A new challenge to Charles Darwin's theory of evolution is being heard in a federal courtroom in the northeast state of Pennsylvania this week.

At issue is whether an alternative theory to evolution should be taught in the Dover, Pennsylvania school district.

The alternative is known as intelligent design.  Supporters say Darwin's theory of evolution based on natural selection and the survival of the fittest does not fully explain the origin of life.  They argue that the emergence of complex life forms on Earth was the result of an unidentified intelligent force.

Supporters of intelligent design are silent on whether a God-like creator is the instrument for creation.

But supporters of Darwin's theory of evolution contend that intelligent design is nothing more than a new twist on creationism, the belief that God created the world as told in Genesis in the Christian Bible.

Barrie Callahan is one of 11 parents who are trying to prevent the Dover school board from including the theory of intelligent design in high school classes on biology.

"Religion cannot be in science class.  Science is not about who.  Science is about what," said Mr. Callahan.

Experts who support Darwin's view of evolution have testified at the trial that virtually every prominent scientific organization in the United States supports evolution by natural selection as an unshakeable pillar of modern science.

Nick Matzke is with a group called the National Center for Science Education.

He says supporters of intelligent design want to mix religion and science.

"Intelligent design is just a new label for creationism," Mr. Matzke noted.  "It is just the latest legal strategy for creationism.  It evolved in 1987 right after the Supreme Court ruled against creationism and said that that was unconstitutional."

Supporters of intelligent design contend the issue is not about God but about the right to present an alternative view of evolution to students.

Richard Thompson is a lawyer defending the right of the Dover school board to include references to intelligent design in the school system's science classes.

"What the theory of intelligent design says is, looking at the complex nature, it could not have happened by random chance," said Mr. Thompson.  "It could not have happened by Darwin's theory of natural selection."

The Supreme Court banned the teaching of the religious based theory of creationism in public schools in 1987, ruling that it violated the constitutional mandate of keeping church and state separate.

Lawyer Richard Thompson says that students should know there is a debate about the origins of life and that they should be exposed to the theory of intelligent design.

"It is good education to allow students to know that there is a controversy surrounding biological evolution," added Mr. Thompson.

Advocates on both side of the case believe it is likely that the issue will one day wind up being argued before the Supreme Court.