On this date, William Paley was ordained as an Anglican priest. He was a prolific author, but his most influential contribution to biological thought was his book Natural Theology: or, Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature, first published in 1802. He introduced one of the most famous metaphors in the philosophy of science, the image of the watchmaker:
. . . when we come to inspect the watch, we perceive. . . that its several parts are framed and put together for a purpose, e.g. that they are so formed and adjusted as to produce motion, and that motion so regulated as to point out the hour of the day; that if the different parts had been differently shaped from what they are, or placed after any other manner or in any other order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it. . . . the inference we think is inevitable, that the watch must have had a maker – that there must have existed, at some time and at some place or other, an artificer or artificers who formed it for the purpose which we find it actually to answer, who comprehended its construction and designed its use.
Even Charles Darwin commented on Paley in his Autobiography:
In order to pass the B.A. examination, it was, also, necessary to get up Paley’s Evidences of Christianity, and his Moral Philosophy… The logic of this book and as I may add of his Natural Theology gave me as much delight as did Euclid. The careful study of these works, without attempting to learn any part by rote, was the only part of the Academical Course which, as I then felt and as I still believe, was of the least use to me in the education of my mind. I did not at that time trouble myself about Paley’s premises; and taking these on trust I was charmed and convinced of the long line of argumentation.
Natural theology had dominated English thinking for nearly two centuries, Paley’s arguments going back to authors such as John Ray, and have had a long intellectual history, surviving to the present day in many a piece of creationist rhetoric. Although totally discredited in modern science, natural theology was important scientifically because it guided researchers to the fundamental question of how life works. Even today, when scientists discover a new kind of organ or protein, they try to figure out its function.