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

Abstract

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.