But evolution also challenges religious beliefs. The Bible, which teaches that the visible universe was created by God's command over a period of six days, contradicts evolutionary theory. This account, if interpreted literally, makes scientific literacy difficult. Plants, for example, are created before sunlight is created (Genesis 1:11-12; 1:16-18), which means that a literalistic biblical approach to science must challenge the idea of photosynthesis. Stars are created prior to the sun and moon (1:14-15, 1:16-18), which means that a literalistic biblical approach to science must challenge our working cosmological model. And of course if God created all creatures by command (Genesis 1:20-27), land animals before sea animals, then evolution by natural selection and the story it tells becomes a controversial idea.
While many people of faith have been able to reconcile the ideas of literal creation and evolution by natural selection, thinkers on both sides of the debate press the idea that this reconciliation is impossible.
Secular philosopher Daniel Dennett, author of Darwin's Dangerous Idea, has argued that evolution by natural selection renders God superfluous. "The argument for design, I think," he told SPIEGEL in 2005, "has always been the best argument for the existence of God, and when Darwin comes along, he pulls the rug out from under that." Oxford biologist Richard Dawkins, often described (lovingly or derisively) as "the atheist pope" for his objection to religion, once remarked that "around the age of 16, I first understood that Darwinism provides an explanation big enough and elegant enough to replace gods. I have been an atheist ever since." Religious fundamentalists, who also have their objections to metaphorical interpretations of the Book of Genesis, tend to agree that evolutionary theory is a direct threat to the idea of God.
So it's little surprise that controversy has long existed over the teaching of evolution by natural selection in public schools. Fundamentalists initially attempted to ban it, allowing only the biblical account of creation to be taught, but the Scopes "monkey trial" of 1925 made such bans appear ridiculous. Then in Edwards v. Aguillard (1987), the U.S. Supreme Court held that creationism is a religious doctrine and can't be taught in public school biology classes at all. Within two years, supporters of creationism coined the term "intelligent design" as a means of asserting the creationist doctrine outside of the context of religion--asserting that everything was created, but not asserting who it was that did the creating. It could have been God, or it could have been another immensely ancient and powerful creator.
More than twenty years later, we're still more or less there. A smattering of state laws and school board initiatives during the late 1990s and early 2000s attempted to replace the theory of evolution by natural selection with the doctrine of intelligent design in public school biology curricula, or at least to mandate that the two theories be taught side-by-side as equal, but most have lost favor either through public response or local court rulings.
Proponents of intelligent design argue that the theory of evolution by natural selection is itself a religious assertion that denies the doctrine of God as creator. It's hard to say the theory doesn't at least challenge the biblical doctrine of God as creator, in much the same way that astronomical theories of star formation and so forth do, and this does pose a legitimate First Amendment problem: How should public schools teach scientific topics that challenge core religious beliefs? And are they under an obligation to accommodate these beliefs by teaching more religiously inclusive alternative theories?
The answer to this question depends on how you interpret the First Amendment's establishment clause. If you believe that it mandates a "wall of separation between church and state," then the government cannot base its public school biology curriculum on religious considerations. If you believe that it does not, and that some general non-preferential accommodation of religious doctrine is consistent with the establishment clause, then teaching intelligent design as an alternate approach to biology would be legitimate, as long as evolutionary theory is also taught.
My personal belief is that, as a practical consideration, intelligent design should not be taught in public school biology classes. It should, however, be taught in churches. Pastors, particularly youth pastors, have an obligation to become scientifically literate and be prepared, in the words of 1 Peter 3:15, to provide "reason for the hope within." Intelligent design is an evangelism imperative, because a pastor who is not scientifically literate cannot adequately address contemporary challenges to religious faith. That job should not be outsourced to the public school system; as a theological accommodation, intelligent design has no place in a non-sectarian biology curriculum.