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Weird Circles Keep Popping Up Around the World. Alan Turing Predicted Them in 1952.

Caroline Delbert
·3 min read

From Popular Mechanics

A pattern described by computer science icon and polymath Alan Turing continues to show up in new scientific research 70 years later. The “Turing pattern” is a widespread phenomenon where noisy systems form stable patterns after being stimulated. The latest example is in “symmetrically spaced” patches of desert grasses, which grow in naturally orderly equilibrium to maximize each patch’s access to limited water.

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In Africa and Australia, desert grasses grow in what are called fairy circles. In the new study, published in the Journal of Ecology, scientists explain:

“This pattern has been explained with scale-dependent ecohydrological feedbacks and the reaction-diffusion, or Turing mechanism, used in process-based models that are rooted in physics and pattern-formation theory.”

But modeling a true Turing pattern isn’t as simple as pointing and labeling. Scientists must analyze, which is more challenging in ecological examples where variables are greater. In this case, studying grasses up close turned up more interesting conclusions as well: healthier grasses had even tighter fairy circle patterns, indicating more adherence to the Turing pattern.

In addition, the scientists say they confirmed a long-held belief that these desert grass fairy circles act both for their own self protection and as a kind of irrigation system for the surrounding, even drier vegetation. Think about moisture-trapping particles mixed into commercial potting soil, iconic circular farm irrigation, or even carefully spaced yard sprinklers.

But the most literal analogy is the little hollow spike sold as a slow plant waterer. “The grasses act as ‘ecosystem engineers’ that modify their hostile, abiotic environment, leading to vegetation self-organization,” the researchers explain. Having a steady drip of gathered moisture means the area between these grasses can change their makeup and even support more robust ecological stacks including probiotic bacteria.

Photo credit: Stephan Getzin, et. al./Journal of Ecology
Photo credit: Stephan Getzin, et. al./Journal of Ecology
Photo credit: Public domain
Photo credit: Public domain

It’s a cool finding, but what does Turing have to do with it? Well, in 1952, he published a paper describing these mechanisms, also called Turing dynamics, Turing instabilities, and more. “This Turing mechanism is also known as reaction-diffusion mechanism or activator-inhibitor principle, and a key to forming spatially periodic Turing patterns is the presence of positive and negative feedback interaction at different spatial scales,” the scientists say.

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A “short-distance positive feedback and a long-distance negative feedback” combine to gather primary resources in the positive location and leave empty space in the further-away negative zone. The researchers explain:

“Here, the a priori assumption is that the roots of the Triodia plants induce an infiltration contrast and thereby trigger the positive short-range feedback loop where more vital and larger plants gain more water and thus have a disproportionally greater benefit than weaker neighbouring plants.”

This means the strong plants survive and thrive partly because they’re already in an area with concentrated resources.

Turing, who ScienceAlert points out was unlikely to ever be able to travel to Namibia, continues to create patterns of his own in research around the world.

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