Reaction–diffusion systems are a way to model the interaction between two chemical or biological substances. The substances react inside a virtual “petri dish”. The substrate substance grows by consuming the activator substance. The activator is replenished over time. Both substances also diffuse by spreading at a given rate.

This particular reaction–diffusion system is based on the Gray–Scott model. It is governed by a feed and a kill rate. Various combinations of these variables can cause intricate, organic patterns to emerge. In this animation the simulation’s “petri dish” is projected onto a sphere. The feed and kill rates are adjusted slightly over space and time.