Chapter 5

What happens when balancing forces interact? What emerges when we have interaction between individuals all striving for some type of balance? Here’s a simple example: When an individual feels a need, he takes action to satisfy. If hungry then eat. Such individual behavior can maintain physiological balance. However, suppose the perceived need also spreads socially. An individual’s perceived need increases every time he sees another person satisfying his own need, e.g., when he eats candy. We can represent individuals as squares on a checkerboard and their level of perceived need as a stack of quarters, ranging from no quarters, representing zero perceived need, to four quarters, a perceived need high enough to trigger action. Imagine any single individual starts to build up a perceived need, perhaps because they are susceptible to advertisements for candy. Add quarters one by one to this individual’s square representing the individual’s perceived need for the candy. The candy costs a dollar, and the number of quarters on the stack represents the level of their perceived need, their willingness to pay for the candy. Once the need reaches four quarters worth, the individual buys and consumes the candy, satisfying their hunger and so reducing the perceived need back down to zero (we remove their quarters). This action (consumption of candy) is visible to the four neighbors, left, right, above and below on the checkerboard. Every time neighbors see an action, their own perceived need builds up, which we represent by adding another quarter. Once an individual sees the behavior four times, either from the same individual over time or from several neighbors, their need for the candy reaches the threshold necessary to act. We will explore many variants and complications including the metabolic balancing and reward circuitry involved in wanting sugary foods. But we need to understand simple components of the model fully, taking the time to observe any complexity that might emerge. Do we understand this very simple model well enough to predict what will happen? Our individuals are following two simple conditional action rules, need buildup (IF neighbor takes action THEN add 1 to my perceived need) and need satisfaction (IF my need reaches 4 THEN take action, reducing my perceived need to 0). All we do, as outside experimenters, is stimulate the need of one person, adding quarters one by one to an individual’s patch (or to several randomly distributed individuals). This outside influence represents some stimulation of need other than imitation, perhaps the influence of media. We have all the individuals follow the above two rules, over and over. This model may seem too simple to be useful, but do we know what will happen? What will the collective behavior be over time? The results turn out to be a good example of a complex system, one generating a great diversity of collective behaviors. We will review this and several variants later in this book, but here I use it to point out the surprising collective complexity emerging from simple rules. The collective behavior starts out looking like a linear increase in the number of persons eating candy, but suddenly we will see an explosion of simultaneous behavior, an avalanche of candy eating, with great numbers of individuals suddenly eating candy all at once. We then see behavioral explosions of all sizes, very small and large avalanches of candy eating. From one day to the next day, we see dramatically different distributions of behaviors, a great diversity of numbers of individuals engaging at any given time, and also a great diversity of patterns of social networks.