Shift happens: The developmental and evolutionary dynamics of the gap gene system

I review a systematic and quantitative comparative study of patterning by the gap gene network during early development in dipteran insects (flies and midges). This work demonstrates the use of reverse-engineering for integrating empirical data with mathematical modeling in order to reconstitute an evolving developmental process in silico. The resulting dynamical models (called gap gene circuits) provide necessary and sufficient mechanistic explanations for pattern formation by this system, and for its compensatory evolution by developmental system drift. Although not structurally modular, I show how the network can be decomposed into overlapping dynamical modules that exhibit differential sensitivity to evolutionary change, explaining the evolvability of the gap gene system.