In D. discoideum, the proportion of prespore and prestalk cells in slugs are regulated to the approximate proportions of stalk and spores in the fruiting body. However, in other species such as P. violaceum, P. pallidum and D. lacteum, cells first differentiate into prespore cells only to dedifferentiate into stalk cells at the tip. (58, 59) Apart from stalk cells and spores, D. discoideum has three more cell types, the basal disc, upper cup cells and lower cup cells, that each display specific patterns of gene expression. When and how did cell-type proportioning and greater cell-type specialization evolve?