Le concept de plan d'organisation : Quelques aspects de son histoire / The concept of Bauplan : Some aspects of its history

Abstract

SUMMARY. — The principle of the subordination of characters, which was inconsistent with the idea of the scala naturae, lead to the Bauplan conception. Cuvier characterized each of his four animal phyla by a particular Bauplan. But how to compare animals which do not possess the same Bauplan ? The contradictory attempts in comparative embryology of von Baer and Geoffroy Saint-Hilaire were reevaluated by Haeckel who proposed six phyla organized along a phytogeny based on embryological characters. He defined five primordial evolutive steps. The following zoologists adopted such a point of view and used characters preceding the Bauplan structuration during embryogenesis. The discovery that numerous developmental genes are conserved across the animal kingdom constitutes the main breakthrough of these last years in evolutionary biology. These genes lead to new phylogenetic characters which are not directly correlated with the Bauplan structuration. They are rather involved in the establishment of the main polarities (antero-posterior and dorso-ventral). One can expect that molecular developmental biology will make it possible to explain by which processes Baupläne were established during evolution make it possible.