Fig. 1

Overview of the model. a The developing individuals live on a 2D lattice. Each individual consists of a row of cells. The genome of the individual codes for a network of regulatory interactions, which determines the spatio-temporal dynamics of the proteins within each cell (see d). b The initial conditions for each new individual at the start of its development. There are a growth zone with high morphogen and a ‘head’ region without morphogen. The morphogen dynamics may vary. Either they are imposed, yielding persistent posterior morphogen (left) the morphogen is kept at a high level in the posterior-most cell while decaying in the other cells, or the morphogen can become regulated by the network, so that only the initial conditions are specified (right). c Divisions are regulated by a division protein; when its level passes a threshold, the cell can divide. Upon division, the level of the division protein in both daughter cells is halved, but not the level of the other proteins. d At the end of development, the expression of the segmentation gene is averaged over a number of time steps, and from this the segment boundaries are determined. e The mutational operators acting on the genome