Hierarchical organization is an essential characteristic of living things. Although most biologists affirm the concept of living things as hierarchically organized structures, there are widespread differences of interpretation in the meaning of hierarchy and of how the concept of hierarchy applies to living things. One such basic difference involves the distinction between the concept of control hierarchy and classification hierarchy. It is suggested that control hierarchies are distinguished from classification hierarchies in that while the former involve authority relationships between levels, (...) the latter do not. This is illustrated in an analysis of proposed hierarchies of replicators and interactors.The analysis of levels of hierarchies and their relationships also brings up the part-whole problem. An authority relationship between levels implies that the whole has a determining influence on the parts that make up the whole, and that parts have no independent, meaningful existence apart from the whole. The concept of an authority relationship in a part-whole relationship introduces the question of the independence or sovereignty of the components of the subordinate levels in a hierarchically organized living thing. This problem is discussed along with an analysis of the rather novel theory of enkapsis proposed by H. Dooyeweerd, in which he distinguishes part-whole relationships from enkaptic relationships. (shrink)