 Waters (1990) challenges the commitment to unification that implies there is explanatory loss in appealing to the multiply realized “gory details” of molecular biology. In some cases, disjunctive explanations at a lower level seem to explain better than unified explanations at higher levels. Elliott Sober (1999) extends this line of argument: an explanation in terms of higher level kinds can be more unified or general by encompassing heterogeneous lower level kinds, but this same heterogeneity exhibits important differences in scientifically interesting properties. Only the lower level science can account for such differences and therefore, in this sense, offers a deeper explanation than the higher level science. Explanations are not better or worse along a one-dimensional scale. There are several epistemic virtues an explanation can possess, such as generality, depth, or specificity. Sometimes a lower level explanation is better relative to one epistemic virtue, while a higher level explanation is preferable relative to another, such as unification. And unification itself can be explicated differently in terms of functional or structural features of biological systems (see, e.g., Weiskopf  2011).[12] 