Soldier crabs, mictyris platychelus, Newman's Beach, Tasman Peninsula, Tasmania, Australia.
If you’ve heard of the game Minecraft, you may also have heard about all the folks who’ve built working virtual arithmetic logic units (ALUs) out of the LEGO-like game world itself. Sure, they’re more spectacle than useful, but incredibly cool to watch. So is it really that much of a stretch to find that someone’s taken crabs — actual, live, real-world crabs — and coaxed them into performing computer functions?
Computer scientists at the Kobe University in Japan did just that by placing soldier crabs in specially tailored environments to perform logic operations comparable to the elemental workings of a computer. Following up on a decades-old notion involving computing with billiard balls (more on that in a moment), the scientists showed both in computer models and lab experiments that “swarms of soldier crabs can implement logical gates when placed in a geometrically constrained environment.” Who knew?
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In a paper titled “Robust Soldier Crab Ball Gate” (noticed via Wired), the scientists write that “all natural processes can be interpreted in terms of computations.” And here’s where we start talking pool, as in the game played with billiard balls. A pair of computer scientists in the early 1980s proposed making a computer out of billiard balls. How? Instead of using electricity to convey signals to different parts of the computer, you’d pipe in billiard balls, whose collisions would dictate the output. If the balls collide with certain “gates” and bounce off, the output is based on the physics of the collision — or if they don’t collide, the lack thereof.
So crabs…because they’re just billiard balls with claws, right? Actually yes, for all intents and purposes here. Soldier crabs in particular exhibit unique flocking behavior: When two groups collide, they actually merge and continue moving in a direction related to the sum of their velocities, not unlike the way billiard balls behave when they smack into one another.
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To build their billiard/crab computer, the Kobe scientists took groups of 40 soldier crabs and placed them along channels that functioned as logic gates, in this case a Boolean OR and AND gate. To motivate the crabs, the scientists simulated a bird’s shadow (birds prey on soldiers crabs, thus the swarm’s inclination to scrabble). The relatively dependable OR gate was formed when swarms of crabs collided and merged into one, while the trickier AND gate, which worked less frequently, required the crabs to traverse one of three channels. The scientists note that “no crab was ever endangered” and that “the crabs were kept in comfortable conditions and after all experiments were released to their natural habitat.”
Sure, the practical uses for this sort of “biological computer” are pretty much zero, but then that’s what they said about Silly Putty back in the 1940s, too.
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