CAS Defining Features

Complex adaptive systems are defined according to a variety of characteristics that are consistent regardless of the system.

While various researchers have sought to identify ‘principle’ components of Complex Adaptive Systems, these defining features vary with no ‘authoritative’ definition in place. Surveying CAS, Philosopher Paul Cilliers remarks, ‘the concept remains elusive at both the qualitative and quantitative levels’. Francis Heylighen echoes this sentiment, stating:

'Qualitative descriptions can be short and vague, such as ‘complexity is situated in between order and disorder’. More commonly, authors trying to characterize complex systems just provide extensive lists or tables of properties that complex systems have and that distinguish them from simple system. These include items such as: many components or agents, local interactions, non-linear dynamics, emergent properties, self-organization, multiple feedback loops, multiple levels, adapting to its environment, etc. The problem here of course is that the different lists partly overlap, partly differ, and that there is no agreement on what should be included.'

These disagreements result in considerable ambiguities in how concepts are discussed.  Different discourses engaging CAS often employ descriptors that, while intending to describe the same features, are generally not agreed upon. Hence, terms including Manifold, Phase Space, ‘space of possibility’, and The Virtual all essentially refer to the same thing. Crucially, even principle terms such as Emergence and self-organization remain subject to debate. The word ‘complexity’ itself is often conflated with the word ‘complicated’. Meanwhile, some researchers qualify CAS according to governing mechanisms, distinguishing between algorithmic, deterministic, and aggregate complexity. Others use terminology in metaphoric ways – where any decisions become ‘Bifurcations’ point, regardless of whether or not this is a threshold associated with a relevant control parameter. The ever-increasing array of terms and concepts makes it increasingly difficult to gain insights across discourses. 

The phrase  ‘Complex Adaptive System’ itself has an ambiguous history. In 1967, Sociologist Walter Buckley, informed by systems and cybernetic approaches, introduced the phrase to discuss aspects of the personality. However, the use of the term ‘adaptive’ is deceptive, as it was not intended to describe the nature of the system itself, but rather act as a qualifier on its human element - a cognitive subject possessing ‘adaptive capacity’. By contrast, as early as 1962 Herbert Simon described systems one would now call CAS, but while he speaks both of ‘complex systems’ and their ‘adaptiveness’ he does not employ the phrase nor offer a definition of what such systems would entail.

CAS as understood today can be traced back to the mid-1980s at the newly formed Santa Fe Institute. In the summer of 1986, the Institute announced a workshop on ‘Complex Adaptive Systems’ described as, ‘systems comprising large numbers of coupled elements the properties of which are modifiable as a result of environmental interactions’Both John Holland and Murray Gell-Mann adopt this usage by the mid-1980s, but no mention of its meaning seems to be circulated until the early 1990s - at which point various definitions of CAS appear outlining its ‘principles’, ‘attributes’ or ‘defining features’.

Of the definitions circulated since that time, I have chosen eleven highly cited references to compare, (which can be viewed on the home page). While specific terminology amongst these differ (and there is a lack of consistency regarding which CAS aspects are highlighted), there nonetheless remains a great deal of overlap between the respective traits when considered as a group. The general defining traits surmised from this literature review suggest CAS to be:

- adaptive, evolutionary, and rule-based;

- comprised of a variety of agents;

- described by scale-free/nested mathematical hierarchies; 

- characterized by self-organizing and emergent global properties;

- organized by flows and interactions; and

- subject to non-linear and historical processes.


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