How Do Developmental Programs Evolve

Since the observation made by Karl Ernst von Baer that general anatomical characters of the large taxonomic group, to which an embryo belongs, appear earlier in development than the more special characters, scientists realized that morphologies are the result of changes in development. However, changes in development are potentially dangerous, and the more pronounced they are the more likely it is that the animal, if viable at all, will not be able to pass the filter of selection. In this chapter, I discuss some of the things we learnt in the recent years about how developmental programs can change and give rise to new morphologies without destroying the organisms in which they are deployed.