Final answer:
The theory of evolution is called a theory because it is a scientifically supported explanation for the diversity of life, thoroughly tested and verified, with extensive evidence backing it, contrary to the misconception that it is 'just a guess' or an unproven concept.
Step-by-step explanation:
The term evolution is often called a theory because it has been extensively tested and supported by a vast body of evidence over time. This misunderstanding arises when critics purposefully confound the everyday usage of the word "theory" with its scientific meaning. In science, a theory is a comprehensive explanation of some aspect of the natural world that is supported by a vast body of evidence and has withstood rigorous testing and skepticism.
Examples include the theory of the atom, the theory of gravity, and the theory of relativity. Each of these theories, including the theory of evolution, describe what scientists understand to be facts about our world. Therefore, when critics say evolution is "just a theory," they are not acknowledging its rigorous scientific support and all of the evidence that substantiates it. The credibility of a scientific theory is not diminished when it is doubted or challenged; rather, this is a reflection of the evolving state of scientific knowledge.