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In the early 1950s, Alan Turing showed his colleagues a drawing with
irregular black-and-white patches, asking them whether they agreed that
it looked like a cow. In 1952 he published 'the chemical basis of morphogenesis',
in which he proposed a mechanism for the creation of animal markings. A chemical
called a morphogen was produced by local reactions and diffused across the embryo,
laying down a pre-pattern. At a late stage of development, this formed the basis of
a pattern of pigments. Although these reaction-diffusion equations do not correspond
in detail to many features of the biology, the patterns that they naturally form are
remarkably similar to those found on many animals, including irregular and convoluted
stripes on fish and some intricate patterns on seashells. The talk will be an informal
illustrated discussion of these Turing patterns, from the point of view of modern
theories of pattern formation.
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