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Slime mold validates efficiency of Tokyo rail network

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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





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  1. 1. jtdwyer 3:53 am 01/22/2010

    The article states:
    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."

    I’m just guessing here, but I bet the slime mold has chemical receptors that preferentially directs growth to the nearest food source.

    I suspect my verbal summary better reflects the actual process producing the observed phenomena than the mathematical model which reportedly mimics its results. The model may be quite useful, but may not produce equivalent results in all circumstances. Mathematics is not always more precise than language.

    Link to this
  2. 2. Wayne Williamson 4:25 pm 01/22/2010

    jtdwyer…my guess is your correct.
    This can be applied to almost any living thing…find the shortest route and build upon it.

    Link to this
  3. 3. Quinn the Eskimo 3:04 am 01/23/2010

    So, we *can* talk our way out of next Tuesday Math Exam?

    I’m jus’ sayin’

    Link to this
  4. 4. jtdwyer 8:38 am 01/23/2010

    Quinn… – You could just skip it…

    Mathematics is extremely useful, but knowledge of mathematics is no substitute for understanding the problem.

    Link to this
  5. 5. focalist 5:41 pm 01/27/2010

    I think what’s most interesting is the concept of using biological models to examine non-biological systems. They seem to be leading into (but not quite saying) that at least for a simple purpose like this, a self-organizing goal-seeking network is something that nature creates herself.. and maybe we can look at HOW good ole mother nature does this, we can learn new ways to look at problems that are completely unrelated to slime molds, railways, or cell phone towers….

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  6. 6. salustri 2:16 pm 10/2/2010

    Math is "just" a language. While it can affect thinking processes, it is fundamentally just a way to express thought.
    The important human insight was the specifics of the analogy between the mold/food combo and the rail system.
    And the most important result is that no fancy shmancy AI program was needed to do this – just a plain old slime mold. This underscores that "instinct" rooted in just following basic laws of nature can beat out rational thinking. This isn’t a diss on rational thinking; it’s rational thinking that led us to this conclusion. Rather, it’s an observation that we shouldn’t be reinventing the wheel with weird, artificial theoretical models without first looking at what nature can do.
    I suspect that if we could understand exactly why the slime mold works this problem so well, we’d develop all kinds of new ways to solve all kinds of other problems.

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