Brainless Slime That Can Learn by Fusing [The Atlantic]

Dated Dec 21, 2016; last modified on Thu, 02 Sep 2021

Building Transit Networks

Can a cell learn? When a part of the plasmodium touches something attractive, e.g. food, it pulses more quickly and widens. If a part meets something repulsive, like light, it pulses more slowly and shrinks.

The article regards this as flowing in the best possible direction without conscious thought.

/r/TIL: See also: ants, bees and soap film.

Given a petri dish modeled on the Greater Tokyo Area, with bits of food at major urban centers, the slime mold created a network almost identical to Tokyo’s rail network. Similar results achieved for other regions.

But this doesn’t mean the slime mold is as good as engineers. If an organism exhibits an algorithm, does that make it smart? A computer program that performs the slime mold’s algorithm can hardly be regarded as AI. Why is this different?

/r/TIL: The network is nowhere near optimal. It ignores underground water, elevation differences, terrain types. Furthermore, the network IRL was designed incrementally. If we could rebuild it from scratch, we could do better.

/r/TIL: Slime mold can do one thing: spread greedily. Given all railroad stops, a greedy algorithm will get a good approximation.

Bridge Experiments

The slime had to crawl over a bridge laced with repellents to reach some food. With more repetitions, they got used to the repellents and moved faster. However, given a long timeout, the habituation wore off and they were back to being repulsed. Ergo, slime molds can learn.

Not convinced. An alternate explanation: unless there’s an active mechanism for taking in stuff, the slime, like any organism, tends to remain the same (homeostasis). Exposure to the repellant makes homeostasis less of a barrier.

When naïve molds (those that hadn’t enountered the repellents) merged with habituated ones, the merged molds crossed the bridge more quickly. Even after re-separation, the formerly naïve ones still showed signs of habituation. Ergo, molds can transfer what they’ve learned.

Did the author mean they can transfer the concentration of repellents in their cells? My homeostasis hypthesis might explain this too.