Brainless, Footless Slime Molds Are Weirdly Intelligent and Mobile

We humans rely on our brains for cognition, but other animals have the ability to reason, learn, plan, solve complex problems, etc. without such a giant brain as ours. Take, for instance, the octopus — a cephalopod closely related to clams and snails. It has a brain, but most of its neurons are spread throughout its squishy body — mostly its arms. Still, an octopus has an undeniable intelligence: the kind that can tell the difference between humans that are dressed identically or can even make an escape from its tank, out a drainpipe and back into the ocean. But this impressive cognitive functioning bears no physiological relationship to ours — the neural processing equipment of an octopus evolved completely separately from ours, because our evolutionary lineages separated over 460 million years ago.

But slime molds don’t have brains or even anything that resembles a neuron. Still, though, scientists can press plasmodial slime molds into solving mazes. So, while the process of learning is completely different in each case, the outcome for a slime mold, an octopus and a human can look basically the same.

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One type of learning slime molds are capable of is habituation. You do this too — you can get used to the temperature of a cold lake after a few minutes, or the initially unpleasant buzzing sound of a fluorescent light in a room — your brain helps you ignore the annoying sensation of cold or noise. But the unicellular slime mold Physarum polycephalum can habituate to environments and chemicals they don’t love — acidic, dusty, dry, salty places or chemicals like caffeine or quinine — if it means they’re rewarded for putting up with it.

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Not only can slime molds habituate to less-than-ideal circumstances if it means they’ll be rewarded, they also seem to be capable of memory. Physarum polycephalum — the same, oft-studied species from the habituation study — seems to be able to remember things. An experiment involving slime molds that were intentionally habituated to salt, a known repellent, before going into a dormant period, showed that they remembered how to become habituated to living in a very salty environment after a year of lying dormant. They also seem to be able to decide which direction to travel based on the food they’ve encountered there before.

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Just wait — in a few years the slime mold will score a 1,200 on the SAT and scientists will really have some explaining to do.