This article exposes surprisingly close historical parallels in the development of Intelligent Tutoring Systems (ITS) based on biologically inspired ACT-R theories and dynamically adaptive tutoring systems based on operationally defined cognitive constructs that serve as a foundation for the Structural Leaning theory (SLT). The article begins with a comparison of geocentric Ptolemaic and heliocentric Copernican theories of the solar system. The article then traces surprisingly close parallels over the past half century in the development of ACT-R and SLT and the dynamically adaptive tutoring systems spawned by each. The former work from the bottom-up; the latter work from the top-down. Retracing history shows that the former, ACT-R theories and ITS systems based thereon, result in precise albeit complex accounts of observable behavior and ITS systems based thereon. The latter, SLT and the AuthorIT authoring and TutorIT delivery systems based thereon, result in equally precise but more cohesive and more easily constructed dynamically adaptive tutoring systems.