Atlanta ? A trial opened Monday over whether a warning sticker in suburban Atlanta biology textbooks that says evolution is “a theory, not a fact” violates the separation of church and state by promoting religion.

The case is one of several battles that have been waged in recent years in the Bible Belt over what role evolution should play in science books.

It’s a battle that’s familiar in Kansas. In 1999 the Kansas State Board of Education made teaching evolution optional, but the board reversed that decision in 2001.

Cobb County, Ga., schools put the disclaimers in biology texts two years ago after more than 2,000 parents complained the books presented evolution as fact without mentioning rival ideas about the origin of life, namely creationism.

A group of parents and the American Civil Liberties Union then filed a lawsuit over the stickers.

“It’s like saying everything that follows this sticker isn’t true,” said Jeffrey Selman, a parent who filed the lawsuit.

The sticker reads: “This textbook contains material on evolution. Evolution is a theory, not a fact, regarding the origin of living things. This material should be approached with an open mind, studied carefully and critically considered.”

A lawyer for the school district, Linwood Gunn, said the sticker was meant to “encourage critical thinking” and said it did not imply that evolution was wrong. Gunn said it was silly to consider the stickers a promotion of religion.

“It doesn’t say anything about faith. It doesn’t say anything about religion,” he said.

But U.S. District Judge Clarence Cooper asked Gunn why it was necessary to have a sticker clarify evolution as a theory: “Why put a sticker on the book when that’s already in the book?”

Gunn replied that school board members were simply trying to accommodate all views.

The first witness, parent Marjorie Rogers, started the drive to put the stickers in the books. She said it was only fair to put a small disclaimer in a textbook where religious-based ideas about the origin of life were not mentioned.

“I don’t want the Bible taught in the classroom. But there is a wealth of science that would support intelligent design, and that is not taught,” she said. “There should be a marketplace of ideas.”

The judge also heard from a science teacher who said some students pointed to the sticker and argued evolution was “just a theory.”

The sticker “diminishes the status of evolution among all other theories,” teacher Wes McCoy said. “I was worried. I didn’t want college admission counselors thinking less of their science educations, thinking they hadn’t been taught evolution or something.”

The U.S. Supreme Court ruled in 1987 that creationism was a religious belief that could not be taught in public schools along with evolution.

The theory of evolution says evidence shows current species of life evolved over time from earlier forms and that natural selection determines which species survive. Creationism credits the origin of species to God.

The trial, which will be decided by the judge, is expected to last several days.