Ontogeny and Phylogeny is Stephen Jay Gould's first technical book, published in 1977 by Belknap, a division of Harvard University Press. Gould wrote that Ernst Mayr suggested in passing that he write the book, but that Gould "only began it as a practice run to learn the style of lengthy exposition before embarking on my magnum opus about macroevolution." This became The Structure of Evolutionary Theory, published in 2002.