Slime mold – our memory ancestor

The humble slime mold … more to it than first appears

Slime mold

The splendidly named dog vomit slime mold might not look very inspiring, but it might actually be responsible for the origin of memory.

If you came across a slime mold fungus on your travels, which would likely be under an undisturbed log or some decaying leaves, you could be forgiven for not giving it a second thought. If you had an abiding interest in natural history, and mold and fungi in particlular, you might ask yourself is slime mold a fungus or not, something which has often been debated, but that’s probably as far as it would go. You wouldn’t feel any impulse to greet it as a long lost relative, or congratulate it on its amazing development, mainly because, although it looks like some sort of rudimentary animal it’s actually a single massive cell formed when millions of microscopic Physarum come together in search of food.

But the truth is, we owe quite a debt to slime mold, apparently. While we pride ourselves on our ability to remember things in a clever, structured way, it may have all begun with the early memory work of the humble slime mold.

Research on slime mold fungus

It may seem like a lot to credit slime mold with, but Audrey Dussutour, a collective behavior specialist at France’s National Center for Scientific Research, believes that even though technically not an animal, and literally being unicellular, slime molds do in fact remember where they’ve been. Incidentally, the slime mold study was published in October 2012 in Proceedings of the National Academy of Sciences. “It doesn’t have a brain,” Dussutour says. “It doesn’t even have a neuron. It has to do everything with just one cell”. And it seems to do it incredibly well.

The reasoning behind it is this: slime molds move around, very slowly, foraging for food, and the last thing they want to do is waste valuable time and energy going over old ground. Researchers thought that maybe their slime trails left a kind of message, so they experimented. They watched the slime trails carefully and noticed that the slime molds repeatedly avoided them, so the hypothesis seemed to be true – they would do anything they could to avoid crossing their earlier paths.

Slime trails as a rudimentary memory

They then put the slime molds into petri dish mazes with food sources hidden in U-shaped traps. It was the kind of test used to measure the ‘intelligence’ of autonomous robots and can’t be solved easily without the ability to remember where you’ve already been. As long as the trails were left undisturbed, the slime molds did remarkably well on the test. The trails and the ability to sense them served as a memory of sorts, albeit an external one, since the slime molds don’t have a brain to store it in.

Hansel and Gretl

Hansel and Gretel used a very simple but effective method to retrace their steps. Slime mold is just as smart!

Not impressed? Okay, imagine going somewhere quite distant without any means of navigating … no map, no compass, no mobile phone, no satnav, nothing. Oh, and no eyes to see with! Then imagine trying to find your way back. Not so simple, huh? Perhaps the only way you could manage it would be to leave a trail of pebbles or breadcrumbs, like in Hansel and Gretel. But this is slime mold we’re talking about. It can’t collect pebbles and scatter them along its path, but it can manage the same trick by leaving its own slime trail. Pretty neat trick too, I’d say!

“It’s very simple, but it works exactly like a memory of a place you’ve been,” said Dussutour. “It’s very difficult for robots to solve what the slime molds did”. She likened it to another of her research interests: pheromone trail-sensing used by ant colonies. “If you had a competition between slime molds and ants, the slime molds would win,” she said. High praise indeed, since ants are some of the most advanced social animals on the planet, for their size.

Slime mold fungus predates plants and animals

Physarum are thought to be some of the earliest forms of life, predating both plants and animals, and although these fungi literally have just one cell they group together in vast numbers to achieve their goals. They manage to ‘remember’ where they’ve been, even without a brain, and this could be the first step on the road to cerebral development.

So next time you’re congratulating yourself on your memory achievements (and you should!), spare a thought for the humble slime mold, who may well have been responsible for the memory capabilities we all have today.

Or even our very brains!


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