 In the context of developmental biology, even during the development of a single organism, a structure may be present across time and have a stable developmental-functional role, but its underlying molecular and cellular basis may change (Brigandt 2006, Kirschner 2005). Entities above the molecular level can be more robust so that when some molecular processes change or break down these higher level entities are not modified or removed. Knocking out a gene need not have any impact on ontogeny due to genetic redundancy, while eliminating a particular cell or group of cells may dramatically interfere with normal development (Brigandt 2013a, 2015, Mitchell 2009). A higher level causal connection can be more salient in that the regular operation of the mechanism strongly depends on the presence of this kind of causal relation. Such a higher level causal relation is realized by molecular entities and their interactions (i.e., supervenience obtains), but if relevant higher level processes are less sensitive to disturbance or intervention than certain molecular causes, the more powerful mechanistic explanation can be the one that appeals to more robust, higher level causal connections. This is one reason why some biological sciences preferentially invoke higher level entities and processes in the face of multiple realization, explaining in terms of higher level natural kinds and causes.