One of the most compelling things about octopuses is their intelligence, perhaps unique among invertebrates. They are of the phylum Mollusca, a group that also includes clams and oysters among a great many others, and the class Cephalopoda (the name derives from the Greek for “head-feet”), a group that includes octopuses, squids, cuttlefish and nautiluses, all of which have have been the subject of much research in terms of neurology and behavior alike, and all of which demonstrate at least some capacity to learn.
The brain of the octopus is not centralized as ours is. Instead, there is a portion of the brain surrounding the esophagus and a large lobe behind each eye. The rest – about 2/3 to 3/5 of the total processing power – is distributed among the eight arms. To a point, each arm can act independently and can retain movement for a time even after separation from the animal. The arrangement has been described using computers as analogy: one researcher likened the difference in neural organization between octopuses and ourselves to the difference between the internet and a computer’s CPU.
The arms are, of course, covered in suckers. The suckers are powerful, and together give an octopus enough strength to move an object up to 14 times its own weight. They can operate independently of one another, and can be used to pinch in addition to creating a bond via suction. Their motor control is fine enough to untie knots.
Each sucker also has complex chemical receptors that can ‘taste’ whatever comes into contact with them. The octopus can use this ability not only to distinguish prey items from non-prey, but also to distinguish individuals. This is not surprising given the sheer quantity of these receptors: about 10,000 per sucker.
The skin of the octopus is remarkable, too. It has additional chemical receptors that allow the animal to ‘smell’ passing molecules in seawater. It is also covered in chromataphores, specialized cells that react to light and enable the octopus to change color, and papillae connected to tiny muscles beneath the skin that allow it to change texture. These properties help to make the octopus a master of disguise.
An octopus can make itself blend with any surface, seemingly becoming a part of the reef, rock or sand around it. But it has more elaborate ruses, too: depending on the species, an octopus can mimic as many as 15 different organisms, including lionfish, sea snakes, jellyfish and various flounders. This ability is used as a primary defense mechanism. In order to accomplish this, the octopus changes its shape, color and texture to conform to the animal it is impersonating and then mimics the behavior of that animal. It is an amazing feat to witness. Such mimicry naturally requires some decision-making on the part of the octopus: it must analyze a threat and determine which of the animals in its repertoire is most likely to deter that threat.
This brings us back around to intelligence, always a somewhat tricky topic when referring to other species. Scientists don’t always agree about what constitutes intelligence, and in the case of the octopus there is a huge difference in the organization of the brain, making it even more difficult to accurately gauge. The last common ancestor that we share is likely a worm of some kind, meaning that intelligence in octopuses evolved independently from our own, Consequently, it is so different as to be completely alien to us. Attempts to bridge that gulf are ongoing, but it is clear that what we don’t know about these creatures far outweighs our knowledge of them.
Studies have shown that octopuses are excellent problem-solvers. They use tools, and sometimes carry them along for use at a later time; they have been seen taking coconut shells with them to hide in should a predator come. They can manipulate objects and solve puzzles, and they become much faster at solving a given puzzle once they have already done it, indicating that they remember how to perform the task.
This, combined with their ability to squeeze through any space smaller than their beak, makes them extremely difficult to keep: they are notorious escape artists. More than one octopus has managed to find its way from an aquarium back into the ocean, although more often the animal simply dries out and dies. There are also many stories of octopuses slipping out of their tanks to snack on fish or crustaceans from a neighboring tank and then returning to their dens, leaving their keepers wondering what happened to the creatures in the other tank.
These stories, along with the other evidence of intelligence in octopuses, have led some researchers to believe that the octopus has what is called ‘theory of mind’, meaning that not only is the animal thinking, but it has an awareness that other creatures besides itself also think. This is, however, a nearly impossible thing to test and its presence in nonhuman animals remains controversial.
But if we open ourselves to the possibility that this quality may exist among other animals, where might we find it? Primates certainly demonstrate some level of this. So do elephants. And most dog lovers will argue that their canine companions do, too.
But an invertebrate? An octopus? The idea seems somewhat incredible. We are faced with an intelligence utterly unlike our own, and with which we have no way to communicate in any meaningful fashion. Our ability to test the limits of that intelligence is itself limited by our lack of understanding. In the end, we simply do not know. And we may never know. But that does not mean that we won’t keep trying.