The scale of what the world lost when Alan Turing was hounded to suicide has become even clearer, with the vindication of his only paper on biology, sixty years after it was written.
Saving Britain during its darkest hour and laying the basis for computers just wasn't enough for Turing; he also was the first to propose a chemical theory of morphogenesis, the process by which an organism gains its shape. His paper, The Chemical Basis for Morphogenesis was published in 1952 in the Philosophical Transactions of the Royal Society B, shortly after Turing was sentenced to chemical castration for homosexuality.
Turing wrote, “It is suggested that a system of chemical substances, called morphogens, reacting together and diffusing through a tissue, is adequate to account for the main phenomena of morphogenesis. Such a system, although it may originally be quite homogeneous, may later develop a pattern or structure due to an instability of the homogeneous equilibrium, which is triggered off by random disturbances.”
The paper sought to answer the question of how an embryo made up of identical cells can transform into something with specialist parts and a specific shape. Turing's idea rested on the existence of excitatory agents that cause reactions to happen and inhibitory agents to suppress them. This allows patterns of chemically different cells to form in the embryo of complex organisms, including ourselves.
A “mathematically convenient, though biologically unusual” example of a ring of cells was modelled, and Turing found that six shapes were possible, the most interesting of which were those with stationary waves he suggested might explain biological phenomena such as whorled leaves. He matched other patterns to different forms observed in nature.
The excitatory/inhibitory model is now well established, but despite the enormous progress in biochemistry since the 1950s experimental evidence of the theory as a whole has only appeared now, in a paper in the Proceedings of the National Academy of Sciences.
Professors Seth Fraden and Irv Epstein of Brandeis University created rings of synthetic, cell-like structures using reactant pairs. By operating in an abiological system they removed the possibility of distortions from other factors and produced all six of the patterns Turing predicted. As he anticipated, the differentiated structures also change size in response to osmosis.
The experimental findings go beyond Turing's model, producing a seventh pattern Fraden and Epstein explain with an extension of Turing's work. They propose that the findings may be useful for growing, rather than building, soft robots, which would then be powered computer codes developed from Turing's more famous activity.
It took until 2009 for the British Government to apologise for its persecution of Turing, and Christmas Eve 2013 for an official pardon to be issued.
