"We approach it as strictly a scientific topic," he said.

The crux of the ID argument is twofold: that the scientific evidence supporting Darwinian evolution contains flaws and is still open to debate, and that nature is full of evidence showing that there was and is a "designer" at work.

"We don't seek to answer who the designer is," says Crowther. "Just that there is empirical evidence of design in nature."

The designer might be an advanced extraterrestrial civilization, for example, or it could be God, explains Guillermo Gonzalez, an Intelligent Design proponent who is assistant professor of astronomy at Iowa State University. Intelligent Design doesn't start with the assumptions that Creationism does, he says. "But the implications could be religious."

One evidence of a designer, say Intelligent Design scientists such as Lehigh University professor of biological sciences Michael J. Behe, is the concept of "irreducible complexity." Natural selection, he writes, "can only choose among systems that are already working, so the existence in nature of irreducibly complex biological systems poses a powerful challenge to Darwinian theory."

Examples, he says, are the human eye and the flagella of bacteria — both, he says, are systems made up of parts that couldn't exist on their own and therefore did not evolve. Not true, say evolutionary scientists, who argue that the precursor parts of the flagellum and eye could have been favored by natural selection.

"If Behe wishes to suggest that the intricacies of nature, life and the universe reveal a world of meaning and purpose consistent with a divine intelligence," writes Brown University biology professor Kenneth R. Miller in Natural History Magazine, "his point is philosophical, not scientific. It is a philosophical point of view, incidentally, that I share." But the hypothesis of Intelligent Design, he says, "is overwhelmingly contradicted by the scientific evidence."

There is no scientific controversy over evolution, argue these scientists. And to detractors who argue that "evolution is just a theory," they point out that in science "theory" does not mean hunch. "A theory in science," says BYU biology assistant professor Marta Adair, "is not like your theory about why BYU has a lousy basketball team. A theory in science means something nobody has been able to disprove."