Underlying the ecologic hierarchy is a genetic hierarchy that is ultimately based on nucleotides which are organized into units of heredity. From these units the ecological hierarchy proceeds to levels that include the individual organism, the niche, the ecosystem, the 'biome', and the biosphere. Each level can be considered as a system of which the units of the preceding level form parts. Such systems can be described nearly independently. Each of these systems may evolve by means of changes in the relations among its largest subsystems. Evolution of the more inclusive levels includes changes in the relationships among the subsystems of all the lower levels as well. Thus, some information about the most inclusive level may be gained from studying the least inclusive. The entire hierarchy, however, evolves in concert, and study of the more inclusive systems may shed light upon pathways of evolution of the less inclusive.

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