It is frequently said that biology is emerging from a long phase of reductionism. It would be certainly more correct to say that biologists are abandoning a certain form of reductionism. We describe this past form, and the experiments which challenged the previous vision. To face the difficulties which were met, biologists use a series of concepts and metaphors - pleiotropy, tinkering, epigenetics - the ambiguity of which masks the difficulties, instead of solving them. In a similar way, the word “post-genomics” has different meanings, depending upon who uses it. Which of these meanings will become dominant in the future is an open question.