Sorry, Donuel, "the theory of evolution" has not been investigated by experiment. (reason for the quotes, later)
The meaning of the word "theory" is an attempt at a systematic, rational basis for understanding some phenomenon. Note the word "attempt". Thus, "the theory of mathematics", "the theory of tort law", "the theory of gravity", and so on. Along with the rest of science, such theories are always looked at as works in progress.
Evolution is an observed fact. Various species can, in retrospect, be observed to have changed over long periods of time. Equally, new species have emerged over time. The theory of it is an attempt at having a systematic understanding of what has been observed, and the process behind it. The particulars of evolution can only be observed in hindsight, and cannot be subjected to experimental test, despite what I suppose are millions of generations of fruitflies and flatworms and other such extremely short-lived species studied in the laboratory. As to origin of species, despite a lot of studies, a lot of inbreeding and cross-breeding and exposure to mutagens of various animals, large and small, science has never been able to create a new species (so far, at least). Strange variations, yes, but species, no. So the word "experiment" is a misnomer in this connection.
Now (as promised) the reason I put quotes around "the theory of evolution": There are many theories of evolution, the best known and to most minds the most convincing of which is that of Darwin. I suppose it would be possible to concoct some sort of intelligent design theory of evolution, too, but of course those who use those words usually aren't into rational explanation. Certainly I have never heard of any theoretical system of evolution by intelligent design being put forward. "Intelligent design" in relation to evolution, or cosmology, or whatever else, is (in my experience, at least) an exercise in obscurantism.