[Lapg] Railways and slime moulds /Network-engineering problems can be solved by surprisingly simple creatures

[Wesley Roe and Santa Barbara Permaculture Network]

Railways and slime moulds
A life of slime
Network-engineering problems can be solved by surprisingly simple creatures
Jan 21st 2010 | From The Economist print edition
SPL
http://www.economist.com/sciencetechnology/displaystory.cfm?story_id=15328524




Show me the way to Shinjuku
FROM adhesives that mimic the feet of geckos to swimsuits modelled on 
shark skin, biologically inspired design has taken off in recent 
times. Copying nature's ideas allows people to harness the power of 
evolution to come up with clever products. Now a group of researchers 
has taken this idea a step further by using an entire living 
organism-a slime mould-to solve a complex problem. In this case, the 
challenge was to design an efficient rail network for the city of 
Tokyo and its outlying towns.

Slime moulds are unusual critters-neither animal, nor plant nor 
fungus. If they resemble anything, it is a colonial amoeba. Physarum 
polycephalum, the species in question, consists of a membrane-bound 
bag of protoplasm and, unusually, multiple nuclei. It can be found 
migrating across the floor of dark, damp, northern-temperate 
woodlands in search of food such as bacteria. It can grow into 
networks with a diameter of 25cm.

When P. polycephalum is foraging, it puts out protrusions of 
protoplasm, creates nodes and branches, and grows in the form of an 
interconnected network of tubes. As it explores the forest floor, it 
must constantly trade off the cost, efficiency and resilience of its 
expanding network.

Since the purpose of this activity is to link food sources together 
and to transport nutrients around the creature, Atsushi Tero at 
Hokkaido University in Japan and his colleagues wondered if 
slime-mould transport networks bore any resemblance to human ones. As 
they report in Science, they built a template with 36 oat flakes (a 
favoured food source) placed to represent the locations of cities in 
the region around Tokyo. They put P. polycephalum on Tokyo itself, 
and watched it go.

They found that many of the links the slime mould made bore a 
striking resemblance to Tokyo's existing rail network. For P. 
polycephalum had not simply created the shortest possible network 
that could connect all the cities, but had also included redundant 
connections that allow the creature (and the real rail network) to 
have resilience to the accidental breakage of any part of it. P. 
polycephalum's network, in other words, had similar costs, 
efficiencies and resiliencies to the human version.

How the creature does this is unknown, but Mark Fricker of Oxford 
University, who is one of Dr Tero's colleagues, speculates that the 
forces generated by protoplasm pulsating back-and-forth through the 
multinuclear cell are interpreted and used to determine which routes 
to reinforce, and which connections to trim.

Tokyo's is not the first transport network to be modelled in this 
way. A study published in December by Andrew Adamatzky and Jeff Jones 
of the University of the West of England used oat flakes to represent 
Britain's principal cities. Slime moulds modelled the motorway 
network of the island quite accurately, with the exception of the 
M6/M74 into Scotland (the creatures chose to go through Newcastle 
rather than past Carlisle).

Of course, neither Dr Tero nor Dr Adamatzky is suggesting that rail 
and road networks should be designed by slime moulds. What they are 
proposing is that good and complex solutions can emerge from simple 
rules, and that this principle might be applied elsewhere. The next 
thing is to discover and use these rules to enable other networks to 
self-organise in an "intelligent" fashion without human 
intervention-for example, to link up a swarm of robots exploring a 
dangerous environment, so that they can talk to each other and relay 
information back to base. The denizens of Carlisle, meanwhile, may 
wonder what objection slime moulds have towards their fine city.
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