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Slime mold validates efficiency of Tokyo rail network


slime mold network train tokyoWhat do Tokyo commuter-rail designers and the slime mold Physarum polycephalum have in common? The two will build strikingly similar networks.

A Japan-based research team found that if they placed bits of food (oat flakes) around a central Physarum in the same location as 36 outlying cities around Tokyo, the mold created a network connecting the food sources that looked rather like the existing rail system. And when comparable "topographical barriers" were introduced onto the experimental plane, the links were even more similar.

Coincidence? Not at all, concluded the authors of the study, which was led by Atsushi Tero of the Research Institute for Electronic Science at Hokkaido University in Sapporo.

Like the humans behind a constructed network, the organism is interested in saving costs while maximizing utility. In fact, the researchers wrote that this slimy single-celled amoeboid can "find the shortest path through a maze or connect different arrays of food sources in an efficient manner with low total length yet short average minimum distances between pairs of food sources, with a high degree of fault tolerance to accidental disconnection"—and all without the benefit of "centralized control or explicit global information." In other words, it can build highly efficient connective networks without the help of a planning board.

Far from a one-off biological curiosity, this experiment led the researchers to develop a mathematical algorithm for their model of adaptive network construction, which can be applied to other microbiological problems—and macro technological ones.

"Self-organization, self-optimization and self-repair as it naturally occurs in the slime mold Physarum polycephalum are capabilities that may be required for technological systems such as mobile communication networks or networks of dynamically connected computational devices," Wolfgang Marwan of the Magdeburg Centre for Systems Biology at Otto von Guericke University in Magdeburg, Germany, wrote in a perspectives piece that accompanies the study, both of which will appear in the January 22 issue of Science.

Marwan called the mathematical model "beautifully useful." He added that: "It quantitatively mimics phenomena that can be neither captured nor quantified by verbal description alone." All aboard the slime mold express. 

Image of slime mold's network construction among food sources after 26 hours (yellow "Tokyo" is the mold center and white dots were food placed in the same position as nearby cities), which strongly resembles existing railway lines, courtesy of Science/AAAS

The views expressed are those of the author and are not necessarily those of Scientific American.

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