Darwin's Origin

paley William Paley, who lived from 1743 to 1805, was one of the most influential English authors of his time. He argued forcefully in his Natural Theology (1802) that the complex and precise design of organisms and their parts could be accounted for only as the deed of an Intelligent and Omnipotent “Designer.” The design of organisms, he argued, was incontrovertible evidence of the existence of the Creator. Paley was an English clergyman intensely committed to the abolition of the slave trade and, by the 1780s, had become a much soughtafter public speaker against slavery. He was also an influential writer of works on Christian philosophy, ethics, and theology. The Principles of Moral and Political Philosophy (1785) and A View of the Evidences of Christianity (1794) earned him prestige and the kind of ecclesiastical benefices that allowed him a comfortable life. In 1800, Paley gave up his public speaking career for health reasons, providing him ample time to study science, particularly biology , and to write Natural Theology; or, Evidences 371 Francisco J. Ayala NONFICTION Darwin’s rigin O 372 Ecotone: reimagining place of the Existence and Attributes of the Deity, Collected from the Appearances of Nature, the book by which he has become best known to posterity and which would greatly influence Darwin. With Natural Theology, Paley sought to update the work of another English clergyman, John Ray, author of Wisdom of God Manifested in the Works of the Creation (1691). But Paley could now progress beyond Ray by taking advantage of a century of additional biological knowledge. Natural Theology is a sustained argument for the existence of God based on the obvious design of humans and their organs, as well as the design of all sorts of other organisms, considered by themselves and in their relations both to one another and to their environments. The argument is twofold: First, organisms give evidence of having been designed; second, only an omnipotent God could account for the perfection, multitude, and diversity of the designs. There are chapters dedicated to the complex design of the human eye; to the human frame, which displays a precise mechanical arrangement of bones, cartilage, and joints; to the circulation of the blood and the disposition of blood vessels; to the comparative anatomy of humans and animals; to the digestive tract, kidneys, urethras, and bladder; to the wings of birds and the fins of fish; and much more. For 352 pages, Natural Theology conveys Paley’s extensive and accurate biological knowledge, as expertly as was possible in 1802. After detailing the precise organization and exquisite functionality of each biological entity, relationship, or process, Paley draws again and again the same conclusion , that only an omniscient and omnipotent Deity could account for these marvels of mechanical perfection, purpose, and functionality, and for the enormous diversity of inventions that they entail. Paley’s first model example is the human eye. Paley points out that the eye and the telescope “are made upon the same principles; both being adjusted to the laws by which the transmission and refraction of rays of light are regulated.” Specifically, there is a precise resemblance between the lenses of a telescope and “the humors of the eye” in their figure, their position, and their ability to converge the rays of light at a precise distance from the lens—on the retina in the case of the eye. The eye consists “first, of a series of transparent lenses—very different, by the by, even in their substance, from the opaque materials of which the rest of the body is, in general at least, composed.” Second, the eye has the retina, which as Paley points out is the only membrane in the body 373 francisco j. ayala that is black, spread out behind the lenses, so as to receive the image formed by pencils of light transmitted through them, and “placed at the precise geometrical distance at which, and at which alone, a distinct image could be formed, namely, at the concourse of the refracted rays.” Third, he writes, the eye possesses “a large nerve communicating between this membrane [the retina] and the brain; without which, the action of light upon the membrane, however modified by the...