A hierarchical view of natural systems provides an effective framework to describe a given process of interest effectively by focusing a particular hierarchical level. However, this raises a serious problem, how is the focal level restricted or determined by the upper and lower levels? This problem is seen in the theory of natural selection. The theory explains the evolution of a population of biological entities as an automatic consequence of differential heritable fitness among variants, in which the complex biotic/abiotic interactions are put into a black box ("environment"), and the existence of the variants is presupposed; no interactions are explicitly incorporated into this explanation between the focal (population) and the upper/lower levels. In this paper I analyze the inter-level interactions involved in the process of adaptive evolution, and show that it proceeds under upward determination (i.e. generation of novel genetic variants) from the lower level, and under downward one from the upper level such as ecosystem (i.e. supply of new genetic information, creation of selective environments, and dynamic mechanism of replacement).