
5
Positive feedback systems
5.1 Introduction
As seen in the previous chapter, negative feedback contro l loops play an im-
portant role in enabling many different types of biological functionality, from
homeostasis to chemotaxis. When evolutionary press ures c ause negative feed-
back to be supplemented with or replaced by positive feedback, other dynami-
cal behaviours can be produced which have been used by biological systems for
a variety of purposes, including the generation of hysteretic switches and oscil-
lations, and the suppression of noise. Indeed, it has recently been argued that
intrac ellular regulatory networks co ntain far more po sitive ...