(a) Multicellularity () rapidly evolves in a population of cells with . (b) Multicellularity only evolves when seasons are sufficiently long ; unicellular strategies evolve when seasons are short , and both strategies are viable depending on initial conditions for intermediate values of . The dashed line indicates the separatrix between the basins of attraction of the two evolutionary steady states; it is estimated as the mid-point where evolutionary simulations with consecutive initial values of evolve to alternative steady states. In both panes, is estimated as , where and are calculated from the and extracted from the system at evolutionary steady state. The initial J values, indicated by the dotted lines, are such that . (c) Snapshots of the spatial distribution of the population at evolutionary steady state for and MCS.