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If slime mould ruled the world


Slime mould grows on agar continents between oat flakes in Andrew Adamatzky's experiments on world colonisation.
Photograph: University of the West of England

Given enough agar and oats, how would the amoeba-like slime mould go about colonising the Earth?

Posted by Ian Sample
Friday 21 September 2012 10.51 EDT

One question never far from scientists' minds is how events might unfold were a giant slime mould to emerge in the Far East and embark on global domination.

History tells us what happened when restless humans set out into the world. Kingdoms rose and fell as wars raged. Urban centres grew and connected. Trade networks spread, first across countries, later spanning whole continents.

But slime mould is a different beast. Would the same scenarios play out as it colonised the world? After a series of simple experiments involving agar, a globe, a bag of oats, and an obliging slime mould, an answer, of sorts, is now at hand.

Andy Adamatzky [ http://uncomp.uwe.ac.uk/adamatzky/ ], director of the Unconventional Computing Centre [ http://uncomp.uwe.ac.uk/ ] at the University of the West of England in Bristol, picked slime mould – an amoeba-like, single-celled organism, Physarum polycephalum [ http://en.wikipedia.org/wiki/Physarum_polycephalum ] – as a harmless and friendly creature to work with. In its vegetative phase, it goes in search of food by extending "protoplasmic tubes", which transport nutrients and metabolites through the organism's body.

Left to their own devices, slime moulds establish protoplasmic networks that maximise the nutrients they can draw from nearby food sources. This ability makes them natural path-computing machines, says Adamatzky. In the arcane language of the field, he says the organism "acts like an amorphous massively parallel computer, with distributed inputs, or sensors, decentralised information processing and decision making and parallel actuation."

The impressive behaviour of P. polycephalum has been likened to a primitive form of intelligence. The Japanese scientist Toshiyuki Nakagaki at Hokkaido University has reported "smart behaviour [ http://www.ncbi.nlm.nih.gov/pubmed/11763236 (and see the post to which this is a reply)]" in a slime mould that solved a maze after morsels of food were placed at the start and finish points. The slime mould grew through the maze, stumbled upon the food and then withdrew its protoplasmic tubes from dead ends. Not bad for a creature with no brain.

Adamatzky took a different tack. "I poured hot agar gel on a globe to make several good layers, then cut out continents and removed agar corresponding to oceans, seas, and large lakes. Then I placed oat flakes in the locations of the most populated cities and inoculated slime mould in Beijing."

That's a globe of agar continents with oat flakes in place of major conurbations, and a starter colony of slime mould in the capital of China.

Science is not for the impatient. Covering a globe with agar takes time. You have to pour it on layer by layer and let it cool. Then you have to cut round the continents and peel off the seas.

And that's before you even get started. It takes over a week for slime mould to colonise a 15cm-diameter globe. "The real challenge was to be patient," says Adamatzky.

Typically, Physarum set out from Beijing and hooked up with oat flakes in Seoul and Tokyo, before colonising both Koreas and Japan in less than a day. From there it moved on to Hong Kong and Hanoi. A short branch would link up with Ho Chi Minh and Jakarta, and occasionally bridge over to New Zealand and Australia. The main branch pressed on, from Hanoi to Kolkata, Delhi, Tehran, Istanbul and London.

Most surprising to Adamatzky were the patterns that emerged over time. The slime mould recreated more than 76% of the Great Silk Road [ http://en.wikipedia.org/wiki/Silk_Road ] trading routes and parts of the Asian Highway Network [ http://en.wikipedia.org/wiki/Asian_Highway_Network ].

"It is not just [taking] the shortest path," said Adamatsky. "The slime mould's behaviour is affected by a combination of chemo-attractant gradients released by several metropolitan areas and shapes of continents."

Here's an early version of the paper [ http://arxiv.org/abs/1209.3958 ], due to be published in the International Journal of Bifurcation and Chaos [ http://www.worldscientific.com/worldscinet/ijbc ].

And what does all this tell us? Adamatzky thinks we have plenty to learn from these brainless organisms. He wants the work to inspire fresh thinking on how ancient roads came to be.

But that's not all. The creature's behaviour might spur unorthodox approaches to planning future traffic routes, or predicting the spread of global disease. In taking over the planet, slime mould might help us find our own way in the world.

© 2012 Guardian News and Media Limited

http://www.guardian.co.uk/science/blog/2012/sep/21/slime-mould-world [with comments]

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