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Wednesday 4 April 2012

Engineering Slime

In the shadows, beneath decaying logs and leaves, shying away from the light lurks an unlikely civil engineer. The slime mould Physarum polycephalum (the “many headed slime”) is the most intelligent of scum. It can navigate a maze and anticipate a natural disaster – and now it can create a road network.

Unconventional computer scientists Andy Adamatzky and Jeff Jones of the University of West England have been using P. polycephalum as an unconventional computing tool to solve various problems, one of the most intriguing of which being the mapping of road networks across the world.

They did this by inoculating an area of agar gel representing the capital city of the country with the slime mould and using oat flakes as other major cities. Once inoculated, the Physarum will extend tendrils (the “roads”) in the direction of the oat flakes in search of nutrition, finding the shortest routes from the “capital” to the nearest oat flake city and between that and other cities. This creates the Physarum’s road map of the country.



From the videos above you can see the Physarum extending its gloopy tendrils across the land. This is called amoeboid movement, where the cell will move by extending its gooey self in the direction of a stimulus. And therein lies Physarum polycephalum’s smarts.

It collects information from its environment and makes an informed decision in its actions – just like you do (or should do at least). In detecting a “good” stimulus (i.e. the oat flakes) it will move towards it and in detecting a “bad” one (e.g. a poison) it will avoid it. This phenomenon is called chemotaxis and is displayed by almost all microbes to some extent. P. polycephalum will also respond to a lack of stimulus by retracting tendrils which are proving to be fruitless in their search.

The researchers also used bad stimuli (chemorepellents) to mimic a disaster which would make a route non-traversable. Adamatzky and Jones’s disaster was a grain of salt placed in a simulated urban area. This caused diffusion of sodium chloride throughout the medium which repels the Physarum. The slime mould responds by reconfiguring its road network to avoid the salt disaster.

As shown, the slime mould makes a road network which matches the one already present in the UK and in the USA. Adamatzky and Jones speculate that our road networks are similar to the slime mould’s as ours were initially forged by migrating animals.


Japanese scientists led by Prof. Atsushi Tero of Hokkaido University have also used similar experiments using Physarum polycephalum to create a rail network to compare the efficiency of the slime mould to that of Japanese civil engineers – using the Tokyo rail network as their model, naturally. They concluded that Physarum polycephalum is at least "comparably efficient" in this role.


This draws an interesting parallel with what we see as the uniquely human concept of engineering things to our own ends. How human is it really when the many headed slime can do it just as well?