Lizards and snakes — collectively known as squamates — often sport intriguing macroscopic skin patterns, resulting from the different colours exhibited by individual, microscopic skin cells. Changes in a squamate's skin pattern are due to interactions between skin cells, and are traditionally described in terms of reaction–diffusion systems involving nonlinear partial differential equations.
But now, Liana Manukyan and colleagues have found that as the ocellated lizard (Timon lepidus; pictured) ages, its skin pattern behaves as a cellular automaton. The reptile's mesoscopic scales form a quasi-hexagonal lattice of cells that are either green or black, and a nearest-neighbour rule defines how the instantaneous pattern follows from the configuration at the previous time step.
Manukyan et al. arrived at this conclusion by scanning the skin pattern of three lizards from about two weeks after hatching until they were three years old. From simulations and a mathematical analysis of the observed evolution of the reconstructed colour maps, the authors demonstrated that the changes were indeed compatible with a probabilistic cellular automaton. They were also able to show how the discrete automaton emerges from the continuum reaction–diffusion model.