Complex adaptive systems, are a special case of complex systems. They are 'complex' in that they are diverse and made up of multiple interconnected elements and 'adaptive' in that they have the capacity to change and learn from experience. The name complex adaptive systems has been coined at the interdisciplinary Santa Fe Institute (SFI), by John H. Holland , Murray Gell-Mann and others. John H. Holland is one of the inventors of evolutionary computation and genetic algorithms, Nobel Prize laureate Murray Gell-Mann discovered quarks.

The term complex adaptive systems (also complexity science) is often used to describe the loose academic field that has grown up around the study of complex adaptive systems. Complexity science is not a single theory - it encompasses more than one theoretical framework and is highly interdisciplinary, seeking the answers to some fundamental questions about living, adaptable, changeable systems.

Examples of complex adaptive systems include the stock market, social insect and ant colonies, the biosphere and the ecosystem, the brain and the immune system, the cell and the developing embryo, manufacturing businesses and any social human group-based endeavour in a cultural and social system such as political parties or communities. There are close connections between the field of CAS and artificial life. In both areas the principles emergence and self-organization are very important.

Definitions

A CAS is a complex, self-similar collectivity of interacting adaptive agents. The study of CAS focus on complex, emergent and macroscopic properties of the system. Various definitions have been offered by different researchers:

• John H. Holland

A Complex Adaptive System (CAS) is a dynamic network of many agents (which may represent cells, species, individuals, firms, nations) acting in parallel, constantly acting and reacting to what the other agents are doing. The control of a CAS tends to be highly dispersed and decentralized. If there is to be any coherent behavior in the system, it has to arise from competition and cooperation among the agents themselves. The overall bevehavior of the system is the result of a huge number of decisions made every moment by many individual agents. (Source: M. Waldrop's book about "Complexity: The Emerging Science at the Edge of Order and Chaos")

• Kevin Dooley

A CAS behaves/evolves according to three key principles: order is emergent as opposed to predetermined (c.f. Neural Networks), the system's history is irreversible, and the system's future is often unpredictable. The basic building blocks of the CAS are agents. Agents scan their environment and develop schema representing interpretive and action rules. These schema are subject to change and evolution. (Source: K. Dooley, AZ State University)

• Other definitions

Macroscopic collections of simple (and typically nonlinearly) interacting units that are endowed with the ability to evolve and adapt to a changing environment. (Source [1])

Properties of CAS

What distinguishes a CAS from a pure MAS is the focus on top-level properties and features like self-similarity, complexity, emergence and self-organization. A multi-agent system (MAS) is simply defined as a system composed of multiple, interacting agents. In CASs, the agents as well as the system are adaptive: the system is self-similar. A CAS is a complex, self-similar collectivity of interacting adaptive agents.

Other important properties are adaptation (sometimes also named homeostasis), communication, cooperation, specialization, spatial and temporal Organization, and of course reproduction. They can be found on all levels: cells specialize, adapt and reproduce themselves just like larger organisms do. Communication, Cooperation takes place on all levels, from the agent to the system level.

Researchers and scientists

• Prof. Ozalp Babaoglu, University of Bologna
• Prof. Stephanie Forrest, University of New Mexico
• Prof. Melanie Mitchell, Portland State University

See also

• Santa Fe Institute

External links

• CAS Group at Iowa State University
• CAS Research Site by Mark Voss
• Plexus Institute - An organization dedicated to bringing the benefits of complex adaptive systems to the world
• Santa Fe Institute - The Santa Fe Institute is devoted to creating a new kind of scientific research community, one emphasizing multidisciplinary collaboration in pursuit of understanding the common themes that arise in natural, artificial, and social systems. This unique scientific enterprise attempts to uncover the mechanisms that underlie the deep simplicity present in our complex world.
• A description of complex adaptive systems on the Principia Cybernetica Web (a project that aims to develop a complete philosophy or worldview, based on the principles of evolutionary cybernetics, and supported by collaborative computer technologies)
• [2] - A quick reference single-page description of the 'world' of complexity and related notions..hosted by The Center for the Study of Complex Systems at the University of Michigan.
• Yahoo! CAS Group
• RedFish Group