This paper is concerned with the uses of history in science. It focuses in particular on Anglo-American genetics and on university textbooks—where the canon of a science is consolidated, as the heterogeneous approaches and controversies of its practice are rendered unified for its reproduction. Tracing the emergence and eventual standardization of geneticists’ use of a case-based method of teaching in the 1920s–1950s, this paper argues that geneticists created historical environments in their textbooks—spaces in which students developed an understanding of the (...) laws of genetics through simulations of their discovery and use. Witnessing the unfolding of Mendel’s and Morgan’s experiments and performing genetic crosses on paper, students learned not only the rules that were explicitly taught as such, but also the experientially-based, tacit skills needed to find and follow these rules. This didactic system taught them how to go on when confronting new situations, and in doing so, provided geneticists with an important disciplinary tool, freeing the first steps of their student’s enculturation from the physical infrastructure of the laboratory. (shrink)