As "the last of the natural theologians," argues David Kohn (1989, 238), Charles Darwin was "the man who turned out the lights." In one sense this claim is accurate: classical natural theology in England, as typified by the Bridgewater Treatises, largely disappeared after 1859. In another sense, however, the claim is false, and lights have been burning all the while. Theological assumptions have deeply informed evolutionary reasoning from the Darwinian Revolution to the present day, and their persistence challenges methodological naturalism both as a descriptive thesis and as a normative epistemological ideal.
Theological puzzles were a key aspect of Darwin's argument for a fully naturalistic process of descent with modification (Gillespie 1979, Kitcher 1985). Indeed, not only the Origin of Species, but large portions of the rest of Darwin's published and unpublished corpus are inexplicable unless seen against the theological background which provides certain of his arguments and speculations with their premises. A wise and benevolent Creator would have brought into being a world with particular qualities; we do not observe such a world; therefore either the world was not created, or the Creator acted in indirect modes via natural laws and secondary causes. This reasoning fills Darwin's writings.
Yet, as Hull (1983, 65) points out, the Darwinian Revolution was "as much concerned with the promotion of a particular view of science as it was with the introduction of a theory of the transmutation of species." That view of science was methodological naturalism: in scientific explanation and theory justification, one can appeal only to natural causes or chance. Plainly, methodological naturalism sits uncomfortably with the theological content of Darwin's reasoning. Nevertheless, in practice, evolutionary biologists have ignored the rule of naturalism and have followed Darwin's lead. Biology textbooks and the professional literature today continue to justify evolution by referring to the world expected of a benevolent Creator, which, it is contended, we do not observe (Gould 1980; Jacob 1982; Burian 1986).
I suggest that in evolutionary biology, methodological naturalism as a rule of reasoning has been held opportunistically at best. Darwin's philosophical revolution was, and is, incomplete because the revolution has been taking supplies from the storehouse of the theological ancien regime all along. Now one might argue that Darwinian theological arguments should be expelled at last from evolutionary reasoning. I argue, on the other hand, that the rule of methodological naturalism is unsound on its face, and that scientific inquiry will continue happily, if not without its usual difficulties, if the rule is ignored.
Copyright © Paul A. Nelson