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Some Natural Networks Replicate Human Design

Posted By Prucia Buscell, Thursday, January 28, 2010
Updated: Thursday, February 17, 2011
What living organism can solve complex network engineering problems despite having no brain?

Slime molds are unusual-they're neither plant, nor animal nor fungus, but they can create a community of cells that follows simple rules to travel, solve problems, and adapt to environmental conditions. Scientists from England and Japan tested the slime mold's capacities by putting 36 oat flakes in a pattern that represented the position of cities around Tokyo. Oat flakes are a slime mold treat. After a day, the mold had built a network of nutrient-carrying tubes that looked pretty much like the Tokyo rail system, which carries millions of people every day among far-flung locations. It's a model of efficiency, designed by talented engineers and experts in mass transit.

Research by Toshiyuki Nakagaki of Hokkaido University and Mark Fricker of the University of Oxford is reported in the January 22 issue of Science. A story in Wired, by Laura Sanders, reports that initially, the mold dispersed evenly, creating a mesh around the flakes. But within hours, it refined its design,strengthening some nutrient tubes and connections to sustain iteslf, while other tubes disappeared. The researchers used the behavior of the mold to create a mathematical description of the network formation. Fricker explains in the Wired story that such a malleable system could be useful to create networks that change over time, such as wireless fire and flood warnings. In addition, decentralized, adaptable networks would be useful for soldiers in battle, for swarms of robots exploring hazardous places, and they could help scientists understand how blood vessels grow to support tumors.

"A Life of Slime," a story in the Economist, explains that the species used in the experiment, physarum polycephalum, a plasmodium slime mold, is membrane-bound bag of protoplasm that forms when single cells mass together and fuse into a huge cell with multiple nuclei. Cellular slime molds, another variety, spend most of their lives as separate single-celled organisms, but upon released of a chemical signal, they aggregate into a swarm. P. polycephalum often travels across damp forest floors, and as it forages for food, it puts out protrusions of protoplasm, creates nodes and branches, and its body forms a network of tubes that carry nutrients. Both stories note that the networks not only find the shortest distance between different points. They feature redundant connections that allow for resilience in case of breakage-just like well-designed networks created by human engineers. No one know how these brainless organisms self-organize organize with such amazing success. The Economist story notes that in a similar experiment, the slime mold created a network that was quite similar to highways that connect England's principal cities.

You can watch a slime mold network forming on YouTube, and listen to Professor Nakagaki's lecture on organization in an amoeboid system.

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