HARRISBURG, Pa. -- A Lehigh University biochemistry professor and leading advocate of intelligent design testified Monday that evolutionary theory should be taught to science students.

But, he said it alone cannot explain complex biological phenomena.

Professor Michael Behe was the first witness called by the Dover Area school board Monday in a landmark federal trial over whether intelligent design can be mentioned in public school science classes as an alternative to the theory of evolution.

The Dover school board requires students to hear a statement about the intelligent design concept in biology class.

Eight families are suing to overturn the requirement.

The trial began Sept. 26 and is expected to last up to five weeks.

Behe said students should be taught evolution because it's widely used in science and that, "any well-educated student should understand it."

But Behe also argued that evolution cannot fully explain the biological complexities of life, thus suggesting the work of an intelligent force.

The intelligent design theory does not name the designer, although Behe, a Roman Catholic, testified he personally believes it to be God.

Behe's work includes a 1996 best-seller called "Darwin's Black Box."