The non-linear nature of this model is best described in terms of the observations of Ilya Prigogine who was awarded the Nobel Prize in 1977 for his work on the thermodynamics of non-equilibrium systems (Prigogine, 1984). Prigogine proposed that all systems contain subsystems, which are continually fluctuating (rising and falling like waves; undulating). He believed that the existing organization of any inanimate open system (i.e., exchanging energy with its environment) could be altered if any given fluctuation or combination of fluctuations became intense enough to introduce a "singular moment" or "bifurcation point." This phenomenon, however, is most likely to occur in systems that are far from thermodynamic equilibrium; that is, they are relatively unstable systems sensitive to small changes. The outcome of an alteration of the pre-existing order of far from equilibrium systems is unpredictable. It could result in either dissolution to a lower energy state (chaos) or establishment of a higher level of organization requiring more energy to sustain than the state it replaced (dissipative structure). The process is non-linear in the sense that the outcome, a dramatic change in energy level, is not proportional to the amount of energy that initiated the change.

This type of reorganization, in which small inputs can initiate profound consequences, is characteristic of the environment in which life exists. Typical examples of the effect on inanimate processes include changes in the weather, earthquakes, or even cosmic events leading to the formation of planets. In these systems, outcome appears to be unpredictable. It has been proposed by Prigogine that the same tendency to re-organize occurs in living systems, as well. The striking difference between inanimate and living systems, however, is that the outcome can be predicted for the latter. In life forms, far from equilibrium systems, such as those regulating temperature in homeotherms, appear to act as subsystems responding dramatically to small changes in order to maintain the overall stability of a higher ordered system. In the case of constant temperature, if the outcome of systems response were unpredictable in life forms as it is with inanimate systems, homeostasis would constantly be threatened. In fact, when system response is compromised in life forms for any variety of reasons, the overall stability of the organism is affected. Inability of the living system to adapt to its constantly changing environment leads to homeostatic disruption that may be severe enough to result in death.

The characteristic predictability of subsystem response to small changes, unique to life, is held by vitalists to be engendered by a "vital force" (innate intelligence, in Chiropractic philosophical terms). It is held that this force imparts a quality to organization, which creates a living system that, as a whole, is more and/or different than the sum of its parts. Many vitalists are also holistic in their perception of life, contending that living organisms react to stimuli in a specific and purposeful manner, often reacting to the same stimulus differently at different times in order to maintain the integrity of the whole (Borregard, 1991).
Humans are in a continuous adaptive flux. It appears that systems critical to life are protected from instability by other systems, which are more sensitive to changes in initial conditions. The living system is thus maintained by numerous subsystems that respond dramatically to environmental (internal and external) challenges. These

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