Evodevo and the promise of understanding morphological transitions in evolution

The field of Evolutionary Developmental biology arose with the promise of new approaches to answering longstanding questions of comparative biology. Here we review the fruits of that promise some decades later. We chose three areas of arthropod EvoDevo-evolution of body plans, segment number, and appendage morphology-to provide an overview for the nonspecialist of how these issues have been clarified by the comparative analysis of regulatory gene networks. In all cases, we identify substantial progress and novel insights provided by the tools and perspective of EvoDevo. We also recognize that some core questions remain unanswered, and we reflect on how discoveries in EvoDevo fit in the landscape of other progress in phylogenetics, population biology, and genomics, facilitated by a new and ever-expanding set of molecular tools for comparative studies in evolution.