Philosophical naturalism is not merely a gratuitous conclusion that neo-Darwinists draw from their scientific theory; rather, it is the powerful metaphysical basis of the theory itself. How do Darwinists know that natural selection, in combination with random mutations, can produce such apparent wonders of design as the wing, the eye, and the brain? How do they know that preexisting intelligence was not required to produce life in the first place, to guide unicellular life in its progress to more complex forms, and to develop eventually the human mind? In fact Darwinists do not know these things by experiment, or by any other form of scientific investigation. They know them by philosophical presupposition, because their naturalism tells them that nature cannot be affected by anything outside nature. Darwinism is not merely a support for naturalistic philosophy: it is a product of naturalistic philosophy.