I said in my post about burden of proof (last post, 3 August), that many of the relations among specialties can be seen as a network of settled obligations. At the same, unsettled relations among lines of research can often be seen as disputes about what obligations one specialty has toward the concepts, theories, and methods of another.
Many of the obligations among specialties are quite clear and solid. For example, research in many areas presupposes much of modern physics conceptually, theoretically, and procedurally, via embedding in instruments. It's easy to think up a chain of these dependencies: chemistry is obligated to physics, molecular biology is obligated to chemistry, cell biology is obligated to molecular biology, development is obligated to cell biology, and so on, so that we eventually wind up noticing, e.g., that Da Vinci's Last Supper (1498) is obligated to the physics of sub-atomic particles.