Evolution is just a theory. This is true, except there is no "just" in "just a theory" when it comes to evolution or any scientific theory. There are only a few theories: evolution, gravity, atomic structure, electricity and magnetism, the duality of light. These are grand ideas, vast and elegant, that give structure to how we think about everything else.
Darwin set the course for more than a century of inquiry, and the experiments and studies used to test and explore evolutionary theory substantiated and proved his ideas.
In Darwin's time, little was known of cells. Darwin spoke vaguely of a "germ" passed from cell to cell and parent to offspring, because microscopes were too crude to allow better understanding. The periodic table was still under construction, and chemistry was too primitive to probe the molecules of life.
Before we could discover cellular reproduction and the genetic code, we first had to invent organic chemistry. Darwin knew little about the wondrous and diverse properties of elemental carbon. Proteins and ribosomes, the tools of evolution, were unknown to him. All these things were discovered because Darwin told us where to look.
Without his idea, medicine and science would be decades behind. Genetic crime-solving would not yet exist, and we might not know enough about hormones for athletes to abuse them or for doctors to use them beneficially. We would have a dimmer understanding of biodiversity and the ancient past.
Such is the beauty of a theory in science that once it is known its discovery seems inevitable, and if Darwin had not shared his insight, someone else would have. Alfred Wallace might have kept history on time, since he was sketching out similar ideas when Darwin completed his treatise. Wallace was an early champion of Darwin's theory and helped others understand it. He also refined the theory and built it a stronger mathematical framework.
Regardless of how we stumbled onto the idea of evolution, once it was here it dictated the course of a century of science, going on two. It's just a theory, and that's what theories do.
I am fond of another grand idea that has defined the course of history: the theory that we are imperfect and achieve salvation by loving and forgiving one another. It is not a scientific idea. You cannot set out to prove or disprove it, but you can discover that it is true. Darwin was also fond of this grand idea, and his theory evolved from it. Evolution is the idea that imperfection in reproduction enables a march toward perfection with each cycle of birth.
I know it is a myth that Earth was created in seven days, but I would not say it is "just" a myth. It is part of a profoundly important book and deserves only the highest meaning of the word "myth."
Often, ideas are bigger than the words we use to express them. We should be careful not to lose sight of big ideas by squabbling over words.
Hopefully, by now, the Farragut parent upset over the word "myth" in an honors biology text has withdrawn his complaint. A child smart enough to enroll in honors biology can hardly be sheltered from the facts that make evolution a theory and the Genesis creation story a myth. A single word in a chapter not assigned in the class is a laughably trivial battle in the war of ideas. If Kurt Zimmermann does not withdraw his complaint, the Knox County school board has to decide next week whether to ban a book, a non-trivial affront to American ideals. They will convene on Monday to discuss their agenda and Wednesday to vote.
Evolution is too simple and beautiful an idea to deserve the kind of resistance it gets from fundamentalists. It is not just a theory; it is everything in that honors biology text. Fundamentalists already lost the war of ideas, and pointless school-board skirmishes debase everyone involved.