From Gaia Hypothesis to Gaia Theory - Animate Earth: Science, Intuition and Gaia - page 51

A system with feedback is one in which a change in one component of the system
propagates around a loop of interrelated components until, eventually the original com-
ponent experiences a change. Feedback loops can be either negative or positive. In a
negative feedback, the initial change is counteracted, whilst in a positive feedback the
initial change is amplified.
First, let's look at a system with simple negative feedback (Figure 7)
Figure 7 * : A system with simple negative feedback.
Here we have only two 'parts' or components that interact, namely hunger and the con-
sumption of food. Systems theorists have worked out a very simple but highly effective
notation for describing feedback that we shall be using throughout this topic in our ex-
plorations of Gaia. Notice that hunger and food consumption are connected with arrows,
which denote couplings. These are of two types: solid and dashed. A solid arrow de-
notes a direct coupling , in which an increase in the component at the tail of the arrow
causes an increase in the component at the tip of the arrow, and vice versa. Conversely, a
dashed arrow denotes an inverse coupling , in which an increase in the component at the
tail of the arrow causes a decrease in the component at the tip, and vice versa (Figure
8) .