 This anatomy of problems, with explicit epistemological structure derived from different values for these variables, operates to organize the science of development. Investigators from different disciplines can be working on the same problem but asking different questions that require distinct but complementary methodological resources. Knowledge and inquiry in developmental biology are intricately organized, just not by a central theory or group of models, and this erotetic organization is epistemologically accessible to the participating scientists. While theoretical knowledge, especially that drawn from molecular biological mechanisms (see the entry on  molecular biology)  and mathematical models (e.g., reaction–diffusion models) is ubiquitous (theory-informed), the clusters of problems that reappear across the textbooks and correspond to different types of processes provide the governing architecture (not theory-directed), which can be characterized explicitly according to the variables described. Further analysis of this problem anatomy is possible, including how it is displayed in regular research articles and not just textbooks, as well as other areas of biology (see, e.g., Brigandt and Love 2012).