Saturday, October 31, 2009

Key Concept: Emergence or Those flocking boids!

One of the great philosophical arguments of all time involves conceptualizing the relationship between different levels of phenomena: does one favor organicism or reductionism? Is the whole greater than the sum of its parts? Or can it be reduced to an understanding of those parts?

Sociology, following Durkheim and his 'social facts can only be explained through reference to other social facts' dictum, traditionally favored organicism. One of the more interesting places to explore these ideas is by looking at emergence. How, for example, do we understand the flocking of birds or the existence of segregated neighborhoods in cities?

Craig Reynolds has a mesmerizing page where you can watch an individual based model of boids that mimic the flocking behaviour of birds. In philosophical terms, Reynolds is trying to explain the emergent phenomena of flocking behaviour through a set of individual-level instructions to his computerized agents (the boids). The page does an excellent job of explaining both the assumptions that are programed into the agents and providing links to a wide variety of relevant literature.

This is similar to the famous explanation for segregation provided by Nobel prize winning economist Thomas Schelling in his book Micromotives and Macrobehavior. By positing the existence of individuals (agents in the jargon) with slight-but-not-malicious preference to have neighbors of the same race, Schelling developed an agent based model showing that, over time, the result of people acting to meet these preference leads not to a mixed neighborhood but, rather, to completely segregated populations. There are a number of different simulations of this on the web, for example, here, here and here. A simpler and less interesting version is here.

But, as Russ Abbott has noted, while boids do a good job of modeling flocking behavior, they ignore energy issues. Thus, as currently conceived, most agent based representations of ecosystem phenomena are seriously deficient.

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