If you think the liquid android in Terminator 2-the one that reassembled itself after being smashed into tiny droplets-is centuries off, think again. Robots built from small, intelligent, interchangeable modules are already squirming their way off the drawing boards in labs around the world, including Mark Yim's Modular Robotics Laboratory at the Palo Alto Research Center. A senior researcher at PARC, Yim has developed a bestiary of versatile "PolyBots," proving for the first time that different groupings of identical modules can locomote like a snake, a spider, a lizard, a wheel, and more. To Yim, these itinerant prototypes are early steps toward Proteus-like machines that adapt to new environments-say, the surface of a remote planet-by altering not simply their behavior but their very anatomy.

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