Biology
Dictyostelium discoideum normally lives as solitary amoebae. Under starvation, they aggregate into a multicellular slug using cyclic AMP (cAMP) as a chemical signal.
Mechanism: starving cells emit cAMP pulses. Neighbors detect it, emit their own cAMP, and move up the gradient (chemotaxis). This creates spiral cAMP waves visible under microscope.
Keller-Segel model describes this mathematically — and predicts a blowup singularity (infinite density) in 2D, corresponding to perfect aggregation.
Click canvas to place cAMP sources. This models the aggregation center.