The chemical basis of morphogenesis. Offprint from: Philosophical Transactions of the Royal Society of London, Series B, Vol. 237, No. 641, 14 August, 1952. Turing’s last major published work, which was “in every respect ahead of its time” (Copeland, p. 510). Taking his cue from the zoologist D’Arcy Thompson, who held that the forms of living things are to be explained in terms of the operation of physical forces and mathematical laws, Turing presents here the first mathematical theory of embryology. “At a time when Crick and Watson were using X-ray diffraction to establish the structure of DNA, Turing was grappling with a theoretical understanding of how information might be spread and diffused at a chemical level. In a classic statement of the scientific method Turing wrote: ‘a mathematical model of the growing embryo will be described. This model will be a simplification and an idealisation, and consequently a falsification. It is to be hoped that the features retained for discussion are those of greatest importance in the present state of knowledge’. The result was applied mathematics par excellence. Just as the simple idea of the Turing machine had sent him into fields beyond the boundaries of Cambridge mathematics, so now this simple idea in physical chemistry took him into a region of new mathematical problems” (Hodges, p. 434). “Alan Turing’s paper, ‘The chemical basis of morphogenesis,’ has been hugely influential in a number of areas. In this paper, Turing proposed that biological pattern formation arises in response to a chemical pre-pattern which, in turn, is set up by a process now known as diffusion-driven instability.