Thoughts in a Haystack

The strength of the argument against chance derives, [William] Paley tells us, from what he names "relation," a notion akin to what some contemporary authors have named "irreducible complexity." This is how Paley formulates the argument for irreducible complexity: "When several different parts contribute to one effect, or, which is the same thing, when an effect is produced by the joint action of different instruments, the fitness of such parts or instruments to one another for the purpose of producing, by their united action, the effect, is what I call relation; and wherever this is observed in the works of nature or of man, it appears to me to carry along with it decisive evidence of understanding, intention, art" (Natural Theology, p. 175–176). The outcomes of chance do not exhibit relation among the parts or, as we might say, they do not display organized complexity. He writes that "a wen, a wart, a mole, a pimple" could come about by chance, but never an eye; "a clod, a pebble, a liquid drop might be," but never a watch or a telescope.

Paley notices the "relation" not only among the component parts of an organ, such as the eye, the kidney, or the bladder, but also among the different parts, limbs, and organs that collectively make up an animal and adapt it to its distinctive way of life: "In the swan, the web-foot, the spoon bill, the long neck, the thick down, the graminivorous stomach, bear all a relation to one another. ... The feet of the mole are made for digging; the neck, nose, eyes, ears, and skin, are peculiarly adapted to an under-ground life. [In a word,] this is what I call relation."

- Francisco J. Ayala, "Darwin's greatest discovery: Design without designer," PNAS, May 9, 2007