proved"; this is because in science, you can never be 100% certain you you've identified all of the relevant axioms and principles. The best you can hope for is that a theory is well-supported by empirical evidence, and evolution is extremely well-supported.
Evolution cannot be proven, but it has been observed. When scientists took seeds of the plant, Nereis acuminata, and grew the seedlings (and their descendants) in three different environments (alpine, farmland, and coastal), they were unsuccessful in their attempts to cross them or their descendants, which is one of the many evidences for natural selection and evolution.
Evolution could be disproved. Many have attempted to disprove it; all of them have failed. This means that it is probably (even if not beyond all possible doubt) true.
The people who make this claim remain willfully ignorant of the thousands upon thousands of libraries' worth of evidence discovered in fossils, laboratories, and field observation.
That gene frequency changes with time can be, and has been, proven. That all organisms derive from a single common ancestor cannot conclusively be proven, but can be shown to not be in conflict with the facts. Short of a desire to invoke the supernatural, there is no reason to disbelieve it.
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Argument from Ignorance
Equivocation ("prove" is used in the mathematical sense in this claim)
Equivocation again ("evolution" can refer to either the fact of evolution or the theory of evolution)
Slothful Induction
Suppressed Evidence

Mark Isaak's page for this claim [1]
CreationWiki's comments [2]
Theobald, Douglas, 1999. 29+ Evidences for Macroevolution: The Scientific Case for the Theory of Common Descent with Gradual Modification [3]
Colby, Chris, 1993. Evidence for Evolution: An Eclectic Survey [4]
Moran, Laurence, 1993. Evolution is a Fact and a Theory [5]