• An ant society. There is no “leader” ant. There is no ant with a central plan. But every
ant knows its duty, and this allows their society to act as a whole.
• A flock of birds. Each bird sets its direction in dependence of the direction of its
neighbours. This leads to complex behaviour of the flock. This can also be seen in
schools of fishes, insect swarms, buffalo stampedes, raging crowds, and furious mobs.
Each individual, to decide its action, takes into account the actions of the neighbours.
Other examples of complex systems might be the weather, traffic jams, Mother Web, the
stock market, and an ecosystem.
We suggest the reader to think about natural systems, and think if they’ re complex or
simple. Most of them are complex (otherwise the reader is simple minded???).
A usual mistake is to confuse complexity with complication. A complex system might be
complicated or not, and vice versa. Other usual mistake is to confuse complexity with chaos. A
complex system might also be chaotic or not, and vice versa.
The approach of complex systems allows to understand the behaviour of the system by
understanding the behaviours and interactions of its parts. Studying the system as a whole is
too complicated. And studying only the parts of the system does not allow to understand the
behaviour of the whole system and its emergent properties.
In the last few years, several companies have solved problems in different businesses
using complex systems techniques with very good results (Wakefield, 2001).
2.1.1. Behaviour-based systems as complex systems
BBS might not be complex systems, but adaptive behaviour is indeed a complex system.
Adaptive behaviour in animals (and even in bacteria), requires the interaction of many
components to provide robust perceptions, action selections, and actuations. If adaptive
behaviour would be made out only of simple rules (IF food AND hunger THEN eat), it would
not be capable of adaptation in an unpredictable environment (IF Boeing 757 AND unknown
noise THEN... !). So, a good BBS will be also a complex system. Some properties of a BBS, like
those of an animal, will emerge from the interaction of its components.
2.1.2. Social systems as complex systems
An individual belonging to a society, natural or artificial, might be complex or not. But
in a society, its individuals have to interact (otherwise they would not be social, we would have
just a population). Thus, a society is a complex system (Goldspink, 2000). And social
phenomena emerge from the interactions of the members of a society.
Perhaps the most simple example of this might be given by cellular automata, such as
The Game of Life11 (Conway, 1970; Gershenson, 1997). Each cell is represented by a “life”
11Programs of the Game of Life, in two dimensions (using boolean, fuzzy, and multidimensional
(Gershenson, 1998a; Gershenson, 1999) logics) and in three dimensions with source code can be found at
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