In the 7 December Nature Grimson et al. report that, like metazoans, the slime mold Dictyostelium discoideum has a β-catenin involved both in signaling and in forming adherens junctions (Nature 2000, 408:727-731). The junctions form after the unicellular amoebae are starved and aggregate into a fruiting body, with junctions present only between cells at a constriction near the top of the stalk tube. In mutants lacking the β-catenin, most of the fruiting bodies collapse, and there is an additional signaling defect: a cell-autonomous failure to induce certain aspects of prespore gene expression. The existence of the Dictyostelium protein and a related protein in the plant Arabidopsis thaliana suggest that evolution of β-catenin may have been a prerequisite for all multicellular development.