Are aliens among us? Some marine biologists may be able to convince you that indeed there are. The precocious underwater group of marine creatures known as cephalopods sparks interest and intrigue in every marine field due to their unique and beautiful features. Cephalopods (which include the octopus, squid, cuttlefish, and nautilus) belong to the Mollusca phylum and possess a large head, bulbous eyes, and sprightly tentacles. The reason these animals seem so celestial to biologists comes from both the evolutionary history of the cephalopod and the baffling complex cognitive abilities that have resulted from their unique evolution. Who would have thought that an animal evolutionarily neighboring snails would be able to calculate an escape from an aquarium tank all the way back to their home in the ocean? (Bilefsky, 2016) Cephalopods present us with a brilliant opportunity to further advance our understanding of intelligence and cognition; examining comparative cognition with a focus on differences in nervous system structure between cephalopods and humans could yield a great deal of information on neural structure/function relationship and the connection to intelligence.
Cephalopod nervous systems are by far the largest out of all invertebrates and are significantly more complex than other animals in the Mollusca phylum (which includes snails and mussels). The typical cephalopod has a central nervous system with 80 million neurons and a peripheral nervous system made up of around 300 million neurons. The centralization of vertebrate nervous systems with a large brain and relatively simple neuronal organization in the periphery is not paralleled in cephalopods; there are individual “satellite brains” with an equivalent of a spinal cord for each individual tentacle. (Hanlon, 2019) There is an assumed connection with the structure of the cephalopod nervous system and the cognitive abilities they possess that is often compared to those of vertebrates.
Past neurobiological and marine research has demonstrated that cephalopods display complex behavioral patterns, leading researchers to hypothesize that these animals are capable of intricate cognitive abilities that arise from a well-developed nervous system. Observed behavioral patterns in cephalopods include emotional coloration, predatory camouflage, and advanced memory abilities. (Schnell et al., 2020) Underlying these patterns of behavioral flexibility may be mechanisms of complex cognition. Complex cognition is a common term in intelligence science and is described by specific cognitive abilities including causal reasoning, future planning, and mental attribution (an individual’s ability to recognize the thoughts and knowledge of others). (Schnell et al., 2020) These cognitive abilities are a signal of advanced, higher-order thinking that is usually only observed in vertebrates, rather than animals like snails and mussels. Against all odds, cephalopods produce highly intelligent behaviors that transcend common evolutionary reasoning.
The big question is, why did cephalopods evolve such a complicated nervous system and behavioral patterns when their closest evolutionary relatives have nothing similar? One theory is that with the loss of their hard, protective shell, an evolutionary need arose for these animals to colonize diverse environments and develop intricate behaviors for foraging and avoiding predators. (Schnell et al., 2020) For example, octopuses have been observed to use their specialized skin to mimic poisonous animals and deceive predators (Norman et al., 2001); this type of intelligent behavior requires the development of a complex nervous system.
Crash Course of Cephalopod Evolutionary Theory
loss of hard protective shell → colonization of diverse ecological niches → need to develop complex foraging/protective behaviors → evolution of complex cognition
Cephalopods are well-known for their camouflage and “shapeshift” skills during predatory signaling. Their perceptual capacities are often linked to their large brains and well-developed sense organs. (Schnell et al., 2020) These creatures have also been shown to display perception-based cognition in the form of object permanence, allowing them to keep track of objects when they are out of sight. (Sanders & Young, 1940) This capacity for out-of-sight tracking is an essential advantage for hunting; the cephalopod can identify the location of their prey even when they go into hiding. The understanding of object permanence in cephalopods has been used as evidence that these animals can perform mental attribution. (Call & Tomasello, 1999; Gruber et al., 2019) Mental attribution is an important cognitive function, as it indicates an animal’s proficiency in identifying others as separate but similar beings with consciousness of their own. This behavior should sound familiar, because it is! Mental attribution is an integral part of human cognition; we have the ability to discern what others are feeling, thinking, and perceiving. This is the primary reason why mental attribution is considered an important precursor to complex cognition.
Another example of complex cognition in cephalopods is their predisposition to rapid learning; all cephalopod groups (octopus, cuttlefish, squid) have shown a high capacity for associative and discrimination learning. (Schnell et al., 2020) Researchers have been able to teach cephalopods to inhibit predation through aversive associative learning as well as differentiate between specific visual features in exchange for a reward. (Boycott & Young, 1958) Cephalopods also have highly advanced spatial abilities and are efficiently able to find shelter in mazes through spatial cues. (Boal et al., 2000; Mather, 1991) While this vast range of learning modalities is impressive, it remains unknown whether these abilities are due to underlying complex cognitive mechanisms or simple associative mechanisms.
Cephalopods also display impressive memory skills through their well-developed memory recall. It has been observed that cuttlefish have episodic-like memory; there is behavioral evidence indicating that they remember exactly what they ate, where they ate it, and the time that has passed since. (Jozet-Alves et al., 2013) The presence of episodic-like memory in cuttlefish may indicate a capacity for future planning, as the animal will encode previous experiences to inform future behavior and decisions. Future planning is an attribute of complex cognition as it requires an animal to put together information and make decisions based on this previous knowledge.
A final idiosyncrasy which sets cephalopods apart is that of behavioral flexibility, defined as the ability of an individual to modify behaviour to respond effectively to new situations. This adaptation allows cephalopods to engage in highly efficient foraging, anti-predation methods, and communicative mating practices. (Schnell et al., 2020) Octopuses avoid visiting the same foraging areas that were depleted of resources from previous visits, suggesting that they update their memory flexibly to optimize their foraging behavior. (Forsythe & Hanlon, 1997) As an anti-predation strategy, both cuttlefish and squid can flexibly alter their body patterns in response to the threat of approaching predatory fish. This defense can be linked to the perceived mental state of predators which would then give further evidence for mental attribution in cephalopods. Veined octopuses have even been known to adorably use coconut shells as mobile dens as well as other protective materials as a tool for defense (Moynihan & Rodaniche, 1982; Hanlon & McManus, 2020). Cephalopods also use their rapid “shape-shifting” abilities to communicate for mating purposes. The male giant Australian cuttlefish, Sepia apama, produces multiple, successive displays in order to show increasing levels of threat. This dynamic level of communication creates flexible mating strategies further demonstrating complex and rapid decision-making behaviors (Schnell et al., 2016).
These myriad complex cognitive behaviors have led researchers to hypothesize higher levels of cognition specific to cephalopods that is increasingly interesting in both the fields of marine biology and comparative cognition, implicating neurobiology and its connection to cognitive science as a whole.
The current state of research on cephalopod intelligence and cognition is limited; very few studies truly quantify aspects of complex cognition in these animals. Anecdotal evidence, such as the viral video of an octopus opening a jar from the inside to escape, (Imgn Spaces, 2015) leaves us with little more than an interesting observation. However, knowing that these animals are capable of such complex behavior allows us to form specific, testable questions to further investigate the mechanisms behind this display.
There are a few recent examples of studies that scientifically examine behavioral flexibility to provide evidence for the complex cognition hypothesis in cephalopods. In 2020, evidence was found that cuttlefish are capable of displaying flexible predatory behavior where they change strategies depending on the availability of preferred food. (Billard et al., 2020) The experiments show that cuttlefish are able to learn food availability and make decisions for future consumption based on this encoded knowledge. This experiment also gives evidence that cuttlefish have executive control; they can refrain from eating less preferable food when they know that more desirable food will be available later. More research is needed to definitively determine that cuttlefish can plan for the future; this study does not determine if they act independently of their current motivational state, but it does give strong evidence in favor of this theory. This is one of only a handful of studies that quantitatively assess complex cognition in cephalopods; more research and applications of the scientific method are necessary before reaching conclusions about the intelligence these creatures possess. We must rule out Occam’s razor and find evidence against the theory that these behaviors arise from simple associative learning before concluding that cephalopods’ behavioral flexibility is due to complex cognitive mechanisms. (Schnell et al., 2020)
Now, we’ve discussed camouflage, shapeshifting learning, planning, memory, behavioral flexibility, and that is all good and exciting; there’s no doubt that cephalopods are smart and cool. But why should we care at all? Aside from the intriguing fact that these species among us are so complex and odd that one might even consider them alien, this type of comparative cognition opens up further context to cognitive science to help understand the basis for complex cognition. In recent years, cognitive scientists have found that the reality of human cognition goes beyond the traditional framework of “structure determines function”. This issue has slowed down our ability to understand intelligence and how it arises, but with more research in these kinds of complex cognition in a variety of different nervous system structures and in vastly different kinds of organisms, we may be able to draw newer connections between structure and function. This added perspective of cephalopod cognition may not give us all of the answers to cognition, but with further understanding of vastly different structures connected to similar functions, we can begin to form better conclusions around the mysteries of cognition. With this kind of understanding, we will eventually be able to create new and better AI models and push the field of neurotechnology further than we could have before; all thanks to a mollusk whose head got way too big.
This article was written by Mridula Vardhan and Annabel Teagan, and was edited by Jandy Le. Mridula is a fourth-year UC Berkeley student studying Molecular and Cellular Biology with an emphasis in Neurobiology. Annabel is a third-year UC Berkeley student studying Cognitive Science. Jandy is a third-year UC Berkeley student studying Integrative Biology. Vien Yen Ho Pham produced the graphic. She is a second-year student at UC Berkeley studying Molecular and Cellular Biology with an emphasis in Neurobiology.