In this talk, I would like to contrast some of my findings on gene network evolution and then place them in a single framework. First, evolution may mean rapid adaptation, or being evolvable. It has been observed both in nature and in the lab, and it has puzzled biologists. Can evolvability be selected for? Inspired by experimental evolution on yeast, I studied network evolution in changing environments. Using computer simulations, I found that network structure evolves to allow for rapid adaptation. A clear example of the evolution of evolvability, that neatly demonstrates how function and evolution are intertwined. Second, evolution may mean robustness, or an apparent lack of change. Together with experimental biologists, I studied the evolution of the gap gene network, which is involved in body plan patterning of the fruit fly Drosophila and the scuttle fly Megaselia. Both flies have differences in upstream factors and gap gene expression dynamics, while the final gap gene patterns are virtually identical. With a detailed analysis of gap gene regulation, I show how the flies compensate for species-specific differences. We named the phenomenon "quantitative system drift" and suggested it is a common mode of evolution in development. Finally, I discuss how both studies may be understood in the framework of "evolving on a genotype network".
