Interactions between elements may form loops. When A impacts B, while at the same
time B impacts A, we say that there is a feedback in the system. Sometimes these loops
are not that obvious and may involve several elements: A → B → C → D → A.
When describing flows in a system it is useful to identify stimulating or a damping
effects. For example, consider a process of population growth. The larger the number
of individuals in a population, the more potential births are occurring, the larger the
number of individuals in a population, etc. This is an example of a positive feedback.
On the contrary, a system with negative feedback tries to stabilize itself according to
negative feedback the rule: the larger something is—the smaller something becomes.
Systems with positive feedback end up in uncontrolled exponential growth or collapse.
Systems with negative feedback tend to stabilize at a certain level.
Positive feedback
There are numerous examples of systems with a positive feedback. When a student
learns to read, the better she can read the more books she starts to read, the better she
learns to read. Or another one: The more the weight of a person, the less fun it is for
him to walk, the less he enjoys hiking or going somewhere, the less he burns calories,
the more he gains weight. And so on.
Negative feedback
A typical example is the one with populations: if there is a limited supply of food, and the population grows, there is less food for each individual. The more the population grows, the less food there is for each organism. At some point there is not enough food to support the
population and some individuals die. Eventually growth shuts down completely, and
the population equilibrates at a level that can be sustained by the supply of food.