A major theme in biological research is the quest for mechanism, embodied in explanatory reductionism: the interpretation of phenomena through links to the entities and laws of more fundamental sciences. For example, the form of Starling's Law of the Heart, relating contractile force to heart volume, follows from the sliding-filament hypothesis of muscle contraction, a molecular concept. Although alternative mechanisms for muscle contraction and cardiac regulation could be deduced from biochemical principles, the formulation provides clear correspondence with the phenomena and (...) a deeper understanding of cardiac function. Moreover, even if the reduction provides no better formulation of the phenomenon, of the macro-regularity, it is still prized as a nearer approach to physical reality, as a step toward realizing fundamental unities and codifying general principles, and as a door to new experimental opportunities. (shrink)