The Galápagos tortoise helped Charles Darwin formulate his theory of evolution. So did the work of theologian William Paley. (Reuters)

Earlier this week, young-earth creationist Ken Ham and “Science Guy” Bill Nye engaged in a well-publicized debate at the Creation Museum in Kentucky. It was generally been framed as a contest between science and religion — or, as Mark Joseph Stern suggested at Slate, “Science vs. Fiction.” Even televangelist Pat Robertson weighed in to tell Ham that his young-earth creationism was not just false, but humiliatingly stupid. "To say that it all came about in 6000 years is just nonsense," Robertson said on his show, The 700 Club. " Let’s be real, let’s not make a joke of ourselves."

Creationism continues to have currency among a significant proportion of the American public, even though it has never had any scientific basis. The ferocity of the debate makes it difficult to remember that, at one point not so long ago in geological time, religion and science weren't all that distinct. In the late 1600s and early 1700s, intelligent design — the belief that you could find God's hand by examining creation — was seen as a way to glorify both God and the ordered laws of physics revealed by Newton.

The most sophisticated form of the intelligent design argument, however, wasn't based on Newtonian physics. It was based in biology. In 1802, a theologian named William Paley published his tome Natural Theology. Hume had shot largish holes in the Newtonian design argument, and Paley as a consequence granted that astronomy was "not the best medium through which to prove the agency of an intelligent Creator." But, he argued, it was still possible to see purpose in the universe by looking to animal and human life.

Each creature, Paley argued, was uniquely shaped to its environment in a way that showed a kind of intimate care. Moles have feet that function as "so many shovels," to allow them to dig through the earth. "Maggots" are perfectly equipped to "revel in putrefaction." The human "gall-duct into the duodenum" is structured to have "a necessary mechanical tendency to resist regurgitation." Animals are adapted so that their sleep cycles fit into the movement of day and night, a fact which for Paley "connects the meanest individual with the universe itself: a chicken roosting upon its perch, with the spheres revolving in the firmament."

It's easy to laugh at Paley's enthusiasms; he was probably laughing at them himself to some extent. (I have to believe he chuckled a little at that bit about maggots reveling in putrefaction.) But while his reasoning can appear amusing in retrospect, Natural Theology was a hugely important work, not only for its own day, but for ours. The way Paley formulated the design argument essentially split God in two: there was a lawgiver, who set in place the physical universe and the motion of the spheres, and there was a creator, who shaped individual creatures, whether humans or chickens roosting on their perches, to fit those laws. As John Durant wrote in Darwinism and Divinity: Essays on Evolution and Religious Belief, "by pushing God Himself into the background, and entrusting the enforcement of the 'rules of creation' to an intelligent subordinate ... Paley unwittingly transformed his defence of theism into a model of naturalistic explanation."

That "naturalistic explanation" is only a step away from Darwin's natural selection. And, in fact, it probably is a version of natural selection, in that there's every reason to believe that Darwin was informed by Paley's work. Paley's books were used extensively in the undergraduate curriculum at Christ's College (Paley's college as well as Darwin's), and Darwin remembered them fondly in his autobiography. It shouldn't be surprising, then, that the questions Darwin was answering were ones that Paley had posed, and the observations he was making were ones that Paley had developed. Intelligent design wasn't something invented after Darwin to oppose him; rather, it was the context for, and a building block of, his work.

Intelligent design, then, is not some sort of anti-science, know-nothing idiocy. It's an important part of the history of science, and a necessary link in the development of Darwin's elegant theory of evolution. If birds are dinosaurs, Bill Nye is an intelligent design theologian.

That may be a bitter truth to swallow for some anti-Creationists. But the history of intelligent design raises even more uncomfortable questions for Biblical literalists like Ken Ham. Paley and his intelligent design predecessors were not, in any sense of the term, evangelical enthusiasts. On the contrary, the history of intelligent design, from Clarke through Darwin, is a history of creeping atheism. The early post-Newton forms of the argument were often associated with deism. Samuel Clarke was publicly censured for un-trinitarian opinions — he didn't believe in the divinity of Christ. Paley was cagey about his own theological commitments, but there's good reason to think they weren't far out of line with Clarke's— he caused a stir at Christ's College as a student when he proposed in a 1762 public debate to argue against the eternity of Hell's torments.

And then there's this passage from Paley's The Natural Theology:

It is a happy world after all. The air, the earth, the water, teem with delighted existence. In a spring noon, or a summer evening, on whichever side I turn my eyes, myriads of happy beings crowd upon my view. ‘The insect youth are on the wing.’ Swarms of new-born flies are trying their pinions in the air. Their sportive motions, their wanton mazes, their gratuitous activity, their continual change of place without use or purpose, testify their joy, and the exultation which they feel in their lately discovered faculties ... Other species are running about, with an alacrity in their motions, which carries with it every mark of pleasure ... If we look to what the waters produce, shoals of the fry of fish frequent the margins of rivers, of lakes, and of the sea itself. These are so happy, that they know not what to do with themselves. Their attitudes, their vivacity, their leaps out of the water, their frolics in it (which I have noticed a thousand times with equal attention and amusement), all conduce to show their excess of spirits, and are simply the effects of that excess.

Paley's biographer, D.L. LeMahieu pointed out that this reads like Wordsworthian pantheism. It's a vision of romantic, organic spirituality, largely independent of a specifically Christian God.

Ham's aware of some of these tensions, and has written dourly that intelligent design "is not a Christian movement." But distance himself as he will, Ham's project continues, as creationist G. Shane Morris says, to use nature as "a kind of baptized laboratory where the goal is to compel the evidence of the natural world to support a certain Scriptural hermeneutic." That was broadly Paley's goal as well. Ham, almost despite himself, is working in a tradition of intelligent design that has as much to do with deistic spiritualism as with the Bible. To the discomfort of both, the scientist and the Christian apologist are both Paley's children.