Harrisburg, Pa. ? The latest chapter in a long-running debate over teaching evolution in public schools is about to unfold in federal court. In a civil trial set to begin Monday, the Dover Area School District in Harrisburg, Pa., will defend its policy requiring ninth-grade students to hear about “intelligent design” in a preamble to biology lessons on evolution.

Intelligent design, a concept advanced over the past 15 years, holds that Charles Darwin’s theory of natural selection causing gradual changes over time cannot fully explain the origin of life or the emergence of highly complex life forms. It implies that life on earth was the product of an unidentified intelligent force.

Critics say intelligent design is merely creationism – a literal reading of the Bible’s story of creation – camouflaged in scientific language, and it does not belong in a science curriculum. Eight Dover families are suing the school district, alleging that the policy violates the constitutional separation of church and state.

“Our objective is to demonstrate that the prior (legal) precedent, which forbids the teaching of creationism, applies here as well,” said Eric Rothschild, a Philadelphia attorney representing the families.

The state American Civil Liberties Union and Americans United for Separation of Church and State are assisting the parents, including lead plaintiff Tammy Kitzmiller.

Clarence Darrow, left, and William Jennings Bryan sit beside each other at the Scopes Monkey Trial in Dayton, Tenn., in this 1925 file photo. Darrow was one of three lawyers sent to Dayton by the American Civil Liberties Union to defend John T. Scopes, a biology teacher, in his test of Tennessee's law banning the teaching of evolution. Bryan testified for the prosecution as a Bible expert.

“The school board has no business instructing children about religious matters,” Kitzmiller said at a December news conference on the lawsuit.

The history of evolution litigation dates back to the famous 1925 Scopes Monkey Trial, in which Tennessee biology teacher John T. Scopes was fined $100 for violating a state law that forbade teaching evolution. The Tennessee Supreme Court reversed his conviction on the narrow ground that only a jury trial could impose a fine exceeding $50, and the law was repealed in 1967.

In 1968, the U.S. Supreme Court overturned an Arkansas state law banning the teaching of evolution. And in 1987, it ruled that states may not require public schools to balance evolution lessons by teaching creationism.

The issue has become a priority for many religious groups, which accuse scientists of stepping outside their field into the realm of theology with some of their pronouncements.

Dover is believed to have been the first school system in the nation to require students to hear about the concept under the policy adopted in October 2004. But the clash over intelligent-design is evident far beyond this rural district of about 3,500 students 20 miles south of Harrisburg.

In August, the Kansas Board of Education gave preliminary approval to science standards that allow intelligent design-style alternatives to be discussed alongside evolution.

President Bush has also weighed in, saying schools should present both concepts.

Richard Thompson, president and chief counsel of the Thomas More Law Center, which is defending the school district, says Dover’s policy takes a modest approach.

It requires teachers to read a statement that says intelligent design differs from Darwin’s view and refers students to an intelligent-design textbook, “Of Pandas and People,” for more information.

“All the Dover school board did was allow students to get a glimpse of a controversy that is really boiling over in the scientific community,” Thompson said.

The Discovery Institute, a Seattle-based think tank that represents scholars who support intelligent design, opposes mandating it in public schools. Nevertheless, it considers the Dover lawsuit an attempt to squelch voluntary debates over evolution.

“It’s Scopes in reverse. They’re going to get a gag order to be placed on teachers across the country,” said institute senior fellow John West.

To build their cases, each side is enlisting a battery of academic experts. Witnesses for the defense include biochemist Michael Behe of Lehigh University, who defended intelligent design in his 1996 book, “Darwin’s Black Box: The Biochemical Challenge to Evolution.”

Eugenie Scott, executive director of the National Center for Science Education, which supports teaching evolution in public schools, said the controversy has little to do with science because mainstream scientists have rejected intelligent-design theory.

Intelligent design supporters “seem to have shifted virtually entirely to political and rhetorical efforts to sway the general public,” Scott said. “The bitter truth is that there is no argument going on in the scientific community about whether evolution took place.”