The definition evolutionist work with is using a religious style definition of a tautology. When I ask someone to define what evolution is they define the principles of genetic mutation, survival of fittest, etc. When I get deeper into the explanation of how the principles explain reality, the variation, rapid change, etc, there are large gaping unknowns and the some principles, while completely unproven, are thrown in as placeholders with no meaning and no evidence.
The big bucket of evolutionary principles has been shaken many times and ideas have been thrown out because of evidence. If what what defines evolution can't change and can't be disproved because they say, "oh, we really meant that,[see look...we need more money]." Then it is absolutely not like the law of gravity. If rocks started falling up the law of gravity would be completely thrown out. The definition of gravity is things attract by mass and if things don't, then gravity can't be true. There must be some other undiscovered force and what was once gravity will be redefined as the new force.
Evolutionist claim evolution is the answer to biological origins. However, every question asked about biological origins has an answer of Evolution. If you already define evolution to be the answer to the question, then it doesn't answer the question.
Some evolutionary principles are answers to what we see of reality and we must fully accept; however, you can't make the claim that evolution is true because it has no meaning and doesn't stand because, as a concept, if its ties to reality continually change then evolution is a process of discovery and not a conclusion that can be true.
(I know this is how math works.) If evolutionary theory is just any answer that is the opposite of a god (ID) made us, then you are defining it as the negation of a null statement. Then there is no evolutionary theory because the negation of null is still null.