 Careful statistical methodology in experiments can answer whether one type of difference maker accounts for more of the variation in the effect variable for a particular population. But a ranking of causal factors with respect to how much of a difference they made is not the same as combining two modes of causation into an integrated account. Another response is to dissolve the integration problem by reducing all of the causal interactions to one of the two distinct modes, thereby achieving a kind of explanatory unity (Rosenberg 2006). However, this approach is eschewed by working biologists who take both genetic and physical modes of causation as significant and not reducible one to the other.