"The living systems are a special subset of the set of all possible concrete systems. They are composed of the monerans, protistans, fungi, plants, animals, groups, organizations, societies, and supranational systems. They all have the following characteristics:

(a) They are open systems, with significant inputs, throughputs, and outputs of various sorts of matter-energy and information.

(b) They maintain a steady state of negentropy even though entropic changes occur in them as they do everywhere else. This they do by taking in inputs of foods or fuels, matter-energy higher in complexity or organization or negentropy, i.e., lower in entropy, than their outputs. The difference permits them to restore their own energy and repair breakdowns in their own organized structure. Schrodinger said that "What an organism feeds upon is negative entropy. " [What Is Life?] ...

(c) They have more than a certain minimum degree of complexity.

(d) They either contain genetic material composed of deoxyribonucleic acid (DNA), presumably descended from some primordial DNA common to all life, or have a charter. One of these is the template - the original "blueprint" or "program" - of their structure and process from the moment of their origin.

(e) They are largely composed of an aqueous suspension of macromolecules, proteins constructed from about 20 amino acids and other characteristic organic compounds, and may also include nonliving components.

(f) They have a decider, the essential critical sub-system which controls the entire system, causing its subsystems and components to interact. Without such interaction under decider control there is no system.

(g) They also have certain other specific critical sub-systems or they have symbiotic or parasitic relationships with other living or nonliving systems which carry out the processes of any such subsystem they lack.

(h) Their subsystems are integrated together to form actively self-regulating, developing, unitary systems with purposes and goals.

(i) They can exist only in a certain environment. Any change in their environment of such variables as temperature, air pressure, hydration, oxygen content of the atmosphere, or intensity of radiation, outside a relatively narrow range which occurs on the surface of the earth, produces stresses to which they cannot adjust. Under such stresses they cannot survive."

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