Is there any correlation between the number of signalling genes and the diversification of body plans? Does the number of
types of signalling pathway hamper morphological evolution? Is the flexibility of signalling systems sufficient to explain the novelties of body plans? How are new components integrated into existing networks, and how does this change the behaviour of a signalling network? How do signalling systems really evolve at the microevolutionary level, that is, what
type of mutations occur and how are such changes fixed in natural populations? And finally, why do some pathways evolve faster than others? We have reviewed studies that are beginning to provide answers to some of these questions.