F. Capra
The Web of Life

A New Synthesis of Mind and Matter

Structural Coupling 

Wherever we see life, from bacteria to large-scale ecosystems, we observe networks with components that interact with one another in such a way that the entire network regulates and organises itself.  Since these components, except for those in cellular networks, are themselves living systems, a realistic picture of autopoietic networks must include a description of how living systems interact with one another and, more generally, with their environment.

Structural Changes

The central characteristic of autopoietic system is that it undergoes continual structural changes while preserving its weblike pattern of organisation.  The components of the network continually produce and transform one another, and they do so in two distinct ways.

1 One type of structural changes are changes of self-renewal.  Every living organism continually renews itself, cells breaking down and building up structures, tissues and organs replacing their cells in continual cycles.  In spite of this ongoing change, the organism maintains its overall identity, or pattern of organisation.

Many of these cyclical changes occur much faster than one would imagine.  For example, our pancreas replaces most of its cells every 24 hours, our stomach lining every three days, are white blood cells are renewed in 10 days and 98 percent of the protein in our brain is turned over in less than one month.

2 The second type of structural changes in the living system are changes in which new structures are created - new connections in the autopoietic network.  These changes of the second type - developmental rather than cyclical - also take place continually, either as a consequence of environmental influences or as a result of the systems internal dynamics.  According to the theory of autopoiesis, the living system interact with its environment through "structural coupling", i.e. through recurrent interactions, each of which triggers structural changes in the system.

For example, a cell membrane continually incorporates substances from the environment into the cells metabolic processes.  The organism's nervous system changes its conductivity with every sense perception.  These living systems are autonomous, however.  The environment only triggers the structural changes, it does not specify or direct them.

Structural coupling establishes a clear difference between the ways living and nonliving systems interact with their environments.  Kicking a stone and and kicking a dog are two very different stories, as Gregory Bateson was fond of pointing out. The stone will react to the kick according to a linear chain of cause and effect.  It's behaviour can be calculated by applying the basic laws of Newtonian mechanics.  The dog will respond with structural changes according to its own nature and (non-linear) pattern of organisation.  The resulting behaviour is generally unpredictable.

As a living organism responds to the environmental influences with structural changes, these changes will in turn alter its future behaviour.  In other words, is structurally coupled system is a learning system.

As long as it remains alive, the living organism will couple structurally to its environment.  Its continual structural changes in response to the environment - and consequently its continuing adaption, learning and development - are key characteristics of the behaviour of living beings.  Because of its structural coupling, we call the behaviour of an animal intelligent but would not apply that termed to the behaviour of a rock.

As it keeps interacting with its environment, a living organism will undergo a sequence of structural changes, and over time it will form its own, individual pathway of structural coupling. 
At any point on this pathway, the structure of the organism is a record of previous structural changes and thus of previous interactions.  Living structure is always a record of previous development, and ontogeny - the course of development of an individual organism - is the organism is history of structural changes.

Since the organism structure at any point in its development is a record of its previous structural changes, and since each structural change influences the organismís future behaviour, this implies that the behaviour of the living organism is determined by its structure. 

Thus a living system is determined in different ways by its pattern of organisation and its structure.

The pattern of organisation determines the systems identity (i.e. it's essential characteristics); the structure, formed by a sequence of structural changes, determines the system's behaviour. The behaviour of living systems is "structure determined".

This concept of structural determinism sheds new light on the age-old philosophical debate about freedom and determinism.  The behaviour of a living organism is determined.  However, rather than being determined by outside forces, it is determined by the organism's own structure - the structure formed by a succession of autonomous structural changes.  Thus the behaviour of the living organism is both determined and free.