Black

The scales of the ocellated lizard are surprisingly coordinated

ocellated lizard
SPECKLED SKIN The green and black spots on the back of an ocellated lizard are arranged according to the rules of a cellular automaton, a concept from computer science. Scales flip colors depending on the colors of their neighbors.

A lizard’s intricately patterned skin follows rules like those used by a simple type of computer program.

As the ocellated lizard (Timon lepidus) grows, it transforms from a drab, polka-dotted youngster to an emerald-flecked adult. Its scales first morph from white and brown to green and black. Then, as the animal ages, individual scales flip from black to green, or vice versa.

Biophysicist Michel Milinkovitch of the University of Geneva realized that the scales weren’t changing their colors by chance. “You have chains of green and chains of black, and they form this labyrinthine pattern that very clearly is not random,” he says. That intricate ornamentation, he and colleagues report April 13 in Nature, can be explained by a cellular automaton, a concept developed by mathematicians in the 1940s and ’50s to simulate diverse complex systems.

A cellular automaton is composed of a grid of colored pixels. Using a set of rules, each pixel has a chance of switching…