• 1 Laboratoire d'Applications des Systèmes Tychastiques Régulés

This article deals with a theme to which Claude Lobry has been interested for a long time: what is the nature of mathematics motivated by biological sciences? It starts by presenting the subjective opinions of its author, illustrated by the simplest application one can think of: demonstrating that it is possible to produce cyclic evolutions on the simple basis of viability and inertia constraints, without using periodic differential equations. It is not impossible that this approach is foreign to an explanation of biological clocks (or economic cycles) in another field.