Imagine that you are blind, deaf, and without any memory whatsoever. No long-term or short-term memory; you can’t even remember the last step you took. You may have been in this room a million times, finding your way around a basic obstacle a million times, but still, now you have nothing. This is more or less the plight of slime mold tested in a recent experiment done by researchers at the University of Australia (with results published yesterday in the Proceedings of the National Academy of Sciences) — how, without memory or any global awareness of an environment, can this unicellular organism find anything, like, say, food to survive? The slime mold could, as a species, wait around to evolve into a brain-having complex organism, or evolution could take the sort of shortcut it loves and select for the slime mold something simpler: external memory.The experiment and its results sound very simple. Slime mold, aka Physarum polycephalum, is made up of just one cell, and is capable of secreting, well, slime. The slime isn’t part of the creature: it isn’t alive. As the slime mold travels, it leaves behind a trail of this stuff. What’s interesting is that the creeping slime mold will turn away when it encounters that slime trail. It won’t cross its own slime path. It makes a choice to turn away — when confronted with two paths blocked by slime trails, the mold takes either one an equalish number of times. But if only one path is blocked by slime, the mold will take the unslimed path.Researchers tested out this behavior in a simple navigational problem: the mold was set in a petri dish with food at the other side and a U-shaped trap in the middle. Some dishes were covered completely by the slime, rendering its navigational potential moot. The other dish was just normal. For the few slime molds that made their way to the food with their slime navigation ability restricted — two-thirds just didn’t — it took almost 10 times as long. With slime powers enabled, 96 percent of the molds made it to the food within the experimental time limit of 120 hours. (No kidding: mold is slow.)What happens is more bizarre than it might already sound. The mold actually maps its entire environment with slime, creating a tubule passage to its goal. In other experiments with slime mold and mazes, they’ve been found to create whole networks of slime tubules between food sources. “Although such problems appear more complex than the U-shaped trap used in the present study,” the PNAS paper explains, “the organism essentially first constructs a map of its environment before constructing a solution. In essence, maze solving and network construction are analogous to programming an autonomous robot with a symbolic map of its environment.”This is all pretty cool, but here’s the kicker: “Our study is unique in providing empirical evidence of a spatial memory system in a nonneuronal, reactive organism, lending strong support to the theory that feedback from chemicals deposited in the environment was the first step toward the evolution of memory in organisms with more sophisticated neurological capabilities than our slime mold.” In other words, memory on Earth was born in slime.Reach this writer at michaelb@motherboard.tv.
Advertisement
