Exploring evolutionary constraints is a task for an integrative evolutionary biology

Judging by the volume of writings about evolutionary constraints, they are an important topic in evolutionary biology. However, their involvement in shaping patterns of evolutionary change from morphological stasis to adaptive radiation remains contentious. This is at least in part because of the paucity of robust analyses of potential examples of constraints, whether of a more absolute or a relative nature. Here, we argue that what is needed to explore the type of constraints and bias on evolutionary change that may emerge from the way in which phenotypic variation is generated is an integrative approach applied to systems that can be tackled at different levels of biological organization. This is illustrated using research on the evolution of patterns in butterfly wing eyespots that has applied a combination of evolutionary genetics and evo-devo to an emerging model species with the beginnings of a comparative approach to describe patterns of variability among the extant taxa of two species-rich genera.