Alan Turing and “The Chemical Basis of Morphogenesis”

A. M. Turing (1912–1954) was one of the foremost thinkers of the 20th century. He contributed at least three original ideas in his life, a claim that not many can make. They were the ‘Turing machine’, the ‘Turing test’ and the ‘Turing instability’. The aim of this article is to make some comments on the last of these. It forms part of the only biological work by him published in his lifetime, entitled “The Chemical Basis of Morphogenesis” [24], My comments begin as questions pertaining to its background, immediate reception and subsequent impact from the viewpoint of biology. No attempt is made to discuss the mathematical aspects of Turing’s analysis, interesting as they are because to do so would be redundant for the readers of this volume. This being Turing’s sole publication dealing with a conventional biological problem (i.e., ignoring for the moment what he had to say on the question of Mind), I will use “Turing’s paper” and “Turing’s contribution to biology” as if the two terms were interchangeable. Strictly speaking, this is not correct. Ward-law [26] finished and wrote up on his own the ideas about phyllotaxis that he had been discussing with Turing. There is also a volume of Turing’s Collected Works that includes later, incomplete developments on morphogenesis which appeared after his death [20]. More pertinently, neither contains essential information bearing on our assessment of The Chemical Basis of Morphogenesis — which, after all, is the only thing that Turing did that many biologists know, or know about.