// The Song Remains The Same

(Part of a continuing series, “The Principles of Self Organization”; Emergence was the first article and the article on Positive Feedback precedes this article.)

Feedback is a mechanism in any system to describe how well something performs, from report cards, to profit and loss statements — feedback lets us know where we stand in relation to a system.

Positive Feedback, as we saw in the previous section, was a technique used to amplify patterns and create patterns. Negative feedback is what we employ in order to keep these patterns and positive feedback under control.

A interesting example of feedback in action is the schooling behavior exhibited by groups of fish. The basic algorithm deduced from this behavior is that each fish adjusts its vector towards its local neighbors at each “time step”, and if the fish strays too far from the school it then hurries to move closer to the group. In the book “Self Organization In Biological Systems” the schooling or “flocking” effect is stated to result from the balance between attraction and repulsion. This attraction and repulsion is driven by local stimuli such as vision and touch/pores.

If the fish gets too close to a neighbor, then it backs off some. If it gets too far away, it moves towards the group (this is a highly simplified version of the algorithm for the purposes of this example). Both of these adjustment mechanics are examples of negative feedback as the individual fish judged its position to be non-optimal, which created the negative feedback, which in turn prompted an adjustment of its position. In this particular example we did not demonstrate positive feedback; however, I simply wanted to isolate and talk about how negative feedback can keep a “process” under control and in order. Now that we’ve seen a basic example of negative feedback, let’s take a look at another example that demonstrates negative and positive feedback in play together.

The nature of positive feedback implies that it has the potential to cause large scale and unwieldy implosions or explosions in the pattern where it plays a role. Negative feedback is the mechanism by which we keep positive feedback and amplification under control. Population growth and dynamics are an interesting example in the interplay of positive and negative feedback:

• As more people are born, more people have children, which creates the positive feedback loop. The basic building block of the process, here people, increases, which accelerates the yield of the process.
• After a period of time, competition for resources increase to the point where it becomes more difficult for a population to thrive, so it creates a “drag” effect on the individual’s ability to thrive.  Overcrowding in human populations is a type of negative feedback that tends to scale back population booms as competition for limited resources increases which reduces the amount of basic building blocks for the process.

In order to find a stable state, self organizing biological processes need both negative and positive feedback. Without both of them, the process either grows out of control (no negative feedback) resulting in destruction (cancer) or no process starts at all (no positive feedback).

With self organization we have to manage both the growth and control phases of a process. The key thing to know about negative feedback is that it is a technique of control in large populations of interacting agents or units, such as ants in a colony or atoms in a molecule. In coming articles, I want to take a look at where else these complimentary mechanics, positive and negative feedback, are applicable in the business, technological, and algorithmic worlds. However, before we can get there, I’d like to take a look at the other driver in self organization: “stigmergy”.