© 2004 Robert A. Freitas Jr. and Ralph C. Merkle. All Rights Reserved.

Robert A. Freitas Jr., Ralph C. Merkle, Kinematic Self-Replicating Machines, Landes Bioscience, Georgetown, TX, 2004.

5.1.2 Miller Critical Subsystems of Living Systems (1978)

Seeking to devise a “general theory of living systems,” in 1978 the late James Grier Miller [2393, 2394] set forth a conceptual framework in which living systems at all size scales are defined as “open systems composed of subsystems which process inputs, throughputs, and outputs of various forms of matter, energy, and information.“ Miller identified 19 critical subsystems whose processes are deemed essential for life and which together comprise a living system. Most of the 19 subsystems are found at all hierarchical levels of living systems, running through cells, organs, organisms, groups, organizations, societies, and even supranational systems. However, not all of these subsystems are strictly essential for self-replication, so disabling or removing some of them results in a system capable of replication only in limited circumstances, which is more desirable from a commercial or public safety viewpoint [271]. (For example, an externally-controlled replicator would not need an onboard Decider subsystem.) Space does not permit more than a listing and brief description of each of the 19 critical subsystems, taken verbatim from Miller’s discussion [2393]:

Subsystems which process both matter-energy and information

(1) Reproducer – the subsystem which is capable of giving rise to other systems similar to the one it is in. This process fundamentally involves transmission of information, the template of the new system. The matter-energy which is organized to compose the new system, however, must also be processed. The care of the next generation of systems until they become independent and self-supporting is also a function of this subsystem. In all systems the reproducer operates by many complex, reversible functions, but the ultimate effect is to bring about an irreversible, historical change, the creation of the new systems of a new generation.

(2) Boundary – the subsystem at the perimeter of a system that holds together the components which make up the system, protects them from environmental stresses, and excludes or permits entry to various sorts of matter-energy and information.

Subsystems which process primarily matter-energy

(3) Ingestor – the subsystem which brings matter-energy across the system boundary from the environment.

(4) Distributor – the subsystem which carries inputs from outside the system or outputs from its subsystems around the system to each component.

(5) Converter – the subsystem which changes certain inputs to the system into forms more useful for the special processes of that particular system.

(6) Producer – the subsystem which forms stable associations that endure for significant periods among matter-energy inputs to the system or outputs from its converter, the materials synthesized being for growth, damage repair, or replacement of components of the system, or for providing energy for moving or constituting the system’s outputs of products or information markers to its suprasystem.

(7) Matter-Energy Storage – the subsystem which retains in the system, for different periods of time, deposits of various sorts of matter-energy.

(8) Extruder – the subsystem which transmits matter-energy out of the system in the forms of products or wastes.

(9) Motor – the subsystem which moves the system or parts of it in relation to part or all of its environment, or moves components of its environment in relation to each other.

(10) Supporter – the subsystem which maintains the proper spatial relationships among components of the system, so that they can interact without weighting each other down or crowding each other.

Subsystems which process primarily information

(11) Input Transducer – the sensory subsystem which brings markers bearing information into the system, changing them to other matter-energy forms suitable for transmission within it.

(12) Internal Transducer – the sensory subsystem which receives, from subsystems or components within the system, markers bearing information about significant alterations in those subsystems or components, changing them to other matter-energy forms of a sort which can be transmitted within it.

(13) Channel and Net – the subsystem composed of a single route in physical space, or multiple interconnected routes, by which markers bearing information are transmitted to all parts of the system.

(14) Decoder – the subsystem which alters the code of information input to it through the input transducer or internal transducer into a “private“ code that can be used internally by the system.

(15) Associator – the subsystem which carries out the first stage of the learning process, forming enduring associations among items of information in the system.

(16) Memory – the subsystem which carries out the second stage of the learning process, storing various sorts of information in the system for different periods of time.

(17) Decider – the executive subsystem which receives information inputs from all other subsystems and transmits to them information outputs that control the entire system.

(18) Encoder – the subsystem which alters the code of information input to it from other information processing subsystems, from a “private“ code used internally by the system into a “public“ code which can be interpreted by other systems in its environment.

(19) Output Transducer – the subsystem which puts out markers bearing information from the system, changing markers within the system into other matter-energy forms which can be transmitted over channels in the system’s environment.

Last updated on 1 August 2005