Fig. 5

Selection only for tissue size occasionally yields anterior or posterior growth (transient signal, CCS). Examples of individuals which evolved anterior growth (a), posterior growth (c) or a combination of the two (b) in the absence of selection for segments (as described in the main text). a Anterior growth exploits the fact that the head does not express gene 0 (morphogen) and does not divide; therefore, it accumulates division protein (4). The head thus functions as a signalling centre. c Posterior growth uses the fact that the posterior-most cell has only one neighbouring cell and thus receives less cell–cell signalling. In the networks, the signalling genes 1 and 2 are circled in yellow and the division gene in magenta