Under the terms of the will of the Oxford scholar Francis Henry, Earl of Bridgewater (1756-1829), Fellow of the Royal Society, absentee rector and keen manuscript-collector, a series of books was commissioned, designed to contribute to an understanding of the world as created by God. In 1834 Peter Roget, who was at the time compiling his celebrated Thesaurus, contributed a two-volume treatise to that controversial series, which formed part of the complex intellectual background to Darwin's work on evolution. Roget described, in a manner designed to appeal to a wide audience, the variety and complexity of the plant and animal kingdoms, focussing on mechanics in the first volume and physiology in the second. The interconnected functions of individual plants and animals are seen as proving God's design. The arguments found here resonate with debates that continue today, as well as providing source material for historians of science.