From Aggregate to Organism: Emergence of Multicellularity in Sea Sponges

What marks the transition from a loosely connected collection of cells to a cohesive multicellular organism that behaves as an individual? We address this fundamental question using sea sponges as a model system. Remarkably, when sponge tissue is dissociated into single cells, these cells can migrate, reaggregate, and re-differentiate to form a fully functional sponge, a striking example of self-organization. We combine experiments and theory to quantify the dynamics of cell aggregation and the mechanical communication that emerges between cells. From these measurements, we identify the minimal set of interactions required to establish multicellularity. Implementing these interaction rules in silico, we reconstruct the emergence of multicellular organization from initially independent cells. Our findings illuminate how multicellularity can arise as a biophysical consequence of collective dynamics and self-organization, providing new insights into one of life's most profound transitions.