FACTS: The octopus has three hearts and nine brains—the strangest animal

A Central Brain That’s a Minority in Its Own Head

The octopus’s central brain, located between its eyes, accounts for only one-third of its total 500 million neurons—a number comparable to that of a dog. The remaining two-thirds are distributed throughout its eight arms, organized into axial nerve cords that run the entire length of each limb. Each arm has its own ganglion, a mass of nervous tissue capable of processing sensory information and generating autonomous movements.

It is this architecture that gives rise to the popular expression “nine brains”: one central brain and eight brachial nerve centers. Scientifically, the question of whether these ganglia deserve the title of “brains” is still debated—but what is certain is that each arm can act independently, process local information, and execute complex movements without waiting for instructions from the central brain.

Arms That Think and Act on Their Own

The most striking evidence of this nervous autonomy? A severed arm continues to react to stimuli for some time after being separated from the body. It retracts when pinched and reaches out for food. The central brain has nothing to do with it—it is the brachial ganglion itself that processes the information and decides on the response. In 2020, a study published in PubMed showed that the octopus’s central brain uses sensory information from the arms to guide complex movements—but that the arms also have the ability to act without it.

This organization resembles a federation rather than a monarchy: the central brain is the loudest voice, but not the only one. Each arm negotiates in real time, processes information locally, and contributes to the overall decision. It is a distributed control architecture that allows for extraordinary behavioral flexibility—and one that robotics engineers are now trying to replicate in soft robots.

Soft robotics draws direct inspiration from the octopus’s arms to create robots capable of navigating narrow and unpredictable spaces. Nature solved this engineering problem millions of years ago. We’re just catching up.

Memory, Learning, and Individual Personality

According to National Geographic’s official fact sheet, the octopus is considered the most intelligent known invertebrate. It is capable of observational learning—watching a fellow octopus solve a problem and replicating the solution—classical associative learning, spatial memory, and even tool use. Observations in the wild have documented octopuses collecting coconut shells to carry them away and assemble them into a shelter—a form of planning that involves transporting something whose usefulness is not immediate.

Researchers have also documented individual personalities in octopuses: some are curious and exploratory, while others are shy and cautious. In repeated experiments with the same individuals, these behavioral differences persist over time—which aligns with the scientific definition of individual temperament. One octopus is not interchangeable with another.

Camouflage: A Neurological Masterpiece

The octopus’s skin is a neurological display screen of the utmost sophistication. It contains chromatophores (pigmented cells controlled by muscles), iridophores (reflective cells), and papillae (which allow it to change texture). In a matter of milliseconds, the octopus’s brain can reconfigure its entire body surface to mimic a rocky seabed, coral, sand, or even another animal. This ability is all the more remarkable given that the octopus is likely color-blind—it perceives the world in shades of gray but manages to reproduce colors with astonishing precision, perhaps thanks to skin photoreceptors.

The National Geographic Society describes this system as “body manipulation”: texture, color, and shape change simultaneously. Some octopuses mimic flat octopuses, venomous fish, and sea urchins. The animal becomes its environment—a mastery of disguise that even the best human actors cannot match.

A color-blind animal that mimics colors with astonishing precision. If that isn’t evolutionary ingenuity, I don’t know what is. Nature doesn’t need perfection—it needs efficiency. The octopus is the ultimate demonstration of this.

Convergent Intelligence, Evolved Twice

The intelligence of octopuses and that of vertebrates (mammals, birds) evolved independently along two evolutionary lineages that diverged approximately 500 million years ago. This is known as convergent evolution: two different solutions to the same problem—surviving in a complex world. Neuroscientists use octopuses as a model to understand which brain structures are truly essential for intelligence, and which are merely characteristics specific to the vertebrate lineage.

The octopus’s brain is organized in a toroidal pattern—forming a ring around the esophagus—which means that if an octopus swallows something too large, it risks injuring its brain. This unique anatomical constraint exists nowhere else in the animal kingdom. It shows that the octopus has developed its intelligence within a bodily framework radically different from our own—and that intelligence can flourish in architectures we would never have imagined.

A Short Life for Such Sophistication

This is perhaps the most unsettling fact of all: octopuses live, on average, one to two years. All this sophistication—the nine brains, the three hearts, the problem-solving intelligence, the neurological camouflage—is condensed into a brief existence. Unlike intelligent mammals (dolphins, elephants, great apes) that live for decades and pass on cultural knowledge, the octopus starts from scratch with each generation. Each individual reinvents on its own behaviors that its parents may have discovered.

Some scientists believe that this short lifespan is the reason the octopus has not developed a social culture—there isn’t enough time to form stable groups and teach. Others argue that the octopus’s solitude is precisely what has selected for such a highly developed individual intelligence: alone in the world, each octopus has had to learn to manage everything on its own.

A year or two to live, and yet capable of opening jars, camouflaging themselves as rocks, and solving mazes. This raises a mind-boggling question: what would octopuses be like if they lived ten years? Twenty years? The brevity of their lives may be the only reason they haven’t already surpassed us.

A mirror held up to our definition of consciousness

The octopus isn’t just a strange animal. It’s an invitation to rethink what it means to be conscious, intelligent, and even alive in a complex way. Its distributed nervous system, its three specialized hearts, its blue blood, and its neurological camouflage are not merely exotic curiosities—they are evolutionary solutions to real problems, developed independently of our own lineage. They show us that biology can take paths we never imagined.

Fertile Ground for the Science of the Future

Researchers in robotics, neuroscience, regenerative medicine, and artificial intelligence are all looking at the octopus with growing admiration. Its autonomous arms inspire soft robots, its camouflage inspires adaptive materials, and its distributed neural architecture inspires new models of information processing. The ocean’s strangest animal is also, perhaps, one of the most valuable teachers in contemporary science.

By Maxime Marquette, columnist

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