Abstract : We highlight the double nature of the relationships between economics and biology, which leads to a double appreciation of these interdisciplinary exchanges. On the one hand, some economists perceived their work as consisting primarily in the development of a research method (a « constitutive metaphor ») rather than of a definite subject matter. Disciplinary frontiers appeared then to be relatively arbitrary and analogies between economic and biological models meant that the metaphor had a wide reach. On the other hand, a number of economists were interested in biology because it supplied concepts that were useful to advance the understanding of pre-identified economic problems. Interdisciplinary relations were valued according to this criterion and contacts with biologists were not further pursued. This weaker link between economics and biology led to more fruitful results, because of its intradisciplinary foundations in problems with a more obvious empirical dimension.