 Lindley Darden and Nancy Maull were at the forefront of this discussion with the concept of an  inter-field theory  (Darden and Maull 1977, Maull 1977). For example, the advent of the chromosome theory of inheritance in the 1910s bridged the previously unrelated fields of Mendelian genetics (which studied phenotypic patterns of inheritance across generations) and cytology (which dealt with the material contents of cells). This interfield theory effected a kind of unification, but Mendelian genetics and cytology were not reduced to each other, nor did the interfield theory reduce both fields. More recent work has articulated interfield relations without relying on the notion of a theory (Bechtel 1986, Burian 1993, Grantham 2004a, 2004b, Mitchell 2002). This parallels the trend in models of explanatory reduction of moving away from theories as the only epistemic units of interest  (Section 3.2),  but the emphasis is on relata such as coordination, integration, synthesis, or reciprocal interaction (Bechtel 2013, Love and Lugar 2013, Plutynski 2013). A rationale for these relata emerges from the demand for multidisciplinary research; the explanatory task involves coordinating diverse epistemic resources, which amounts to an implicit rejection of the “fundamentality” of one particular discipline producing the most empirically adequate explanations.