Experimental observation of self-replicating spots in a reaction-diffusion system

IN his classic 1952 paper, Turing¹ suggested a possible connection between patterns in biological systems and patterns that could form spontaneously in chemical reaction-diffusion systems. Turing's analysis stimulated considerable theoretical research on mathematical models of pattern formation, but Turing-type patterns were not observed in controlled laboratory experiments until 1990^{2, 3}. Subsequently there has been a renewed interest in chemical pattern formation and in the relationship of chemical patterns to the remarkably similar patterns observed in diverse physical and biological systems⁴. Numerical simulations of a simple model chemical system have recently revealed spot patterns that undergo a continuous process of 'birth' through replication and 'death' through overcrowding⁵. Here we report the observation of a similar phenomenon in laboratory experiments on the ferrocyanide-iodate-sulphite reaction. Repeated growth and replication can be observed for a wide range of experimental parameters, and can be reproduced by a simple two-species model, suggesting that replicating spots may occur in many reaction-diffusion systems.