A complex adaptive system (CAS) is a

system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...

that is ''

complex Complex commonly refers to: * Complexity, the behaviour of a system whose components interact in multiple ways so possible interactions are difficult to describe ** Complex system, a system composed of many components which may interact with each ...

'' in that it is a dynamic network of interactions, but the behavior of the ensemble may not be predictable according to the behavior of the components. It is '' adaptive'' in that the individual and collective behavior mutate and self-organize corresponding to the change-initiating micro-event or collection of events. It is a "complex macroscopic collection" of relatively "similar and partially connected micro-structures" formed in order to adapt to the changing environment and increase their survivability as a macro-structure. The Complex Adaptive Systems approach builds on replicator dynamics. The study of complex adaptive systems, a subset of nonlinear dynamical systems, is an interdisciplinary matter that attempts to blend insights from the natural and social sciences to develop system-level models and insights that allow for heterogeneous agents,

phase transition In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...

, and emergent behavior.

Overview

The term ''complex adaptive systems'', or '' complexity science'', is often used to describe the loosely organized academic field that has grown up around the study of such systems. Complexity science is not a single theory—it encompasses more than one theoretical framework and is interdisciplinary, seeking the answers to some fundamental questions about

living Living or The Living may refer to: Common meanings *Life, a condition that distinguishes organisms from inorganic objects and dead organisms ** Living species, one that is not extinct *Personal life, the course of an individual human's life * ...

, adaptable, changeable systems. Complex adaptive systems may adopt hard or softer approaches. Hard theories use formal language that is precise, tend to see agents as having tangible properties, and usually see objects in a behavioral system that can be manipulated in some way. Softer theories use natural language and narratives that may be imprecise, and agents are subjects having both tangible and intangible properties. Examples of hard complexity theories include complex adaptive systems (CAS) and viability theory, and a class of softer theory is Viable System Theory. Many of the propositional consideration made in hard theory are also of relevance to softer theory. From here on, interest will now center on CAS. The study of CAS focuses on complex, emergent and macroscopic properties of the system. John H. Holland said that CAS "are systems that have a large numbers of components, often called agents, that interact and adapt or learn." Typical examples of complex adaptive systems include: climate; cities; firms; markets; governments; industries; ecosystems; social networks; power grids; animal swarms; traffic flows;

social insect Eusociality (Ancient Greek, Greek 'good' and social) is the highest level of organization of sociality. It is defined by the following characteristics: cooperative Offspring, brood care (including care of offspring from other individuals), ove ...

(e.g.

ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...

) colonies; the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

and the

immune system The immune system is a network of biological systems that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to bacteria, as well as Tumor immunology, cancer cells, Parasitic worm, parasitic ...

; and the cell and the developing

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

. Human social group-based endeavors, such as

political parties A political party is an organization that coordinates candidates to compete in a particular area's elections. It is common for the members of a party to hold similar ideas about politics, and parties may promote specific ideological or p ...

communities A community is a Level of analysis, social unit (a group of people) with a shared socially-significant characteristic, such as place (geography), place, set of Norm (social), norms, culture, religion, values, Convention (norm), customs, or Ide ...

, geopolitical organizations, war, and terrorist networks are also considered CAS. The

internet The Internet (or internet) is the Global network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...

and

cyberspace Cyberspace is an interconnected digital environment. It is a type of virtual world popularized with the rise of the Internet. The term entered popular culture from science fiction and the arts but is now used by technology strategists, security ...

—composed, collaborated, and managed by a complex mix of

human–computer interaction Human–computer interaction (HCI) is the process through which people operate and engage with computer systems. Research in HCI covers the design and the use of computer technology, which focuses on the interfaces between people (users) and comp ...

s, is also regarded as a complex adaptive system. CAS can be hierarchical, but more often exhibit aspects of "self-organization". The term complex adaptive system was coined in 1968 by sociologist Walter F. Buckley who proposed a model of cultural evolution which regards psychological and socio-cultural systems as analogous with biological

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. In the modern context, complex adaptive system is sometimes linked to memetics, or proposed as a reformulation of memetics. Michael D. Cohen and Robert Axelrod however argue the approach is not social Darwinism or

sociobiology Sociobiology is a field of biology that aims to explain social behavior in terms of evolution. It draws from disciplines including psychology, ethology, anthropology, evolution, zoology, archaeology, and population genetics. Within the study of ...

because, even though the concepts of variation, interaction and selection can be applied to modelling '

population Population is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...

s of business strategies', for example, the detailed evolutionary mechanisms are often distinctly unbiological. As such, complex adaptive system is more similar to Richard Dawkins's idea of replicators.

General properties

What distinguishes a complex adaptive system (CAS) from a pure multi-agent system (MAS) is the focus on top-level properties and features like self-similarity,

complexity Complexity characterizes the behavior of a system or model whose components interact in multiple ways and follow local rules, leading to non-linearity, randomness, collective dynamics, hierarchy, and emergence. The term is generally used to c ...

emergence In philosophy, systems theory, science, and art, emergence occurs when a complex entity has properties or behaviors that its parts do not have on their own, and emerge only when they interact in a wider whole. Emergence plays a central rol ...

and

self-organization Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order and disorder, order arises from local interactions between parts of an initially disordered system. The process can be spont ...

. Theorists define an MAS as a system composed of multiple interacting agents; whereas in CAS, the agents as well as the system are adaptive and the system is self-similar. A CAS is a complex, self-similar collectivity of interacting, adaptive agents. Complex adaptive systems feature a high degree of adaptive capacity, giving them resilience in the face of perturbation. Other important properties include adaptation (or

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

), communication, cooperation, specialization, spatial and temporal organization, and reproduction. Such properties can manifest themselves on all levels: cells specialize, adapt and reproduce themselves just like larger organisms do. Communication and cooperation take place on all levels, from the agent- to the system-level. In some cases the forces driving co-operation between agents in such a system can be analyzed using

game theory Game theory is the study of mathematical models of strategic interactions. It has applications in many fields of social science, and is used extensively in economics, logic, systems science and computer science. Initially, game theory addressed ...

Characteristics

Some of the most important characteristics of complex adaptive systems are: * The number of elements is sufficiently large that conventional descriptions (e.g. a system of differential equations) are not only impractical, but cease to assist in understanding the system. Moreover, the elements interact dynamically, and the interactions can be physical or involve the exchange of information. * Such interactions are rich, i.e. any element or sub-system in the system is affected by and affects several other elements or sub-systems. * The interactions are non-linear: small changes in inputs, physical interactions or stimuli can cause large effects or very significant changes in outputs. * Interactions are primarily but not exclusively with immediate neighbours and the nature of the influence is modulated. * Any interaction can feed back onto itself directly or after a number of intervening stages. Such feedback can vary in quality. This is known as ''recurrency.'' * The overall behavior of the system of elements is not predicted by the behavior of the individual elements * Such systems may be open and it may be difficult or impossible to define system boundaries * Complex systems operate under far from equilibrium conditions. There has to be a constant flow of energy to maintain the organization of the system * Agents in the system are adaptive. They update their strategies in response to input from other agents, and the system itself. * Elements in the system may be ignorant of the behaviour of the system as a whole, responding only to the information or physical stimuli available to them locally Robert Axelrod & Michael D. Cohen identify a series of key terms from a modeling perspective: * Strategy, a conditional action pattern that indicates what to do in which circumstances * Artifact, a material resource that has definite location and can respond to the action of agents * Agent, a collection of properties, strategies & capabilities for interacting with artifacts & other agents * Population, a collection of agents, or, in some situations, collections of strategies * System, a larger collection, including one or more populations of agents and possibly also artifacts * Type, all the agents (or strategies) in a population that have some characteristic in common * Variety, the diversity of types within a population or system * Interaction pattern, the recurring regularities of contact among types within a system * Space (physical), location in geographical space & time of agents and artifacts * Space (conceptual), "location" in a set of categories structured so that "nearby" agents will tend to interact * Selection, processes that lead to an increase or decrease in the frequency of various types of agent or strategies * Success criteria or performance measures, a "score" used by an agent or designer in attributing credit in the selection of relatively successful (or unsuccessful) strategies or agents Turner and Baker synthesized the characteristics of complex adaptive systems from the literature and tested these characteristics in the context of creativity and innovation. Each of these eight characteristics had been shown to be present in the creativity and innovative processes: * Path dependent: Systems tend to be sensitive to their initial conditions. The same force might affect systems differently. * Systems have a history: The future behavior of a system depends on its initial starting point and subsequent history. * Non-linearity: React disproportionately to environmental perturbations. Outcomes differ from those of simple systems. * Emergence: Each system's internal dynamics affect its ability to change in a manner that might be quite different from other systems. * Irreducible: Irreversible process transformations cannot be reduced back to its original state. * Adaptive/Adaptability: Systems that are simultaneously ordered and disordered are more adaptable and resilient. * Operates between order and chaos: Adaptive tension emerges from the energy differential between the system and its environment. * Self-organizing: Systems are composed of interdependency, interactions of its parts, and diversity in the system.

Adaptation mechanisms

The organisation of a complex adaptive system rely on the use of internal models, mental models or schemas guiding the behaviors of the system. We can distinguish three levels of adaptation of a system: * Using a schema to react to changing circumstances in the environment.. * Changing a schema when the existing one does not lead to satisfactory outcomes. * Selecting the systems using successfull schemata among a population (

survival of the fittest "Survival of the fittest" is a phrase that originated from Darwinian evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. In Darwinian terms, th ...

Modeling and simulation

CAS are occasionally modeled by means of

agent-based model An agent-based model (ABM) is a computational model for simulating the actions and interactions of autonomous agents (both individual or collective entities such as organizations or groups) in order to understand the behavior of a system and ...

s and complex network-based models. Agent-based models are developed by means of various methods and tools primarily by means of first identifying the different agents inside the model. Another method of developing models for CAS involves developing complex network models by means of using interaction data of various CAS components. In 2013 SpringerOpen/BioMed Central launched an online open-access journal on the topic of ''complex adaptive systems modeling'' (CASM). Publication of the journal ceased in 2020.

Evolution of complexity

Living organisms are complex adaptive systems. Although complexity is hard to quantify in biology,

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

has produced some remarkably complex organisms. This observation has led to the common misconception of evolution being progressive and leading towards what are viewed as "higher organisms". If this were generally true, evolution would possess an active trend towards complexity. As shown below, in this type of process the value of the most common amount of complexity would increase over time. Indeed, some artificial life simulations have suggested that the generation of CAS is an inescapable feature of evolution. However, the idea of a general trend towards complexity in evolution can also be explained through a passive process. This involves an increase in

variance In probability theory and statistics, variance is the expected value of the squared deviation from the mean of a random variable. The standard deviation (SD) is obtained as the square root of the variance. Variance is a measure of dispersion ...

but the most common value, the mode, does not change. Thus, the maximum level of complexity increases over time, but only as an indirect product of there being more organisms in total. This type of random process is also called a bounded

random walk In mathematics, a random walk, sometimes known as a drunkard's walk, is a stochastic process that describes a path that consists of a succession of random steps on some Space (mathematics), mathematical space. An elementary example of a rand ...

. In this hypothesis, the apparent trend towards more complex organisms is an illusion resulting from concentrating on the small number of large, very complex organisms that inhabit the right-hand tail of the complexity distribution and ignoring simpler and much more common organisms. This passive model emphasizes that the overwhelming majority of species are microscopic

prokaryote A prokaryote (; less commonly spelled procaryote) is a unicellular organism, single-celled organism whose cell (biology), cell lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Gree ...

s, which comprise about half the world's

biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...

and constitute the vast majority of Earth's biodiversity. Therefore, simple life remains dominant on Earth, and complex life appears more diverse only because of

sampling bias In statistics, sampling bias is a bias (statistics), bias in which a sample is collected in such a way that some members of the intended statistical population, population have a lower or higher sampling probability than others. It results in a b ...

. If there is a lack of an overall trend towards complexity in biology, this would not preclude the existence of forces driving systems towards complexity in a subset of cases. These minor trends would be balanced by other evolutionary pressures that drive systems towards less complex states.

References

Literature

* *; commissioned as
report
by the UK government'
Foresight Programme
* Dooley, K., ''Complexity in Social Science'' glossary a research training project of the European Commission. * * * * * * * , M.C. (online)
Looking to systems theory for a reductive explanation of phenomenal experience and evolutionary foundations for higher order thought
Retrieved 15 January 2008. * Hobbs, George & Scheepers, Rens (2010),"Agility in Information Systems: Enabling Capabilities for the IT Function," ''Pacific Asia Journal of the Association for Information Systems'': Vol. 2: Iss. 4, Article 2
Link
*

External links

Complex Adaptive Systems Group
loosely coupled group of scientists and software engineers interested in complex adaptive systems
DNA Wales Research Group
Current Research in Organisational change CAS/CES related news and free research data. Also linked to the Business Doctor & BBC documentary series

of complex adaptive systems on the Principia Cybernetica Web.

single-page description of the 'world' of complexity and related ideas hosted by the Center for the Study of Complex Systems at the University of Michigan.
Complex systems research networkThe Open Agent-Based Modeling ConsortiumTEDxRotterdam – Igor Nikolic – Complex adaptive systems
an
The emergence of universal consciousness: Brendan Hughes at TEDxPretoria
Talks discussing various practical examples of complex adaptive systems, including Wikipedia, star galaxies, genetic mutation, and other examples {{DEFAULTSORT:Complex Adaptive System Cybernetics Systems science Complex systems theory Management cybernetics