Naturalism, the idea that reality is formed solely by natural processes, consists solely of natural beings and objects, and governed solely by natural laws, is a philosophy that developed as science developed. Modern science did not, at first, rely upon naturalism. Galileo fully believed that the physical laws he discovered were created by God as part of the universe, and Isaac Newton could ascribe physical phenomena to supernatural control if a natural explanation was not known and could not be conceived. The origin and functioning of the universe, solar system, Earth, plant and animal species, and humans were routinely ascribed to supernatural processes by legitimate scientists well into the nineteenth century, as the histories of catastrophism and creationism clearly reveal. Following the examples of Galileo and Newton... scientists such as Laplace, Hutton, Lyell, Darwin, and Huxley slowly and sequentially attempted to explain the origin and functioning of these real objects and beings solely by natural explanations. Naturalism as a necessary part of science thus developed gradually as science developed gradually with the practice and understanding of scientists; appreciation of the hypothetico-deductive method and empirical testing of hypotheses requires naturalism, since supernatural claims cannot be tested.