
3
Nonlinear systems
3.1 Introduction
Nonlinearity appears to be a fundamental property o f biological systems. One
reason for this may be the inherent complexity of biology — in the physical
world, linear equations such as Newton’s, Ma xwell’s and Schroedinger’s are
immensely successful descriptions of reality, but they are essentially equations
of forces in a vacuum. Nonlinear ity is fundamental in generating qualitative
structural changes in complex phenomenon such as the transition from laminar
to turbulent flow, or in phase changes from gas to liquid to solid. Whenever
there are phase changes, whenever structure ar ises, nonlinear dynamics are
often ...