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Object Interactions
We have now arrived at the first line of Holland's quote: "Emergence is above all a product of coupled, context-dependent interactions." So far we have looked at the general kinds of emergence that can come out of a system. But what is it about a system that allows it to cross the complexity barrier and become truly emergent? The key is in the terms "coupled" and "context-dependent." When Holland says that emergence is a product of these two forms of interaction, he means interactions between objects within a system. Recall from Systems Littlejohn's four elements of a system: objects, attributes, internal relationships, and environment. When the rules of an emergent system are set into motion, the internal relationships between the objects begin to transform the attributes of the elements. These transformations then affect change in the objects' internal relationships, further altering their attributes, resulting in loops and patterns of behavior. Thus, the interactions of a complex system are coupled, meaning that the elements of the system are linked recursively. Like ants in a colony, the objects in the system act together to perform in ways that single objects cannot. Because the objects are linked to each other, one change in the system creates another change, which creates another change, giving rise to patterns over the space of the system. These interactions are context-dependent, which means that the changes that occur are not the same every time. Instead, the exact nature of the transformations depends on what else is happening in the system at any given moment. Coupled interactions help produce global patterns across a system; context-dependent interactions ensure that the exact arrangement of these patterns are dynamically changing over time.
In the messenger communication system example, the objects (messengers and buildings) have attributes and also have relationships to each other. If a messenger picks up mail from a building, the attributes of the building (Does it have undelivered mail or not?) and the attributes of the messenger (Does the messenger have mail to deliver? What is the next destination?) change as a result. As the system runs, the objects of the system interact with each other in ways determined by the rules of the system. If the system were truly emergent, unexpected patterns would arise in the behaviors of the objects, behaviors not contained in the rules themselves. For example, imagine that we decided to color blue any building that didn't have any messages waiting to be picked up. It could be that patterns of blue buildings would cycle regularly lengthwise across the system. These patterns are not part of any of the sys-tem's rules but are patterns that nevertheless arise out of the system as it functions. This is precisely the kind of emergent pattern that Steven Johnson described in his fanciful example of motorized billiard balls in the quote at the beginning of this chapter. In both cases, the coupled, context-dependent interactions among elements of the system are responsible for the emergent phenomena.
