This book is the narrative of an idea about the control of biological growth that has developed over the course of my career. At an early stage it was given the name Maia, after the Roman goddess of spring, growth and fertility. The origin of the idea goes back to attempts to explain how it could be that toxic agents at low concentrations have the improbable consequence of stimulating growth. Later, perturbation experiments revealed the output of a control mechanism responsible for regulating growth. This breviary of the Maia hypothesis explains the central idea of the book. All that follows derives from the key finding of how to access the output of growth control mechanisms, as ultimately growth must be controlled and constrained. It is one of many homeodynamic processes, all controlled by cybernetic mechanisms. This account is pitched to make the biology accessible to cyberneticists, and the cybernetics accessible to biologists. These preliminary remarks therefore give the crux of the idea, summarising its development, in a few paragraphs, from growth experiments with simple organisms to the point where Maia bears on the two engines of growth on Earth.

During early sensitivity tests of a seawater bioassay with a clonal hydroid (see Frontispiece), it was discovered that low concentrations of toxic agents stimulate biological growth (‘hormesis’).