“And the Rod Starts to Swing”. Morphogens, Instabilities and Imaginary Organisms in Turing’s Approach to Biology

A very rich bibliography exists today on Alan Turing's 1952 article, “The Chemical Basis of Morphogenesis” but many questions still remain for the reader: why does Turing, one of the fathers of computer science and of the notion of program, not use an informational metaphor associated with the notion of genetic program in his work on morphogenesis and prefer to embark on a modeling approach using a system of differential equations involving mathematics very far removed from his previous fields of work? Where does he draw his modelling inspiration, both from the point of view of the mathematics employed and from the point of view of references to biology?

In this essay we will address these questions by highlighting the morphological connotations of Turing's work in biology, that deeply renew D’Arcy Thompson’s morphology: the definition of morphogens, the establishment of instabilities as a condition for symmetry breaking, and the relations between numerical computation and analytical theory.