The evolutionary analysis of animal development
is still at its beginning and, therefore, there are more
open questions than solid answers. With several case
studies on their way, the emergence of general patterns
is, however, only a question of time. The conservation
of signalling pathways was only established as a
general concept after developmental processes had
been studied in flies, worms and vertebrates. In a similar
way, general principles in evolutionary developmental
biology will emerge after a sophisticated
analysis of several case studies has been carried out in
selected animals.