Are living organisms, as Descartes argued, just machines? Or is the nature of life such that it can never be fully explained by mechanisitic models? In this thought provoking volume, originally published in hardback in 1987, Elasser argues that the behaviour of living organisms cannot be reduced to physico-chemical causality. Suggesting that molecular biology today is at the same point as Newtonian physics on the eve of the quantum revolution. Elasser lays the foundation for a theoretical biology that points the way toward a natural philosophy of organic life.