Slime Mold MazeIn 2000 Toshiyuki Nakagaki announced that an amoeba-like slime mold was able to find the shortest distance through a maze, which is nearly the equivalent of saying a bit of Jello was able to jump up and run out of the refrigerator by itself. How did a nearly inanimate object solve such a complex problem?

(food is yellow and slime mold is white in the picture to the right)

First, what is a slime mold? From the introduction to Steven Johnson’s 2001 book, Emergence:

If you’re reading these words during the summer in a suburban or rural part of the world, chances are somewhere near you a slime mold is growing. Walk through a normally cool, damp section of a forest on a dry and sunny day, or sift through the bark mulch that lies on a garden floor, and you may find a grotesque substance coating a few inches of rotting wood. On first inspection, the reddish orange mass suggests that the neighbor’s dog has eaten something disagreeable, but if you observe the slime mold over several days — or, even better, capture it with time-lapse photography — you’ll discover that it moves, ever so slowly, across the soil. If the weather conditions grow wetter and cooler, you may return to the same spot and find the creature has disappeared altogether. Has it wandered off to some other part of the forest? Or somehow vanished into thin air, like a puddle of water evaporating?

Slime molds are really groups of tiny amoeba which are normally sliding around the forest floor individually. Occasionally they will coalesce into a larger blob. There is no central commander telling the individual cells when to come together or disperse. Like ants, they use pheromone trails. The individual cells release pheromones based on their assessment of the conditions. Using a type of chemical democracy, when the pheromone trail gets intense enough the slime mold cells pile together to form a larger being.

When you think of a slime mold like an ant colony it becomes clear how it solves the maze. Scout cells spread out, and pheromone trails eventually build up along the successful paths helping the individual cells find the most efficient route.

Here’s a close up time-lapse video of a slime mold moving.

1.5 minutes. Link to Video

Slime molds are so close to being both plant and animal that it’s like they can’t make up their minds. And they’re thinking now that maybe this is who’s been running the earth all this time.

David St. Hubbins, This is Spın̈al Tap