In The Variation of Animals and Plants under Domestication, published in 1868, Darwin used the metaphor of the architect to argue in favor of natural autonomy and to clarify the role of chance in his theory of adaptive change by variation and natural selection. In this article, I trace the history of this important heuristic instrument in Darwin's writings and letters and suggest that this metaphor was important to Darwin because it helps him to explain the role of chance, and (...) gives an argument in favor of the free will. (shrink)