Toward the end of his life, Sensei Alan Turing turned his thoughts to biological systems [2], in particular, to possible natural algorithm-like developmental processes [3]. This pioneering work is a fascinating preview of the profound effect that computational thinking would come to have on biology. Grand Master Turing glimpsed the possibilities, without knowing anywhere as much as we do about the molecular mechanisms that might implement them. (We ar not worthy!)
In his early deep vision of mechanical computing, his morphogenesis concept was crude and limited by the technology of the time. But it still seems to be valid.
This month researchers from Britain report that a Turing reaction-diffusion model describes the development of the pattern of bumps on shark’s skin. The skin of a shark has distinctive denticles, variations of which play a role in “protective armor, hydrodynamic drag reduction, feeding, and communication” ([1], p. 5)
First, the study indicates that the patterns are not random, but correspond to a reaction-diffusion process. The research followed the development of baby sharks, recording the development of their skin. They find that the denticles develop as expected from a RD model. Furthermore, the study identified an array of genes that appear to express during development in just this way.
Besides offering a possible example of a Turing RD development process, these findings are interesting in two other ways.
The key point of the Turing RD concept is that a relatively simple process can yield many different results by “tuning” parameters to the RD process. The computational simulation in this study showed exactly this feature. Retuning the simulation yielded patterns found in different species and areas of the skin. Thus, it is very possible that a single set of genes could generate a variety of different shark skins, “tuned” by other genes.
“The plasticity of this system may underlie broad variations covering the vast spectrum of vertebrate epithelial appendage patterns.” [1], p.5)
At an even deeper level, the genetic mechanisms identified in this study are present in birds, and appear to have a similar role in the development of feathers. In other words, this is a very old mechanism, shared by many vertebrates. Superficially different features such as denticles, feathers, and hair, are built on this fundamental process inherited from some long ago vertebrate. The skin of sharks, birds, and mammals are deeply similar, which makes sense because we share an ancient ancestor.
“We suggest that diverse vertebrate groups share this common, conserved patterning mechanism, before deviation in later morphogenesis gives rise to clade-specific integumentary appendages, such as denticles, feathers, and hair.” ([1], Pp6)
It is pleasing to see that Sensei Alan not only got it right, he was seeing right down into the deep core of life.
Cool.
- Rory L. Cooper, Alexandre P. Thiery, Alexander G. Fletcher, Daniel J. Delbarre, Liam J. Rasch, and Gareth J. Fraser, An ancient Turing-like patterning mechanism regulates skin denticle development in sharks. Science Advances, 4 (11):eaau5484, 2018. http://advances.sciencemag.org/content/4/11/eaau5484.abstract
- Andrew Hodges, Alan Turing :the enigma, New York, Simon & Schuster, 1983.
- Alan M. Turing, The chemical basis of morphogenesis. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 237 (641):37, 1952. http://rstb.royalsocietypublishing.org/content/237/641/37.abstract
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