The origin of biological pattern and form is still largely a mystery. How do identical cells differentiate into a complex organism? Even limiting ourselves to examining only the skin coloring of animals, how is it that each animal develops a unique pattern?
Alan Turing suggested an answer to these questions in 1952 in a paper entitled the Chemical Basis of Morphogenesis. His idea, called Reaction-Diffusion, is an explanation of how our cells, starting from uniform, identical units can differentiate into complex structures. Reaction-diffusion is a chemical signalling process where a simple system of chemicals is diffusing and interacting with one another. In the right circumstances, these systems can form large scale patterns while locally each cell acts identically. Reaction-diffusion has been used to model the intricate patterns found on the skin of many types of animals, from the spots of leopards to the radiating stripes of angelfish. Additionally, it has been proposed as a mechanism for the formation of many biological structures such as limbs and organs.