Octopuses: what science discovered that changes everything you thought you knew

There is a moment that every diver with a certain amount of experience has lived. You're looking at a sandy or rocky bottom, not seeing anything in particular, and suddenly something moves. A texture that didn't quite fit. A colour that wasn't exactly the same as the floor. And then you see it: an octopus that had been there the whole time, watching you.

That moment of "how did I not see that?" is the best possible introduction to what we're going to explore in this post. Because the octopus is not simply an animal that camouflages well. It is one of the most neurologically sophisticated living beings on the planet. And the science of recent years has discovered things about them that completely change the way we understand what intelligence actually is.

And it does all of this in a way entirely independent of us.

It doesn't have one brain. It has nine.

When we talk about octopus intelligence, the first mistake is to imagine it like ours.

An octopus has approximately 500 million neurons — a number comparable to that of a dog. But this is where any similarity to neural systems we know ends: two thirds of those neurons are not in the brain. They're in the arms.

Each of its eight arms has its own nerve ganglion — a local neurological processing centre with around 40 million neurons each. More neurons than a frog has in its entire body. That makes each arm something that functions, in practice, as an independent brain.

What this means is revolutionary: when an octopus extends an arm toward a crab, that arm makes its own decisions. It feels, processes, acts — without needing permission from the central brain. The central brain is not sending detailed instructions like "now rotate 23 degrees, now grip with sucker number 4". It's sending something more like a general intention: "get that". How it gets it, the arm works out for itself.

The experiments are overwhelming: an octopus arm severed from the body — literally amputated from a dead animal — continues to react to stimuli, continues to try to grasp objects, continues to coordinate its suckers. The intelligence did not die with the animal. It was still in the arm.

A system like this solves one of the great problems of neurological design: speed. When you have eight arms with millions of suckers each, coordinating every movement from a single central brain would create an enormous bottleneck. The octopus's evolutionary solution was to decentralise intelligence. There is no boss — there is a network.

Scientists working in robotics and artificial intelligence have spent years looking to octopuses for inspiration precisely because of this. Distributed systems, without rigid hierarchy, are more resilient, more adaptable and more efficient in complex environments. The octopus has been doing this for 300 million years.

The brain is surrounded by the oesophagus — and that's a problem

If the above was already strange, this is simply absurd.

The central brain of an octopus is donut-shaped. And the oesophagus — the tube through which food passes — goes through the hole of the donut. The brain literally surrounds the oesophagus.

The practical consequence is that octopuses cannot swallow large objects. If a piece of food is too big, it can cause brain damage as it passes through. This is why octopuses shred and break up their food before swallowing — not out of culinary preference, but because their brain is in the way.

Evolution produced this because the ancestor of the octopus was a simpler animal with a smaller nervous system. As the brain grew, it simply grew around the structure that was already there. Nobody redesigned the system from scratch. It is one of the clearest examples that evolution is not elegant engineering — it is improvised engineering that happens to work.

They are colour-blind. And yet they change colour with impossible precision.

This is probably the most unsettling data point in this entire post.

Octopuses do not have colour-sensitive photoreceptors in their eyes. They are functionally colour-blind — in the strictest sense of the word, they should not be capable of distinguishing colours.

And yet they produce camouflage of chromatic precision that leaves you speechless. They become exactly the shade of orange of a sponge, the exact stippled pattern of a coral, the mottled beige of sand with its variations of brightness and texture. How?

The answer science is pursuing — still not definitively confirmed, but with growing evidence — is that octopuses see colour through their skin.

Their chromatophores — the pigment cells that control colour — contain proteins called opsins, which are sensitive to light. The same proteins that in vertebrate eyes allow colour vision. In the octopus, those proteins are distributed across the entire skin.

The hypothesis is that the octopus's skin functions as a distributed light sensor — that the animal literally processes light information directly from its body surface, without needing the eyes for this. The skin sees. Or something close to seeing.

If this is confirmed, we would be looking at one of the strangest sensory systems in the animal kingdom: an animal that perceives colour without being able to see it in the conventional sense.

The camouflage system, moreover, operates across three simultaneous layers:

Chromatophores control the pigment. They are ink sacs connected to muscles that contract or relax to expand or compress the cell, changing the visible colour. An adult octopus can have more than a million active chromatophores working simultaneously.

Iridophores control brightness and iridescence — that metallic or nacreous quality you see in certain parts of the body. They work through light interference, not pigment.

Muscular papillae control the 3D texture of the skin — that ability to appear smooth or rough, flat or covered in bumps and protrusions. An octopus can go from smooth as glass to rough as tree bark in fractions of a second.

All three layers act in a coordinated way, in real time, processing sensory information from the environment and translating it into camouflage patterns in milliseconds. It is one of the fastest information-processing systems in the animal world.

They edit their own genetic material — in real time

This is the most recent finding and possibly the most astonishing. Published in the journal Cell in 2023, a study from the University of Chicago and Tel Aviv University revealed something that until then had only been seen in very limited form in some insects: octopuses edit their own RNA in response to temperature changes.

To understand what this means: DNA is the permanent instruction manual of an organism. RNA is the messenger that translates that manual into proteins — into the actual components with which the body functions. Normally the process is fairly faithful: RNA copies the DNA and produces the proteins that DNA specifies.

Octopuses do something different. When the water temperature changes, they edit the RNA on the fly — modifying the message before the protein is produced, changing the type of protein that gets built without touching the original DNA.

In the study, when the temperature dropped, octopuses activated more than 13,000 RNA editing sites in their nervous system within a matter of hours. The result: different neural proteins, specifically designed to function in cold water. The nervous system reconfigures itself in real time to adapt to the environment.

Humans have millions of RNA editing sites, but they affect less than 3% of our genes. Octopuses edit up to 60% of their neural RNA messages. It is a genetic plasticity that no known vertebrate can match.

The implication is profound: the octopus does not wait for slow evolution to modify its DNA over thousands of generations to adapt to cold. It does it itself, within hours, within its own life cycle. It is a form of adaptation that redefines the boundary between what is fixed and what is flexible in biology.

They dream. And they do it in colour.

In 2021, researchers at the Federal University of Rio Grande do Norte in Brazil published a study that sent shockwaves through the scientific world. They had filmed octopuses sleeping and discovered that they alternated between two clearly distinct sleep phases.

The quiet sleep phase: pale, uniform skin, closed pupils, long and stable episodes. Similar to non-REM sleep in vertebrates.

The active sleep phase: this is where everything becomes strange. The skin starts changing colour and texture rapidly and dynamically. The eyes move. The arms contract. The muscles of the mantle twitch. And all of this happens in a way completely disconnected from the surrounding environment — the octopus does not react to what is around it, only to what is happening inside its own nervous system.

In 2023, the Okinawa Institute of Science and Technology confirmed this with greater depth: during that active phase, the neurological activity of the octopus brain is indistinguishable from its activity when awake. The same pattern. The same intensity.

That is exactly what happens during REM sleep in vertebrates — the phase in which humans dream.

Are octopuses dreaming?

The honest answer is that we don't know with certainty. We can't ask them. But if they are dreaming, researchers have a hypothesis about what those dreams are like: short and visual. Each active sleep episode lasts between 40 and 60 seconds. If there are dreams, they would be something like rapid, fragmented images — not long narratives like human ones.

What we do know is that two-phase sleep — quiet and active — evolved completely independently in octopuses and in vertebrates. Two lineages that diverged 550 million years ago arrived at the same solution for something we still don't fully understand.

They live briefly and die by design

Octopuses have short lives. Most species live between one and two years. And that life cycle has a mechanism that is, from a human perspective, deeply unsettling.

When a female octopus lays her eggs — up to 200,000 in some species — she stops eating. Not for lack of food. The feeding mechanism is actively switched off. During the weeks she guards the eggs, ventilating them and protecting them from predators, her body begins to consume itself. When the eggs hatch, the mother dies.

Males die weeks after mating, through a similar process of accelerated deterioration.

This process is not accidental or an evolutionary flaw. It is an active mechanism controlled by the optic glands — structures equivalent to the pituitary glands of vertebrates. If those glands are removed, the female starts eating again, abandons the eggs and can live for months more.

Why did such a system evolve? The most widely accepted hypothesis is that the resources the adult would consume competing directly with its own offspring are more valuable to the species if channelled entirely into protecting the eggs, then ceding the territory to the next generation. A brutal solution. A solution that works.

Why the encounter underwater is different now

If you have dived with octopuses before reading this, you probably experienced them as curious or fascinating animals. If you dive with them after reading this, the experience is different.

When an octopus looks at you — and octopuses do look, with that horizontal, calm gaze that gives the feeling of being assessed — what lies behind those eyes is a neurological system distributed throughout its entire body, processing information in parallel at impossible speeds, building in real time a response to the environment that includes your presence.

When it changes colour in front of you, it is executing one of the most sophisticated information-processing systems in the animal world. When you see it motionless in a corner of the seafloor, it may be sleeping. And if it is dreaming, it is experiencing something — what exactly, we don't know — in that mind distributed across nine simultaneous processing centres.

You encounter octopuses in almost every BTO destination. In Bali, on the sandy floors around Amed and between the crevices of the USAT Liberty. In Komodo, on the rocky floors of Batu Bolong. In the wrecks of the Red Sea. In La Paz, among the life-covered wrecks of the area.

The next time one looks at you, remember that it has more neurons in one arm than a frog has in its entire body. And that arm is thinking for itself.

Underwater photography and the octopus: the most difficult and most rewarding subject

If you do underwater photography, the octopus is the animal that will teach you the most about patience and anticipation.

Active camouflage: the same system that makes octopuses fascinating makes them photographically challenging. When camouflaged, it is invisible. When it decides you've spotted it and begins to move, it changes colour while moving — which means the correct exposure shifts constantly.

The behavioural window: octopuses have moments when they display active behaviour — hunting, exploring, changing colour defensively — and moments when they simply stay still waiting for you to leave. The difference between an archive shot and a photograph that tells a story is finding that window of active behaviour.

Wide-angle and macro: the octopus is the animal that most justifies carrying both options on the same dive. A large octopus in its environment, with active camouflage and the background visible, calls for wide-angle. The details of the skin — the texture of the papillae, the colour of the chromatophores, the horizontal gaze — call for extreme macro.

In the photography workshop of every BTO expedition, the octopus always features in the briefings. Not as a guarantee — there are no guarantees with wild fauna — but as an example of the kind of slow, deliberate observation that separates the photographs you remember from the ones you forget.