Developmental biology: How the lizard gets its speckled scales.

Abstract

Can a reptile compute? In one species of lizard, Timon lepidus, the colour and pattern of its scales evolve in a manner akin to a discrete rule-based computation called a cellular automaton. See Letter p.173 Macroscopic patterns in the animal world, such as zebra stripes and leopard spots, can be described by dynamical processes at the level of biological cells acting within the reaction–diffusion framework. Liana Manukyan et al. discover a remarkable mechanism of pattern formation in ocellated lizards. They recorded the changes in skin patterning of several lizards over four years of development and find that their skin colour changes at the level of individual scales. The patterns appear to be produced by a hexagonal cellular automaton, in which the skin scales are the discrete units. Mathematical theory shows that such a discrete system can emerge from the continuous reaction–diffusion framework when taking into account variations in skin thickness. The intriguing conclusion is that cellular automata are not just abstract computational systems, but can directly correspond to processes generated by biological evolution.