Snail shell coiling (re-)evolution and the evo-devo revolution

During the last two decades evolutionary developmental biology has become a major research programme whose findings put into question some concepts lying at the core of the ‘Synthetic Theory’. However, some authors are waiting for a ‘revolution’ in biology, one in which the existing genetic determinism will give way to a new conceptual understanding of the complexity of living organisms. This ‘revolution’ should necessarily pass through the elaboration of an appropriate theoretical framework integrating the non‐linear dynamics of development as its fundamental basis. This objective implies a drastic shift in the way causality is generally understood as well as a purge of numerous convenient but misleading metaphors such as genetic or developmental programmes. Although most authors do not take these metaphors too literally, some persist in employing such ‘instructionist’ notions in a more literal perspective, and, in doing so, deny some concepts at the core of evolutionary developmental biology. We critically review two recent studies suggesting that shell coiling has re‐evolved in a family of limpets (Calyptraeidae, Gastropoda). We stress that this putative re‐evolution of snail shell coiling results only from an arbitrary scoring procedure leading us to consider shell coiling as a binary discrete character. We show that the way in which these authors connect this case study to evolutionary theories stems from the unwarranted premise of a linear mapping of genes onto phenotypes where particulate inheritance of morphological characters seems implicitly assumed. We illustrate how the persisting unclear role of genes in morphogenesis allows the maintenance of the adaptationist programme. Résumé Ces vingt dernières années, l'evo‐devo (biologie évolutive du développement) est devenue un programme de recherche florissant remettant en cause certains concepts centraux de la ‘Théorie Synthétique’. Cependant, certains auteurs attendent une ‘révolution’ en biologie par laquelle le déterminisme génétique encore en vigueur cèdera la place à une nouvelle perception de la complexité des organismes vivants. Cette ‘révolution’ requiert l’élaboration d’un cadre théorique approprié intégrant comme base fondamentale la dynamique non linéaire du développement. Cet objectif implique une profonde modification de la façon dont la causalité est généralement comprise de même que l'abandon de commodes mais trompeuses métaphores, telle que celle de programme génétique ou développemen