The Octopus: From Seeing with their Skin to Phenomenal Mimicry.

Approximately 600 million years ago, octopuses, cuttlefish, and squids - all of which are cephalopods - branched off from the lineage that would eventually lead to humans. The octopus’ lineage consists solely of invertebrates, including cephalopods and insects. While some insects, such as honeybees and ants, exhibit complex behaviors, their nervous systems are relatively small, with a maximum of one million neurons. However, cephalopods, particularly octopuses, are an exception to this rule, boasting approximately 500 million neurons, comparable to a dog’s brain, whereas human brains possess 16 billion neurons. Octopuses are unique creatures equipped with eight arms, each containing a mini-brain. They have a ring-shaped central brain, circulate blue blood, and are powered by three hearts. The smallest species, Octopuss arborescens, is about 2 inches long. The common octopus (Octopus vulgaris), found along the east coast of the U.S., grows up to about three feet long and the largest species, the reddish pink giant Pacific octopus (Enteroctopus dofleini), may grow to 18 feet in length.

The Earth, which is 4.5 billion years old, saw the emergence of life in the form of bacteria about 4 billion years ago. Animals appeared much later, almost a billion years ago. Octopuses and other cephalopods share a common ancestor from the Jurassic age, around 201.4 to 145 million years ago. This is when the two main cephalopod lineages diverged, one with eight arms including octopuses and another with ten arms including cuttlefish and squids. Prior to this divergence in the Jurassic age, the common ancestor had camera-like eyes with lenses, like our own, as do modern day octopuses. This suggests that two vastly different lineages developed large brains and similar vision capabilities. Despite being on completely different evolutionary paths, nature found two distinct ways to develop minds.

The skin of an octopus is akin to a 10-megapixel screen. Its outer layer, the dermis, contains chromatophores that hold color, iridophores that reflect certain light wavelengths, and leucophores that also reflect light. Despite most cephalopods reportedly being colorblind, an octopus’s skin can sense light and respond by changing its color. This discovery implies that an octopus can “see” with its skin. If the skin’s light sensing is connected to the brain, the animal’s visual skin sensitivity is also dependent on its eyes. If not, each arm might have its own independent vision. Even if the entire body can see, it appears to be in monochrome. However, a chromatophore might act as a filter over a light-sensitive cell, allowing a monochrome sensor to detect color if the organism has different colored light filters and knows which ones are in use at any given moment. Ultimately, the central nervous system is monochromatic, but to blend in with the background so amazingly, an octopus must be seeing in color with its skin to be able to match colors so well.

An interesting story of light is seen in the light producing symbiosis that has been extensively studied in the Hawaiian bobtail squid, and its relationship with the bacterium Vibrio fischeri. The bobtail has two light organs inside their mantle which houses the symbiotic luminescent bacteria. An example of quorum sensing, an act I discuss at length in my blogpost on Liquid Brains, where when enough of a common life form is present to make a quorum; with liquid brains it was with honeybees and a quorum was with getting enough, a quorum, of bees at a prospective new nest site before that site was chosen and the entire hive would then migrate to the new site. Within the bobtail squid, bacteria produce light by chemical reaction, but only if enough bacteria are around to join in. The bacteria achieve this by detecting the local concentration of an inducer molecule, which is made by the bacteria and gives each individual a sense of how many potential light producers are around. When the bacteria sense a quorum of themselves is around they start producing light, and when enough light is being produced, the squid housing the bacteria gains the benefit of camouflage. This is because the bobtail squid hunts at night when moonlight would normally cast its shadow down to predators below. Their internal glowing bacteria cancel out their shadow.

Camouflage is intrinsically linked to the process of visual perception. While it typically centers on the visual capabilities of various predators, in the case of octopuses, it also pertains to their own visual skills and the decision-making process involved in selecting a camouflage strategy. As such, the ability to modify camouflage requires the development of a method to swiftly analyze a visual scene, identify its key features, and apply an effective camouflage pattern. This represents an exceptional cognitive process that involves high-level decision-making. As just discussed above some, if not most, of the decision making is taking place at the skin level under control of mini-brains. For instance, the Cyanea octopus, found in the Pacific coral reefs, alters its appearance more than 150 times per hour while foraging for food daily. Each change is necessary as octopuses are mobile and continuously move into different visual environments. They can create patterns on their skin in as little as 200 milliseconds, which is equivalent to the speed of a human eye blink. Octopuses can sometimes mimic stones, algae, the ocean floor, and corals, for example. They can remarkably change their overall body shape, coloration and skin texture to match three-dimensional objects in the distant background.

In 2015, the first complete genomic sequence of an octopus was unveiled, and it’s astonishingly almost as large as that of humans. It also includes hundreds of genes specific to cephalopods. A significant number of these octopus-specific genes are expressed in their nervous systems, such as in their arm’s suckers, mini-brains, and central brain. This explains the diverse and unique cognitive abilities of these remarkable creatures. Additionally, octopuses engage in the highest level of RNA editing among all animal species, surpassing even humans. RNA editing is a process where, after a gene is expressed by copying its DNA template into RNA, a process known as transcription, the resulting RNA version of the gene is then cut and reconnected in various ways and locations. This process allows the animal to create a wide array of novel proteins using these edited RNAs as a guide. This is done through a process called translation, where RNA-encoded information is converted into specific types of proteins using the genetic code. This gives the octopus a significantly larger effective genome. These protein variations in the octopus’s nervous system can change the behavior of a given neuron by directly or indirectly altering its firing pattern. This provides the octopus with a multitude of ways to manipulate and control various abilities, such as its ability to see with its skin, adjust its camouflage accordingly, learn, and even think spatially.

Octopuses and other cephalopods' nervous systems are organized very differently from ours. Cephalopod literally translates to the brain on the foot. Their arms have not only the capacity to sense touch, but also detect chemicals as in smell or taste. Each sucker on an octopus' arm may have 10,000 neurons to handle taste and touch. Hunting and foraging makes good sense for the exploratory curiosity side of the octopus psyche especially their engagement with novel objects.   There seems to be a kind of mental surplus in the octopus. The capacity for several types of learning is also seen in both our own and the vastly different octopus lineage. Learning by attending to reward and punishment, by tracking what works and what does not work, seem to be invented independently several times over the course of evolution. There are also more subtle psychological similarities. Octopuses, like us, seem to have a distinction between short-term and long-term memory. Octopuses can use tools: Octopuses can manipulate objects in their environment to achieve their goals. For instance, they can use rocks or shells to cover the entrances of their dens, protecting them from predators. They can also use coconut shells as portable shelters, carrying them around and hiding inside them when needed. Some octopuses have even been observed using sponges to wipe off dirt from their bodies.

Additionally, Octopuses can learn and remember the layout of complex environments, such as mazes or novel aquariums. They can use visual cues or landmarks to find their way around and locate food or shelter. In one experiment, octopuses were able to guide one of their arms through a maze, where the octopus’ arm and its hundreds of suckers could not feel or smell its way to the food, but had to be guided to the food by the observation of the limb and food via its camera eyes and the central brain, demonstrating that they can control their limbs independently and conduct them centrally while at the same time allow the limbs the freedom to explore on their own. I am tempted to call the octopus as having a Glassy Brain, that is, it is mostly solid, a large central nervous system, but at the same time having a liquid aspect, much like glass, which is technically a liquid, with the freedom displayed by their highly innervated and exploratory arms and suckers.

Octopuses can apply their knowledge and skills to novel situations and challenges. They can figure out how to open jars, boxes, or puzzles that contain food or other rewards. They can also learn from observation or experience how to escape from traps, nets, or tanks. Some octopuses have even been reported to display mischievous or playful behavior, such as squirting water at humans, playing with items, such as a plastic pill bottle that they repeatedly push into the stream of water circulating in their tank to watch it get shot out across the surface of the water in their tank and then retrieving it to start the process over again for ten times in a row in some cases for no other reason than they find it amusing. Octopuses can distinguish between different individuals, both of their own species and others. They can also recognize human caretakers based on their faces or clothing. Some octopuses have shown preferences or aversions toward certain humans, depending on how they were treated by them. They can also display different personalities and moods.

Perhaps the most impressive display of intelligence in octopuses is their ability to mimic other animals. Not only can they alter their appearance to blend with their surroundings, but they can also impersonate other creatures. The mimic octopus (Thaumoctopus mimicus) is a virtuoso in this regard, capable of imitating over 15 different species, such as highly poisonous sea snakes, lionfish, flatfish, and jellyfish. This mimicry serves to deter predators, lure prey, and confound competitors. Residing in the Indo-Pacific region, the mimic octopus faces numerous predators and competitors. Interestingly, the mimic octopus isn’t born with the ability to specifically mimic; it acquires this skill through observation and experimentation. It can also tailor its mimicry based on the situation and the observer. For instance, it might impersonate a sea snake when faced with a damselfish, known to be afraid of sea snakes, or a highly venomous lionfish when confronted with a large predator, or even a poisonous flatfish when traversing open sand, where it’s exposed to predators.

The mimic octopus naturally exhibits a light brown or beige color and shows a preference for river mouths and estuaries over reefs, which are typically favored by other octopus species for shelter and protection from predators. This habitat preference of the mimic octopus is attributed to its unique ability to mimic toxic animals, thereby reducing its risk of predation in open areas. The mimic octopus not only uses its mimicry defensively against predators, but also employs mimicry to approach cautious prey. For instance, it can imitate a crab’s potential mate, only to then consume the unsuspecting prey. The mimic octopus is not just intelligent, but also inventive and adaptable. It can even merge different mimics to create unique forms, like a half-sea snake and half-flatfish. This remarkable cognitive and behavioral complexity challenges our comprehension of animal intelligence. Scientists theorize that such behavior necessitates advanced cognitive abilities; it must comprehend how other animals perceive it and how it can manipulate their expectations by changing its appearance. Moreover, it must be capable of modifying its imitation strategy based on context; all demonstrations of advanced cognitive abilities. It has often been postulated that octopuses live a difficult life in environments dominated by vertebrate predators and that these evolutionary selective pressures crafted the highly intelligent, incredibly resourceful, and quite successful octopus species seen alive today. “Given all the remarkable capabilities that octopuses indeed have, I find it impossible that these extraordinary creatures are not conscious.”

Further Reading:

Baker, Beth (2010). "Unusual Adaptations: Evolution of the Mimic Octopus". BioScience. 60 (11): 962–962.

Peter Godfrey-Smith (2016). Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness. Farrar, Straus and Giroux.

Roger Hanlon, Michael Vecchione, Louise Allcock: (2018) Octopus, Squid & Cuttlefish: A Visual, Scientific Guide to the Oceans’ Most Advanced Invertebrates. The University of Chicago Press.

Harmon, Katherine (2013). "Mimic Octopus Makes Home on Great Barrier Reef". Scientific American.

"Mimic Octopuses". Marinebio.org. 2017.

John Roach (2001). "Newfound Octopus Impersonates Fish, Snakes". National Geographic.