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Emergence is the process of deriving some new and coherent structures, patterns and properties in a complex system. Emergent phenomena occur due to the pattern of interactions between the elements of a system over time. Emergent phenomena are often unexpected, nontrivial results of relatively simple interactions of relatively simple components. What distinguishes a complex system from a merely complicated one is that in a complex system, some behaviours and patterns emerge as a result of the patterns of relationship between the elements.


Emergent properties

An emergent behaviour or emergent property is shown when a number of simple entities (agents) operate in an environment, forming more complex behaviours as a collective. A system made of several things can host and exhibit properties which the things themselves do not have. For instance, consider two points on a plane. These points will have a distance between them. This distance is not itself a property, but exists in the relation between the points. If we have more than two points, we can for example define a density. Emergent properties can arise not only between things in the system, but between other emergent properties. The number and subtlety of these properties can be very much greater than the number of things.

Emergent properties arise when a complex system reaches a combined threshold of diversity, organisation, and connectivity. The property itself is often unpredictable and unprecedented, and represents a new level of the system's evolution. The complex behaviour or properties are not a property of any single such entity, nor can they easily be predicted or deduced from behaviour in the lower-level entities. The shape and behaviour of a flock of birds or school of fish are good examples.

Systems with emergent properties or emergent structures may appear to defy entropic principles and the second law of thermodynamics, because they form and increase order despite the lack of command and central control. This is possible because open systems can extract information and order out of the environment.

Emergence helps to explain why, for instance, the number of ways of packing boxes into a truck increases exponentially with the number of boxes and why the fallacy of division is a fallacy. According to an emergent perspective, intelligence emerges from the connections between neurons, and from this perspective it is not necessary to propose a "soul" to account for the fact that brains can be intelligent, even though the individual neurons of which they are made are not.

Emergent behavior is also important in games and game design. For example, the game of poker, especially in no limit forms without a rigid betting structure, is largely driven by emergent behavior. For example, no rule requires that any player should fold, but usually many players do. Because the game is driven by emergent behavior, play at one poker table might be radically different from that at another, while the rules of the game are exactly the same. Variations of games that develop are examples of emergent metaplay, the predominant catalyst of the evolution of new games.

Emergent structures in Nature

Emergent structures are patterns not created by a single event or rule. There is nothing that commands the system to form a pattern, but instead the interactions of each part to its immediate surroundings causes a complex process which leads to order. One might conclude that emergent structures are more than the sum of their parts because the emergent order will not arise if the various parts are simply coexisting; the interaction of these parts is central.

A biological example is an ant colony. The queen does not give direct orders and does not tell the ants what to do. Instead, each ant reacts to stimuli in the form of chemical scent from larvae, other ants, intruders, food and build up of waste, and leaves behind a chemical trail, which, in turn, provides a stimulus to other ants. Here each ant is an autonomous unit that reacts depending only on its local environment and the genetically encoded rules for its variety of ant. Despite the lack of centralized decision making, ant colonies exhibit complex behavior and have even been able to demonstrate the ability to solve geometric problems. For example, the ant colonies routinely find the maximum distance from all colony entrances to dispose dead bodies.

Besides emergence in ant colonies, which is like other emergent structures in social insects mainly based on pheromones and chemical scents, emergence can be observed in swarms and flocks. Flocking is a well-known behavior in many animal species from swarming locusts to fish and birds. Emergent structures are a favorite strategy found in many animal groups: colonies of ants, piles of termites, swarms of bees, flocks of birds, herds of mammals, shoals/schools of fish, and packs of wolves.

Emergent structures can be found in many natural phenomena, from the physical to the biological domain. The spatial structure and shape of galaxies is an emergent property, which characterizes the large-scale distribution of energy and matter in the universe. Weather phenomena with a similar form such as hurricanes are emergent properties, too. Many speculate that consciousness and life itself are emergent properties of a network of many interacting neurons and living cells, respectively.

Emergent systems in Culture and Engineering

Emergent processes or behaviours can be seen in many places, from any multicellular biological organism to traffic patterns, cities or organizational phenomena in computer simulations and cellular automata. The stock market is an example of emergence on a grand scale. As a whole it precisely regulates the relative prices of companies across the world, yet it has no leader; there is no one entity which controls the workings of the entire market. Each agent, or investor, has knowledge of only a limited number of companies within their portfolio, and must follow the regulatory rules of the market. Through the interactions of individual investors the complexity of the stock market as a whole emerges.

Popular examples for emergence are Linux and other open source projects, the World Wide Web (WWW) and Wikipedia itself. Emergence is besides the efforts of the Wikipedia founders Jim Wales and Larry Sanger the major reason for the appearance and the success of Wikipedia . All of these decentralized and distributed projects are not possible without a huge number of participants and volunteers. No participant alone knows the whole structure, everyone knows and edits only a part, although everybody has the feeling to participate in something big. The top-down feedback increases motivation and unity, the bottom-up contributions increase variety and diversity. This unity in diversity causes the complexity of emergent structures.

Emergent structures appear at many different levels of organization. Emergent self-organization appears frequently in cities where no planning or zoning entity predetermined the layout of the city. The interdisciplinary study of emergent behaviours is not generally considered a homogeneous field, but divided across its application or problem domains.

Emergence in physics

In physics, emergence is used to describe a phenomenon which occurs at macroscopic scales but not at microscopic scales, despite the fact that a macroscopic system can be viewed as a very large ensemble of microscopic systems. Some examples include:

  1. Temperature. Individual particles can have energy, momentum, and velocity, but not temperature. Temperature only emerges when considering an ensemble of particles large enough for the laws of thermodynamics to apply. Similarly, elementary particles (or atoms) do not exist in separate solid, liquid, or gaseous states; these concepts only emerge above the atomic scale.
  2. Color. Elementary particles such as protons or electrons have no color; it is only when they are arranged in atoms that they absorb or emit specific wavelengths of light and thus be said to have a color. (Note that while quarks have a characteristic which has been labeled color charge by physicists, this terminology is merely figurative and has no actual relation with the everyday concept of color).
  3. Friction. Elementary particles are frictionless, or more precisely the forces between these particles are conservative. However, friction emerges when considering more complex structures of matter, whose surfaces can absorb energy when rubbed against each other. Similar considerations apply to other emergent concepts in continuum mechanics such as viscosity, elasticity, tensile strength, etc.

In some theories of particle physics, even such basic structures as mass, space, and time are viewed as emergent phenomena, arising from more fundamental concepts such as the Higgs boson or strings. In some interpretations of quantum mechanics, the perception of a deterministic reality, in which all objects have a definite position, momentum, and so forth, is actually an emergent phenomenon, with the true state of matter being described instead by a wavefunction which need not have a single position or momentum.

It should be emphasized that in each of these cases, while an emergent phenomenon at the macroscopic scale does not directly exist at the microscopic scale, its existence at macroscopic scales can still be explained (perhaps after a substantial amount of rigorous or semi-rigorous mathematical analysis) by the laws of physics at microscopic scales, taking into account the interactions between all the microscopic components of a macroscopic object. Thus, emergent phenomena can demonstrate why a reductionistic physical theory, viewing all matter in terms of its component parts, which in turn obey a relatively small number of laws, can hope to model complex objects such as living beings. However, by the same token, emergent phenomena serve to caution against greedy reductionism, because the microscopic explanation of an emergent phenomenon may be too complicated or "low-level" to be of any practical use. For instance, if chemistry is explainable as emergent from interactions in particle physics, cell biology as emergent from interactions in chemistry, humans as emergent from interactions in cell biology, civilizations as emergent from interactions of humans, and human history as emergent from interactions between civilizations, this does not imply that it is particularly easy or desirable to try to explain human history in terms of the laws of particle physics. (This has not dissuaded some people from hypothesizing that highly complex, emergent phenomena such as human history can be described in terms of simpler laws which are more commonly associated to more fundamental theories. See for instance the theory of Kondratiev waves, or the fictional science of psychohistory.)

Emergence in evolution

Although the principle of emergence is appealing and fascinating, it is not the only reason for the sudden appearance of complexity. There are many reasons for the slow or sudden appearance of complexity. If something emerges very suddenly or fast, it has for instance often been blocked before by an obstacle or barrier, e.g. a jam, a dogma, or barrier or a system border.

Life is certainly the major source of complexity, and evolution is the major principle or driving force behind life. Evolution is the main reason for the growth of complexity. There are sometimes sudden jumps in evolution - it is not a continuous, steady process - but the classic principle of emergence is not the only explanation for these jumps. Very complex systems of extraordinary complexity have usually evolved over a very long time, they do not appear over night. Large, sudden jumps have good causes.

Evolutionary transitions. Large jumps in complexity are related to evolutionary transitions, sudden leaps to new levels of complexity and organization. Transitions to new replicators. Very large jumps in complexity and huge evolutionary transitions are related to the emergence of new replicators (genes, memes, ...) and completely new forms of evolution (biological, cultural, ...).

The different levels of complexity and organization in organisms are separated by evolutionary transitions and large fitness gaps/barriers. Abrupt, unsteady changes and jumps in complexity are the consequence of unsteady fitness landscapes and barriers. Evolution waits until major events like massive catastophes break these fitness barriers or agents are able to tunnel through them.

See also


  • Harold J. Morowitz, The Emergence of Everything: How the World Became Complex (2002) Oxford University Press, ISBN 019513513X
  • Armand Delsemme, Our Cosmic Origins: From the Big Bang to the Emergence of Life and Intelligence (1998) Cambridge University Press
  • John Maynard Smith and Eörs Szathmáry, The Major Transitions in Evolution (1997) Oxford University Press, ISBN 019850294X

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Last updated: 10-15-2005 03:30:34
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