Finally, the scientists let the slime molds rest for two days in situations where they were exposed to neither quinine nor caffeine, and then tested them with the noxious bridges again. “We saw that they recover—as they show avoidance again,” Dussutour said. The slime molds had gone back to their original behavior.

Of course, organisms can adapt to environmental changes in ways that don’t necessarily imply learning. But Dussutour’s work suggests that the slime molds can sometimes pick up these behaviors through a form of communication, not just through experience. In a follow-up study, her team showed that “naïve,” non-habituated slime molds can directly acquire a learned behavior from habituated ones via cell fusion.

Unlike complex multicellular organisms, slime molds can be cut into many pieces; once they’re put back together, they fuse and make a single giant slime mold, with veinlike tubes filled with fast-flowing cytoplasm forming between pieces as they connect. Dussutour cut her slime molds into more than 4,000 pieces and trained half of them with salt—another substance that the organisms dislike, though not as strongly as quinine and caffeine. The team fused the assorted pieces in various combinations, mixing slime molds habituated to salt with non-habituated ones. They then tested the new entities.

“We showed that when there was one habituated slime mold in the entity that we were forming, the entity was showing habituation,” she said. “So one slime mold would transfer this habituated response to the other.” The researchers then separated the different molds again after three hours—the time it took for all the veins of cytoplasm to form properly—and both parts still showed habituation. The organism had learned.

Hints of Primitive Cognition

But Dussutour wanted to push further and see whether that habituating memory could be recalled in the long term. So she and her team put the blobs to sleep for a year by drying them up in a controlled manner. In March, they woke up the blobs—which found themselves surrounded by salt. The non-habituated slime molds died, perhaps from osmotic shock because they could not cope with how rapidly moisture leaked out of their cells. “We lost a lot of slime molds like that,” Dussutour said. “But habituated ones survived.” They also quickly started extending out across their salty surroundings to hunt for food.

What that means, according to Dussutour, who described this unpublished work at a scientific meeting in April at the University of Bremen in Germany, is that a slime mold can learn—and it can keep that knowledge during dormancy, despite the extensive physical and biochemical changes in the cells that accompany that transformation. Being able to remember where to find food is a useful skill for a slime mold to have in the wild, because its environment can be treacherous. “It’s very good it can habituate, otherwise it’d be stuck,” Dussutour said.

More fundamentally, she said, this result also means that there is such a thing as “primitive cognition,” a form of cognition that is not restricted to organisms with a brain.

Scientists have no idea what mechanism underpins this kind of cognition. Baluška thinks that a number of processes and molecules might be involved, and that they may vary among simple organisms. In the case of slime molds, their cytoskeleton may form smart, complex networks able to process sensory information. “They feed this information up to the nuclei,” he said.

It’s not just slime molds that may be able to learn. Researchers are investigating other nonneural organisms, such as plants, to discover whether they can display the most basic form of learning. For example, in 2014 Monica Gagliano and her colleagues at the University of Western Australia and the University of Firenze in Italy published a paper that caused a media frenzy, on experiments with Mimosa pudica plants. Mimosa plants are famously sensitive to being touched or otherwise physically disturbed: They immediately curl up their delicate leaves as a defense mechanism. Gagliano built a mechanism that would abruptly drop the plants by about a foot without harming them. At first, the plants would retract and curl their leaves when they were dropped. But after a while, the plants stopped reacting—they seemingly “learned” that no defensive response was necessary.