Learning Without a Brain

March 1, 2024
By Tara Haelle

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Caribbean box jellyfish are quite small and are able to learn to maneuver around the mangrove roots they live among. Credit: Jan Bielecki CC BY-SA 4.0

You would think it’s necessary to have a brain to be able to learn new things. But at least one brainless marine creature has shown scientists otherwise. For the first time, a jellyfish recently revealed its ability to learn from experience. Scientists shared their results of an experiment in which a Caribbean box jellyfish learned to identify and avoid obstacles.

Caribbean box jellyfish are tiny—one of the smallest jellyfish in the world. At barely the size of a blueberry, these cnidarians live among the mangroves of Central America and eat plankton. But they have remarkably sophisticated vision, with 24 eyes that help them maneuver the murky waters around mangrove roots to hunt their tiny crustacean meals. Their nervous system is dispersed throughout their body but they have no brain to process information received from their eyes and other sense organs.

Because these jellies are good navigators, scientists focused on this skill to see if they could apply knowledge from past experience to a new challenge. The researchers decorated a round tank with gray and white stripes to mimic the look of mangrove roots. Then the scientists watched a Caribbean box jellyfish swim through the tank for 7.5 minutes. At first, the jellyfish repeatedly bumped into the gray stripes, mistaking them for distant roots. But eventually, the jellyfish began avoiding the gray stripes. In fact, by the time the experiment ended, it pivoted away from the gray stripes four times more often than it did at the start and it hit the wall half as often. This is known as associative learning, where animals link sensory experiences—in this case, visual and touch—to behaviors. These findings raise questions about what other brainless creatures can learn too.