 Finding philosophical models for the explanatory integration of genetics and physics remains an open question (Love 2017b). Apportioning causal responsibility in the sense of determining relative contributions (e.g., the composition of causal magnitudes among different physical forces in Newtonian mechanics) is problematic because this requires commensurability with respect to how causes produce their effects (Sober 1988). In the context of causation understood in terms of difference makers, the difficulty of integration is a variation on a problem in causal reasoning identified by John Stuart Mill and labeled the “intermixture of effects,” which involves multiple causes contributing in a blended fashion to yield an outcome.