Earlier this year, Dussutour showed that slime molds can learn—at least, to a simple degree. She presented them with an obstacle course: To reach some food, they had to crawl over a bridge that was laced with repellents like salt or coffee. At first, the molds were clearly repulsed, and were slow to ooze across. With more repetitions, they became habituated; they got used to the chemicals, started ignoring them, and moved faster. And if Dussutour gave them a long timeout, and then reintroduced them to the bridge, they were just as reluctant to cross as they originally were.
Habituation is one of the simplest forms of learning, but slime molds show all its hallmarks. They get used to the chemicals with repeated exposure, and then become newly sensitized once exposure is withdrawn. Their behavior changes based on their experiences, and they retain a kind of primitive memory. “Most people thought that it was impossible for a cell to learn,” says Dussutour, “but we’ve tried this now with more than 2,000 slime molds. It can’t be an accident.”
Now, using the same bridge-crossing experiment, she has also shown that slime molds can transfer what they’ve learned by merging with each other. She brought naïve slime molds that had never encountered the repellent chemicals next to habituated ones that were already used to them. As is their wont, the molds fused. And those merged molds behaved as if they were habituated—they were quicker to cross the bridge than naïve individuals. Even if three naïve molds fused with a habituated one, the resulting entity still shows signs of habituation.