Jellyfish are brainless, but smarter than you'd think (2024)

A box jelly fish. Photograph: Dewald Kirsten

Jellyfish, those almost alien inhabitants of the deep, are not the simple creatures we once thought. A groundbreaking study from the University of Copenhagen reveals that these mesmerizing animals possess an unexpected intelligence, challenging our understanding of both their brains and our own.

In the world of marine biology, jellyfish have long been considered the humble denizens of the deep, with a reputation for simplicity and limited learning abilities. However, a recent study published in the journal Current Biology is poised to turn all of that upside down.

Caribbean box jellyfish, known for their venomous stings, have taken center stage in this scientific revelation. Despite having just 1,000 nerve cells and no centralized brain, they’ve showcased a remarkable capacity for complex learning. This discovery promises to reshape our fundamental understanding of the brain and could hold crucial insights into human cognitive functions and the processes underlying dementia.

Jellyfish, which have roamed our oceans for over 500 million years, were traditionally thought to be basic organisms with minimal learning capabilities. The prevailing scientific notion has been that more advanced nervous systems correlate with higher learning potential among animals. Yet, jellyfish and their cnidarian relatives were among the earliest animals to develop nervous systems.

Anders Garm, neurobiologist and professor at the University of Copenhagen in Denmark, has dedicated over a decade to researching box jellyfish, has shattered these preconceptions. These fingernail-sized creatures residing in Caribbean mangrove swamps, employ their sophisticated visual system made up of 24 eyes to hunt tiny copepods among the roots. “It was once presumed that jellyfish can only manage the simplest forms of learning, including habituation — the ability to get used to a certain stimulation, such as a constant sound or constant touch,” Garm says. “Now, we see that jellyfish have a much more refined ability to learn — and that they can actually learn from their mistakes… [and] modify their behavior.”

A crucial aspect of advanced nervous systems is the ability to change behavior based on experience—a form of memory and learning. As box jellyfish approach mangrove roots, they must precisely time their maneuvers to catch prey without colliding with obstacles. The research found that contrast—how dark the root appears in the water—serves as the key factor in distance assessment, allowing the jellyfish to swim away at precisely the right moment. What’s more intriguing is that this relationship between distance and contrast evolves daily due to environmental factors, and the jellyfish learn from these changing patterns.

Surprisingly, these creatures, with a mere 1,000 nerve cells (compared to our brains’ roughly 100 billion), exhibit associative learning at a pace similar to advanced animals like fruit flies and mice. This finding challenges conventional beliefs about the capabilities of animals with simple nervous systems.

The research also sheds light on where this advanced learning occurs within jellyfish. This discovery opens new opportunities to study the precise changes that occur in a nerve cell when it’s involved in advanced learning. “We hope that this can become a supermodel system for looking at cellular processes in the advanced learning of all sorts of animals,” says Garm. “We are now in the process of trying to pinpoint exactly which cells are involved in learning and memory formation,” he said. Pinpointing the exact mechanisms behind jellyfish learning could have broad implications, potentially aiding our understanding of dementia and memory-related disorders.

While the study doesn’t claim to provide a cure for dementia, it offers a promising avenue for unraveling the complexities of memory, which could eventually lead to innovative approaches in combating this debilitating condition. Understanding the enigmatic and immensely complex brain is an astonishing journey, with countless possibilities waiting to be explored.

As Professor Garm aptly puts it, “There are unimaginably many useful possibilities in our quest to comprehend the brain and its mysteries.”