Alan Turing's 60-Year-Old Prediction About Patterns 
in Nature Proven True
Posted By: Virginia Hughes
Smithsonian Magazine
February 21, 2012
http://blogs.smithsonianmag.com/science/2012/02/alan-turing-predicted-natures-stripes-and-patterns/

Nature, for all of its free-wheeling weeds and lightning
strikes, is also full of biological regularity: the rows
of an alligator's teeth, the stripes on a zebrafish, the
spacing of a chicken's feathers. How do these patterns
arise?

Sixty years ago, with nothing but numbers, logic and
some basic biological know-how, mathematician Alan
Turing (best known for his pioneering work on artificial
intelligence) came up with an explanation. He proposed
that two chemicals-an "activator" and an "inhibitor"-
work together, something like a pencil and eraser. The
activator's expression would do something-say, make a
stripe-and the inhibitor would shut off the activator.
This repeats, and voilà, stripe after stripe after
stripe.

On Sunday, researchers reported the first experimental
evidence that Turing's theory is correct, by studying
the eight evenly spaced ridges that form on the roof of
a mouse's mouth. (People, by the way, have four such
ridges on each side, which help us feel and taste food.)

The scientists discovered that in mouse embryos, a
molecule called FGF, or fibroblast growth factor, acts
as a ridge activator, and SHH, or sonic hedgehog, acts
as an inhibitor. When the researchers turned off FGF,
the mice formed faint traces of the ridges that are
normally made. Conversely, when they turned off SHH, the
ridges morphed into one big mound. Changing the
expression of one of these partners influenced the
behavior of the other-just as Turing's equations
predicted.

Tragically, Turing would never know the importance of
his contributions to developmental biology. The British
government convicted him of homosexual acts in 1952 (for
which it recently apologized), and punished him with
chemical castration. Turing took his own life in 1954.
This June is the 100th anniversary of his birth.

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