- Analogies to Natural Systems : The natural system has evolved over many millions of years from a linear (open) system to a cyclical (closed) system in which there is a dynamic equilibrium between organisms, plants, and the various biological, physical, and chemical processes in nature. Virtually nothing leaves the system, because wastes are used as substrates for other organisms.
- Linear (Open) Versus Cyclical (Closed) Loop Systems : The evolution of the industrial system from a linear system, where resources are consumed and damaging wastes are dissipated into the environment, to a more closed system, like that of ecological systems, is a central concept
to industrial ecology