Orientation maps from pattern formation

Alan Turing first proposed in 1952 that simple interacting chemicals, which he called morphogens, can create complex patterns that bear resemblance to ones found in biology. For example, he postulated one type of morphogen could result in the darkening of hair (called an activator), whereas another type could bleach it (called an inhibitor); as these morphogens diffuse across the animal's coat, typically at different rates, their reactions with each other can create intricate pigmentation patterns. The reaction–diffusion equations that he developed have been used to replicate the spots on a leopard's coat, the stripes on a zebra's hide, and can even account for how these patterns change as an animal ages.