The Insane Biology of: The Octopus

In many ways, the octopus is as close to alien life as we may ever see. Few creatures in the world are as remarkable and bizarre. A part of a class of animals called cephalopods, they are among the most intelligent and most mobile of all the invertebrates. They live in every ocean in the world, in the deep sea, in kelp forests, in coral reefs, along rocky shorelines, and they are as diverse as the habitats they live in. They can be massive or absolutely tiny. Some species are venomous and some are just downright strange. In any given moment, they can appear spiky or they can appear smooth. They are so different from us that most of their 500 million neurons are not in their brain but in their arms, which can smell and taste and even think, and so intelligent that their cognitive ability matches that of many large-brained vertebrates. They have left scientists stunned about how a creature so far from us on the evolutionary tree could evolve such complex behaviors, their intelligence emerging in an entirely novel and independent way from our own. So how did the octopus become so biologically complicated, an island of complexity in the sea of invertebrate animals? Just how intelligent are they, and how can studying them reveal information about our own minds? Cephalopods have been around for a long time. Fossil records show that they evolved over 500 million years ago, long before any fish, reptiles, or mammals ever appeared on Earth. The early ancestor of the octopus was quite small and had a shell, which it used to protect itself as it crawled along the ocean bottom. Cephalopods are, after all, members of the mollusc phylum, a group of creatures that are usually slow and simple, with soft bodies and a hard, protective shell, like snails, clams, and oysters. But around 140 million years ago, the lineage that produced the octopus lost their shells, making them nimble, agile creatures, but in the process also made them rather vulnerable. Survival of these soft-bodied creatures for so many millions of years therefore seems unlikely in a sea full of dangerous, hungry predators. But this vulnerability and selective pressure may be precisely what has allowed the octopus to become the remarkable creature we know today. Because an octopus has almost no hard parts at all, except its beak, it can squeeze through any hole as long as it's larger than its eyeball. This allows the octopus to hide in very small crevices, a certain evolutionary advantage when escaping large predators like sharks or dolphins. But the soft-bodied octopus evolved an even more clever way of evading detection. They are masters of disguise! Watching this clip of an octopus, you can see just how quickly and drastically it can change colors. In slow motion reverse, you see the color change spread across its body. The 3D texture of the skin also changes to match the surrounding seaweed and coral. In the blink of an eye, it has almost completely blended in with its surroundings. Cephalopod camouflage is among the most dynamic in the animal kingdom, and relies on a system of extremely sophisticated tissues. Chromatophores are organs that are speckled across the skin of the octopus, like freckles. They contain tiny pigment-filled sacs, like little balloons full of different colored dye, which can be black, red, or yellow. The pigment sacs are surrounded by radial muscles, which can stretch the sac to reveal the pigment's color. Just like balloons full of dye, when stretched, their pigment color appears bright and vibrant. Depending on which sets of sacs an octopus opens or closes, it can produce patterns such as bands, stripes, or spots, helping to turn itself into a rock, a coral, or a kelp in an instant. But, if the octopus needs to produce colors outside of black, red, and yellow, it uses another layer of reflective structures in their skin called iridophores. They are stacks of very thin cells that lay beneath the chromatophores. They contain a protein called reflectin that bounces certain wavelengths of light back out. They are responsible for the metallic blues and greens that appear to shimmer on the skin of the octopus. Beneath that layer is yet another layer of reflective tissue called lucifers. These reflect ambient light, usually producing white hues. By combining reflection from the iridophores and lucifers with the correct patterning of the chromatophores, the octopus can create a very convincing copy of its surroundings. But the octopus has one more trick up its sleeve, allowing it to disappear in plain sight almost completely. Using a structure called papillae, it can change the texture of its skin, creating ridges and bumps that rise and fall. This helps the octopus match its surroundings even better. With all these tools, the shell-free, soft-bodied octopus has been able to deceive an ocean full of predators for millions of years. But, their survival has not hinged on these camouflage properties alone. It's the way they're controlled that is perhaps an even more compelling survival tool. When an octopus travels along the seafloor, they have to assess the background and modify their camouflage constantly. They are making decisions at a rapid pace. One researcher observed an octopus changing its camouflage 177 times in one hour. Octopus's camouflage reaction times are faster than any other animal's, up to 200 milliseconds, as fast as the fastest blink you can do. But, despite doing so much with color, the octopus, and almost all cephalopods, are surprisingly thought to be colorblind. How can they match colors they can't even see? In 2015, the answer to this question started to be uncovered. Researchers found that the skin of an octopus is sensitive to light due to photoreceptor genes active in the skin. Even when the skin was detached from the body, it could respond to light and change the shape of its chromatophores. Scientists realized that an octopus can see with not just its eyes, but also its skin. But as the octopus body was evolving its color-changing defense mechanisms when it lost its shell 140 million years ago, another transformation occurred, the development of its large brain and nervous system. The photoreceptor genes in the skin work in connection with the octopus's large and complex brain. The octopus can change color so fast because the octopus controls its chromatophores neurally. Other animals that can change color, like chameleons for example, take much longer because their color change is hormonally controlled. Hormones take time to get into the blood and distribute around the body. A color change can take over 20 seconds when controlled this way. Some researchers believe that color change in the octopus may be like breathing or blinking for us, something it can choose to do, but also something that can happen involuntarily. It can have awareness from its eyes and brain, but also throughout its body. The octopus nervous system is large like ours, but built with a different relationship between body and brain altogether. The common octopus has around half a billion neurons in its body. For comparison, humans have about 100 billion. Most invertebrates usually have much less. Snails have only 20,000. But cephalopods like the octopus score in the same range as many vertebrates, like cats, dogs, and parrots, more than any other invertebrate. And of their 500 million neurons, only a third are found in their brain. The majority are found in their eight arms. And as strange as it sounds, this allows the octopus to, in a way, think with its arms. For a long time, scientists have known that a severed octopus arm can respond to stimuli an hour after being separated from the central brain. But a paper last year began to reveal the extent of this autonomy. Using video modeling, they observed the octopus as it explored objects in its tank and looked for food. The program quantified movements of the arms, tracking how the arms worked together in synchrony, suggesting direction from the brain, or asynchronously, suggesting independent decision making in each appendage. And they found that in the flow of information from the environment to the octopus, some information bypasses the central brain entirely. The suckers and arms can, in a way, think for themselves, allowing the octopus to analyze its environment extremely quickly and react with matching speed. Along with skin that can perceive and change color on its own, the relationship between brain and body in the octopus is full of blurred lines. And on top of this unusual neural layout and strange body autonomy, cephalopods are smart, extremely smart. And this is really what gives the octopus its alien-like status. They are so far from any other intelligent life on the tree of evolution, but still compete with vertebrates in their raw cognitive ability. Evolution invented intelligent life not once, but twice, in two completely different ways. In the evolutionary tree of life, we sit upon the branch of mammals. Nearby are the fish, reptiles, birds, and amphibians, the other members of the larger classification of vertebrates. This group is where we see all of the intelligent life we normally think of. Humans, primates, dogs, cats, dolphins, and some birds. When we collect these animals and trace back to our common ancestor, it was likely a lizard-like animal that lived around 320 million years ago. Like us, this animal would have had a backbone, four limbs, a head, and a skeleton. It would have walked around, well-adapted to land, and had a well-developed central nervous system. But to find where we split from the octopus, we have to travel much further down the branches, to around 600 million years ago. The creature we find there is a simple, flat worm. It had an extremely basic nervous system, and no inklings of what we would consider intelligence. As the evolutionary tree branched and diverged, intelligence blossomed on our branch of vertebrates, and totally separately in the cephalopods. And with the cephalopods evolving before any of the intelligent vertebrates, it's likely that they were the first intelligent animals that appeared on Earth. But what actually is intelligence? How can we identify, or even measure such a thing in an animal so different from us? In humans, intelligence is commonly defined as the ability to think abstractly, understand, communicate, problem-solve, learn, form memories, and plan actions. This is usually measured by intelligence tests which can be given a numerical value. But we can't give a standardized test to an octopus. We can only observe their behaviors. Why the cephalopods? Well, they're the most interesting mollusks in terms of behavior. No question. To learn more about the depth of octopus intelligence as researchers currently understand it, I spoke with Jennifer Mather, professor in the department of psychology at University of Lethbridge, and scientific advisor for the film My Octopus Teacher. Pretty well every learning task you give them, they can do. Short-term, long-term, spatial memory, object perception, you know. But it's more than learning. They also go in for planning. And planning is not so obvious. And one of the famous examples is what's been called the coconut-carrying octopus. So the octopus is going off to a place where there's no shelter, and it takes these coconut halves with them. And when it wants to stop and rest, it picks them up and brings them up and goes like this around it. It's amazing. Some scientists argue that this behavior is a rare example of composite tool use, a behavior previously thought to only exist in humans, some primates, and some birds. And it may be evidence of complex intelligence for two reasons. First, this tool use might represent a behavioral innovation allowing octopuses to protect themselves in areas where they can't otherwise hide. Second, because the coconut shells are transported with great effort to meet future needs, this behavior might indicate an octopus' planning ability. The octopus has to imagine the future and connect the dots between past events, current actions, and future events, which is not a simple task. Octopuses also do well in memory tests and can differentiate between different people even when they're wearing the same outfit. And in a study done by Professor Mather, the common octopus has also been shown to be extremely playful. I would describe them as extremely exploratory, sort of like a five-year-old kid, taking stuff apart, going off and feeling around the landscape, just grabbing more information. Play is often defined as a behavior that is not necessary for survival, done on purpose, but seemingly for pleasure. The action is often repeated, exaggerated, and carried out when the animal is adequately fed, healthy, and not under stress. We figured that the animals were more likely to play if they were safe and bored. So we set up octopuses in an aquarium with a place to hide and nothing else. And then we got a pill bottle and put enough water in it that it floated at the surface. Also in the mix was a water intake pump for the aquarium that the researchers hadn't necessarily intended to be part of the experiment. It created a current that pushed the pill bottle across the top of the tank, which sparked the curiosity of some of the octopuses. So we did this with six animals, okay? In two cases, the pill bottle came across like this. The octopus shot a jet of water at it, which meant that it went back towards the water intake and it came back again. If an octopus did this once, or even twice, it wouldn't be experimentally significant. But a few carried out this behavior so many times that it couldn't be ignored. One of them did this, I think it was 14 times, and one of them did it 21 times. It was the marine equivalent of bouncing the ball. In addition to helping establish motor coordination, play in most species is largely needed for social purposes, for establishing rank, for learning social rules, or for social bonding. And due to its complexity, play is considered to be almost exclusive to mammals, with a few exceptions in other vertebrates like some birds. But the octopus is a solitary creature. It has no social bonds, no social hierarchy. It makes us rethink the evolutionary reasons for play. In fact, much of our idea of intelligence is based on the idea that it evolved out of a social need. For decades, scientists have wondered about the origins of intelligence, and have tried to understand why certain animals evolved intelligence and others did not. The social intelligence hypothesis is the often favored hypothesis for the evolution of complex cognition. It's the idea that intelligence evolved due to the demands of group living, such as maintaining complex and enduring social bonds, deception, cooperation, or social learning. When most of the animals we think of as smart, humans, primates, dogs, dolphins, began living in groups, there became a need for more complex behaviors, and therefore a bigger, more complex brain. But this theory can't explain why intelligence evolved in cephalopods. A different theory must exist for these non-social creatures. You see, our big problem with knowing the development of intelligence is that we know it from the mammals, from the primates, our relatives. So we know that this particular set of conditions sets us up for being intelligent. But then if we have another model, the octopus, then we have to say, okay, these conditions, being part of a social group, they're not necessary for intelligence. Perhaps the pressures of finding food and evading predation is enough for intelligence to blossom. This is the basis for the ecological intelligence hypothesis, which suggests that complex cognition evolved to meet the challenges associated with predation, foraging, and competitive pressures. And when the octopus lost its shell 140 million years ago, perhaps the pressure of predation was so high that outsmarting their attackers became the only way for it to survive. These two theories are not competing ones, but rather two explanations for two instances of intelligence on the tree of life. The octopus gives us a rare chance to investigate an alternate intelligence, an alien-like life form here on Earth. Where we once thought there was only one model for intelligence, we now know there are at least two, and who's to say how many more there could be, on this Earth or elsewhere. But despite the distance from us on the evolutionary tree, the octopus still lives inside the same grand experiment as we do. The Earth, the oceans, and the spinning wheels of evolution have crafted us both. They are not so much alien then, as much as a distant, distant relative. And by stepping aside from our human-centric view of intelligence, can we start to clearly see the infinite possibilities of cognition. The story of the modern octopus began so long ago, back when there was no life yet on land. But around this time, 500 million years ago, the oceans had begun to explode with life. This period, called the Ordovician, was known for its amazing diversity of invertebrates. And of these invertebrates, the massive, armored cephalopods were king. They dominated the seas for roughly 360 million years. The fossil records show an amazing array of creatures during this time, some we recognize, and some we definitely don't. Life was thriving, until something stopped nearly all of it in its tracks. To learn more about this period on the early Earth, and understand what nearly wiped out all of the animals in the planet's first mass extinction, you should watch Ancient Oceans on CuriosityStream. It's a two-part series that covers the Ordovician and Devonian periods, and explores the boom of animals then, and the subsequent mass extinctions. CuriosityStream is a streaming platform with thousands of high-quality documentaries like this one. 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