 The ZFEL also raises some fundamental philosophical questions about the structure of evolutionary theory. How, for example, should we determine what counts as the default expectation, or zero-force condition, for an evolutionary system (Gouvêa 2015)? Is there any way to distinguish empirically between theories that disagree about the default expectation? Is there even a fact of the matter about what the default expectation should be? These questions about default expectations for evolutionary systems may link up with larger questions about the function of null hypotheses in scientific reasoning. These questions about default assumptions in macroevolutionary theory also prompt comparison with questions about, for instance, neutral theory in molecular evolution (Kimura 1983) and in community ecology (Hubbell 2006). For relevant philosophical discussion, see e.g., Dietrich (1994); Bausman and Halina (2018).