To what extent are we determined by our genes? Can we hope that gene therapy will put an end to all our ills? Will the manipulation of genes lead to the degradation of human beings and a most uncertain future?How can these questions be broached if the human genome remains unintelligible -- even after its mystery has been unravelled -- and can only be described as containing a series of characteristics whose meaning is obscure? In an effort to understand the paradox of genetics -- a science which is simultaneously all-powerful and empty of meaning -- the author examines the importance of the subject throughout history, while questioning its role as a fundamental science. The issues that must be addressed can be summarised by the following questions: What is more important in order to bake a good cake: the cake tin or the actual cooking process? What is of greater significance to understand life: genes or proteins? Michel Morange teaches at the University of Paris-VI and heads a research team on the molecular biology of stress at the Ecole Normale Supérieure.