The most important concept within ecology is the ecosystem. This concept has changed over time, but the currently accepted definition is that the ecosystem is a physically locatable and quantifiable community formed by a system of energy exchange between the living, the dead, and the never-living where, when energy animates the system, there is an exchange of energy and material between the living and the dead.¹ It is not often understood that this concept, the most important and foundational within ecology, was created in response to the overdetermination of ecology by two schools of thought: organicism and mechanism. These schools of thought are philosophical and theological in their make-up and concern the reality of nature as such. The ecosystem concept is first articulated in 1935 by A. G. Tansley in his unification of these two rival schools of thought as they were understood and shaped by the material and stance of ecology. The organicists, primarily developed in and from the work of F. E. Clements, were opposed by the individualist reaction against organicism of Henry Gleason and his followers. In Clements's view the ecosystem, which he named "biome," was like a single organism where all the parts worked toward the health of the whole. Whereas Gleason rejected this organic view of nature and instead proposed that natural communities of plants are simply a random grouping of individual species that existed in that place because of the possibility of satisfying their needs, Tansley rejected the organicism of Clements, but could not follow the coincidentalism of Gleason, which constituted a decisive critique of Clements's views but did not provide any satisfactory understanding of the relation between plant communities.