If morphological diversity is all about development, and development results from genetic regulatory programs, then is the evolution of diversity directly related to the evolution of genetic regulatory programs? Simply put, yes. But to understand how diversity evolves, we must first understand the genetic regulatory mechanisms that operate in development. In other words, what is the genetic toolkit of development and how does it operate to build animals?
In, From DNA to Diversity
Carroll, Grenier and Weatherbee (2001, Blackwell Science; p.13).