Continuum frameworks predict something the modern scientific worldview (MSW) disregards: interiority should be widespread rather than rare. If interiority differentiates from an undivided ground rather than emerging from matter, we should expect to find it manifesting across diverse architectures wherever sufficient neural complexity exists. The MSW framework, by contrast, treats consciousness, We generally use “interiority” for the experiential dimension to maintain philosophical precision, though we occasionally use “consciousness” colloquially or when discussing how others frame these questions. particularly human-like consciousness, as an anomalous late arrival—something that appears only under very specific and rare conditions: centralized neural integration, particularly the mammalian neocortex or structures closely approximating it. By this logic, interiority should be largely confined to larger-brained mammals, and appearing only recently in evolutionary time.
This difference in predictions creates an empirical test. What do we actually find when we look across the tree of life? The answer depends critically on what we’re looking for and what counts as evidence. As we’ll see, the very criteria we use to assess interiority in other species encode assumptions about what interiority is and where it comes from. The MSW naturally gravitates toward anthropocentric markers—language, tool use, self-recognition—criteria that make human consciousness the measuring stick. Continuum frameworks, by contrast, suggest we should expect interiority to manifest through whatever organizational structures evolution has provided, looking less like human experience and more like something suited to each species’ particular way of engaging with reality.
Before examining specific cases, we need to understand why the framework or lens we view evidence through determines or shapes what we can see. The same behavioral observations that look like mere mechanism through one lens can appear as manifestations of rich inner life through another. This isn’t a matter of being more or less rigorous—it’s about recognizing that the evidence doesn’t force a single interpretation. Different frameworks make different patterns visible.
Human Perceptual Frameworks
Consider the classic perceptual illusions: Rubin’s vase that flips between two faces and a vessel, or the Necker cube that reverses depth spontaneously. These demonstrate something fundamental about perception—we don’t passively receive reality, we actively construct it. The sensory data remains constant, but our perceptual system organizes it into (sometimes different) coherent wholes. What we “see” depends not just on what’s there, but on how our visual system structures the input.
This reveals a deeper principle about perception that philosophers call the rejection of naive realism: the recognition that what we experience as “direct” perception is actually the result of sophisticated constructive processes. We don’t have unmediated access to reality—we have access to our brain’s model of reality, constructed from fragmentary sensory data by organizational principles built into our neural architecture. The table in front of you feels solid and immediate, but what you’re experiencing is your brain’s inference about the patterns of photons hitting your retina. Your belief that you are directly experiencing reality is itself a construction.
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Species-Specific Realities
Harry Jerison, the pioneering neurobiologist, made a crucial observation: brains evolved not to represent reality as it “really is,” but to construct species-characteristic experiential realities suited to particular ecological niches. A bat’s echolocation doesn’t give it inferior access to the same reality we perceive visually—it constructs a characteristically bat-like experiential world, organized around acoustic information in ways we can barely imagine. Thomas Nagel’s famous essay “What Is It Like to Be a Bat?” wasn’t asking whether bats have consciousness, but highlighting that even if they do, their experiential reality almost certainly is so different from ours that we cannot reconstruct it from a human perspective.
The evidence for species-specific reality construction is everywhere. Mantis shrimp possess sixteen types of photoreceptor cells compared to our three—their color space is literally more dimensional than ours. Bloodhounds construct their experiential world primarily through olfaction, detecting scent concentrations we cannot fathom, tracking temporal gradients in odor that create a kind of olfactory time-travel. Elephants communicate through infrasonic rumbles traveling kilometers through the ground, their social world structured by acoustic channels invisible to us. Cetaceans navigate and socialize in three-dimensional acoustic space, using sophisticated sonar to perceive internal structures of objects and possibly internal states of other animals.
The crucial point: there is no privileged vantage point, no species-neutral perspective from which to assess whose reality is more “real.” Each species constructs the experiential reality its nervous system is organized to produce, suited to its particular way of engaging with the world. Our reality isn’t the reality—it’s the reality constructed by human perceptual and cognitive systems.
This has profound implications for assessing consciousness in other species: we cannot assume that human-like experience is the gold standard against which all other forms of consciousness should be measured.
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Intellectual Frameworks
The same principle applies to theoretical frameworks. The MSW and continuum frameworks aren’t just different opinions about consciousness—they’re different organizational structures that make different patterns visible, much like perceptual frameworks making different aspects of the same sensory data salient.
Through the MSW lens, we see: physical processes → neural complexity → (mysterious emergence) → consciousness. This framework naturally directs attention toward mechanisms, computational properties, information processing. Consciousness appears as something that needs to be explained, generated, produced from non-conscious components. The explanatory burden falls on showing how mechanism can give rise to experience.
Through the continuum lens, we see: undifferentiated ground → organizational differentiation → consciousness and physicality as complementary aspects. This framework naturally directs attention toward manifestation, integration, the expression of inherent potential through organizational structure. Consciousness appears as something that becomes articulated rather than produced, differentiated rather than emerged. The explanatory burden falls on showing how organizational principles shape and structure what was always present in potential.
These aren’t neutral “theories” we can step outside of to evaluate objectively—they’re the frameworks through which evaluation itself occurs. Like Jerison’s species-specific realities, they construct characteristically different intellectual worlds, making different questions natural and different evidence salient.
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Implication for Assessing Other Minds
When we assess evidence for interiority in other species, our framework shapes what we look for and how we interpret what we find. If we think that consciousness emerges from computational complexity, we naturally ask: “Do they have enough neurons? The right kind of processing? Human-like cognitive capabilities?” On the other hand, if we think that interiority differentiates through organizational structure, we ask different questions: “What kind of experiential reality does their neural architecture construct? How does their particular organization shape their engagement with the world?”
The wrong question—encouraged by anthropocentric bias within the MSW—is: “Do they possess human-like characteristics?” This treats human consciousness as the measuring stick, other species as deficient versions.
The right question—natural within continuum frameworks—is: “How richly do they experience reality given their particular organizational structure?” This allows for the possibility that sophisticated interiority might manifest through organizational principles radically different from our own.
Continuum frameworks predict not a binary (conscious/non-conscious) but a spectrum—degrees of richness, integration, temporal depth, affective range, each shaped by particular organizational solutions to the problem of being a living, embodied creature engaging with a complex world.
What We’re Looking For
To assess consciousness across species, we need a minimal working definition that doesn’t build in anthropocentric assumptions. Thomas Nagel’s formulation remains the most useful: consciousness exists where “there is something it is like” to be that creature—some experiential quality, however simple or complex, however similar or different from human experience.
A note on terminology: We’ll use several terms somewhat interchangeably - ‘consciousness,’ ‘interiority,’ ’experience,’ ‘inner life,’ ’experiential quality.’ Each term carries anthropocentric baggage, since we can only describe other forms of consciousness through human conceptual apparatus. We typically use ‘interiority’ instead of ‘consciousness’ in our arguments as ‘interiority’ is more precise, but also use ‘consciousness’ in instances of its original use.
The minimal definition of interiority aligns with continuum frameworks. This is not a question of whether the light switch of interiority is on or off, but rather how richly integrated and articulated a creature’s experiential reality might be. The continuum framework suggests consciousness varies along multiple dimensions: temporal depth (how extended in time is experience?), affective range (how varied and nuanced are felt states?), integration (how unified is the experiential field?), and differentiation (how articulated are distinctions within experience?).
How do we recognize consciousness in beings we can’t communicate with directly? We look for patterns that suggest rich inner experience rather than mere mechanical response.
Some behaviors point to genuine thinking and learning. Can an animal solve new problems it hasn’t encountered before? Does it learn from experience and change its approach? Can it navigate complex situations flexibly rather than following rigid instincts? These capacities suggest a mind actively engaging with the world, not just running pre-programmed responses.
Other evidence comes from how animals seem to feel about things. Do they show clear preferences—approaching what they like, avoiding what they dislike? Do they form lasting bonds with others? Do they play when there’s no survival benefit, just for the apparent pleasure of it? These patterns suggest experiences that matter to the animal itself—states that feel good or bad, not just neutral information processing. . Brain structure provides supporting evidence. Large, highly-connected brains with specialized regions for memory, emotion, and social processing create the physical foundation for rich mental life. While we can’t prove consciousness from brain anatomy alone—that remains philosophically mysterious—neural architecture combined with behavior and apparent feeling appears to have greater explanatory power.
When evidence converges—sophisticated behavior, apparent feelings, and neural complexity all pointing in the same direction—we have reasonable grounds for inferring rich conscious experience. The inference remains indirect, as it must be for any consciousness other than our own. But this is the nature of understanding other minds: we work with the best available evidence and remain appropriately humble about certainty.
One crucial point before examining specific cases: the evidence we’ll review doesn’t force a single interpretation. It’s compatible with various frameworks—emergence, panpsychism, continuum views. What continuum frameworks provide isn’t proof but better fit: they make widespread consciousness across diverse species naturally intelligible rather than puzzling. They predict what we actually find rather than requiring ad hoc explanations for why consciousness appears in evolutionarily distant lineages with radically different brains.
With this framework made explicit, we can examine what the evidence actually shows.
Octopuses
Among invertebrates, octopuses present the most compelling case for sophisticated consciousness—and the most alien architecture for manifesting it.
Octopuses possess roughly 500 million neurons, comparable to dogs, but distributed radically differently. Godfrey-Smith, P. (2016). Other Minds: The Octopus, the Sea, and the Deep Origins of Consciousness. Farrar, Straus and Giroux. Two-thirds of these neurons reside in their eight arms, not their central brain. Each arm operates with substantial autonomy—able to explore, grasp, and even taste independently while the brain attends to other tasks. Zullo, L., & Hochner, B. (2011). “A new perspective on the organization of an invertebrate brain.” Communicative & Integrative Biology, 4(1), 26–29. This isn’t peripheral processing feeding information to a central controller. It’s genuinely distributed cognition, where mind emerges from coordination of semi-independent subsystems rather than centralized command. This architecture challenges assumptions embedded deep in neuroscience and philosophy of mind—that consciousness requires centralization, a unified processing hub integrating disparate inputs into coherent experience. The octopus suggests otherwise.
Their evolutionary history makes the case more striking. Cephalopods diverged from our lineage more than 500 million years ago, before the Cambrian explosion produced most modern animal body plans. Their sophisticated cognition evolved entirely independently, through half a billion years of mollusk neural evolution along a pathway sharing no recent common ancestors with vertebrates. They possess no neocortex, no corpus callosum, no hippocampus—none of the structures typically associated with complex cognition in mammals. Yet convergent behavioral evidence suggests substantial experiential depth.
The behavioral indicators are remarkable. Octopuses are prolific problem-solvers, learning to unscrew jars to access food inside—sometimes within just a few trials. Fiorito, G., & Scotto, P. (1992). “Observational learning in Octopus vulgaris.” Science, 256(5056), 545–547. They navigate mazes, solve detour tasks, and learn to pull levers for rewards. These aren’t simple conditioned responses; octopuses often explore novel setups, attempt different strategies, and display what can only be described as exploratory learning. More controversially, some evidence suggests observational learning—octopuses learning to open jars faster after watching a conspecific perform the task. Ibid. Fiorito & Scotto (1992). While replication has been inconsistent, the finding would be notable given that octopuses are largely solitary animals without complex social structures.
Tool use—rare in the animal kingdom, rarer still among invertebrates—has been documented in multiple species. The veined octopus (Amphioctopus marginatus) carries halved coconut shells across the sea floor, sometimes awkwardly clutching them under their bodies, then reassembles the halves and hides inside. This is widely considered true tool use: collecting, transporting, and assembling non-food objects for future benefit. Finn, J. K., Tregenza, T., & Norman, M. D. (2009). “Defensive tool use in a coconut-carrying octopus.” Current Biology, 19(23), R1069–R1070. Other octopuses stack shells to block den entrances, use jets of water to move objects or clean shelters, collect bottle caps and coral fragments for environmental manipulation. Each arm’s precision and fine motor control—supported by its own neural network—enables delicate manipulation that can orient and pass objects from arm to arm, aligning them for insertion or deployment.
Perhaps the most striking manifestation of this distributed interiority is their skin. Octopuses can change color, pattern, and texture in milliseconds to match their surroundings with photographic precision. This display is not purely a centrally-controlled output. Research reveals that octopus skin contains opsins—the same light-sensitive proteins found in eyes—suggesting the skin itself may “see” and respond to local light conditions. Ramirez, M. D., & Oakley, T. H. (2015). “Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides.” Journal of Experimental Biology, 218(10), 1513-1520. The animal doesn’t just observe the world from a distance; its entire surface participates in perception and expression, dissolving the boundary between internal state and external appearance.
The affective dimension suggests valenced experience. Captive octopuses given floating pill bottles repeatedly pushed the bottles into water jets, watched them float away, then retrieved and repositioned them to repeat the cycle. These interactions weren’t linked to feeding or escape and persisted over multiple sessions—interpreted as object play without obvious functional purpose. Kuba, M. J., Byrne, R. A., Meisel, D. V., & Mather, J. A. (2006). “When do octopuses play? Effects of repeated testing, object type, age, and food deprivation on object play in Octopus vulgaris.” Journal of Comparative Psychology, 120(3), 184–190. Octopuses actively seek novelty, preferring new objects to familiar ones, approaching and manipulating unfamiliar stimuli including researchers’ equipment and cameras. Mather, J. A., & Anderson, R. C. (1999). “Exploration, play, and habituation in octopuses (Octopus dofleini).” Journal of Comparative Psychology, 113(3), 333–338. They display individual personalities, form preferences, show what appears to be curiosity-driven behavior—suggesting internally motivated engagement with their environment, not merely reactive responses.
Memory systems are sophisticated. Octopuses navigate complex mazes, showing learning curves and error correction, retaining maze solutions over hours or days. Mather, J. A. (1991). “Navigation by spatial memory and use of visual landmarks in octopuses.” Journal of Comparative Physiology A, 168(4), 491–497. They use visual landmarks to guide behavior, recognize individual humans, and adjust hunting strategies based on past experience. This demonstrates spatial working memory and environmental mapping—advanced forms of mental representation once thought exclusive to vertebrates.
The neural organization supporting these capacities differs fundamentally from vertebrate brain plans, yet achieves comparable sophistication through different means. The distributed processing system, with its 500 million neurons organized into semi-autonomous subsystems, shows that sophisticated cognition doesn’t require the centralized architecture we see in mammals. Specialized structures for integration exist, but organized along different principles, with different connectivity patterns, producing different solutions to the problem of coordinated behavior.
What this means for continuum frameworks is clear. More than 500 million years ago, the mollusk lineage began evolving neural systems entirely independently from vertebrates. That pathway led to beings capable of tool manufacture, play, individual personality, flexible problem-solving, and apparent curiosity—all accomplished through radically different organization. Consciousness manifests through whatever architecture provides sufficient integration and complexity. It doesn’t require our brain plan, our neural structures, our centralized processing. The octopus demonstrates that different organizational principles can support rich experiential depth. Not requiring vertebrate brains or mammalian cortex, consciousness found another way—a distributed, embodied intelligence emerging from arms that think and a body that perceives.
Corvids: Intelligence Without Mammalian Architecture
Crows, ravens, jays, and magpies—the corvid family—present perhaps the most philosophically significant challenge to assumptions about what consciousness requires. They show cognitive sophistication rivaling great apes, yet they accomplish this through a fundamentally different neural architecture. Emery, N. J., & Clayton, N. S. (2004). “The mentality of crows: Convergent evolution of intelligence in corvids and apes.” Science, 306(5703), 1903-1907. Where mammals evolved large, elaborated neocortices, birds took a different path. Corvids possess no neocortex at all. Instead, they developed a densely packed structure called the pallium, organized along completely different principles yet producing remarkably similar outcomes.
This is convergent evolution in its purest form. The last common ancestor of birds and mammals lived roughly 320 million years ago—a small reptile-like creature with minimal brain elaboration. From that shared starting point, mammalian and avian lineages independently evolved sophisticated cognition through radically different neural implementations. That both pathways succeeded demonstrates something crucial: consciousness doesn’t require our specific architecture. Different organizations can support comparable complexity.
The behavioral evidence is striking. New Caledonian crows (Corvus moneduloides) are the only nonhuman species known to craft compound tools in the wild, shaping hook-like implements from leaves or wire to extract food. Hunt, G. R., & Gray, R. D. (2004). “The crafting of hook tools by wild New Caledonian crows.” Proceedings of the Royal Society B, 271, S88-S90. This isn’t merely using found objects but manufacturing them to specification, selecting materials based on functional properties, even improving designs through individual innovation. In laboratory tests, they solve multi-step puzzles requiring insight and causal reasoning, not just trial-and-error learning. Betty, a famous New Caledonian crow studied in Oxford, spontaneously bent wire into a hook to retrieve food from a tube—a task she had never encountered, requiring insight into materials, mechanics, and desired outcome. Taylor, A. H., et al. (2007). “Spontaneous metatool use by New Caledonian crows.” Current Biology, 17(17), 1504-1507.
Western scrub-jays demonstrate future planning, selecting and saving tools they’ll need for tasks tomorrow while suppressing the temptation to use those tools for immediate rewards. Raby, C. R., et al. (2007). “Planning for the future by western scrub-jays.” Nature, 445(7130), 919-921. They cache food in places where they have previously experienced hunger and can differentiate between perishable and non-perishable items, adjusting their caching behavior accordingly. This requires mentally representing future states, evaluating current options against anticipated needs, and exercising self-control—cognitive capacities associated with prefrontal cortex in mammals. Yet these birds accomplish this without prefrontal cortex, using their pallial structures instead.
Corvids show sophisticated social cognition. Scrub jays cache food, but if they’re watched by other jays while caching, they later move those caches when alone—suggesting they understand that others have visual perspectives and intentions. Dally, J. M., Emery, N. J., & Clayton, N. S. (2006). “Food-caching western scrub-jays keep track of who was watching when.” Science, 312(5780), 1662-1665. Birds who have themselves stolen from caches are more likely to re-cache their own food when watched, suggesting they attribute to others the thieving intentions they themselves have experienced. Emery, N. J., & Clayton, N. S. (2001). “Effects of experience and social context on prospective caching strategies by scrub jays.” Nature, 414(6862), 443-446. Ravens engage in complex social maneuvering, forming alliances, tracking relationships, even appearing to deceive competitors.
The affective dimension appears equally rich. Corvids play—sliding down snowy roofs repeatedly, dropping and catching objects in flight, engaging with materials for no apparent functional purpose. Pellis, S. M., & Iwaniuk, A. N. (2000). “Adult-adult play in primates: Comparative analyses of its origin, distribution and evolution.” Ethology, 106(12), 1083-1104. They form long-term pair bonds, showing apparent distress at partner loss. American crows (Corvus brachyrhynchos) exhibit group gatherings around deceased individuals—“crow funerals”—during which they call loudly and may avoid the area in the future, behavior that parallels elephant and cetacean responses to death. Swift, K. N., & Marzluff, J. M. (2015). “Wild American crows gather around their dead to learn about danger.” Animal Behaviour, 109, 187-197.
Parrots represent another avian lineage demonstrating sophisticated cognition through radically different architecture. African grey parrots, particularly Alex—trained by Irene Pepperberg over three decades—demonstrated symbolic communication, abstract categorization, and numerical cognition typically associated only with great apes. 18 Irene M. Pepperberg, The Alex Studies: Cognitive and Communicative Abilities of Grey Parrots (Harvard University Press, 1999). Alex learned over 100 vocal labels, answered questions about color, shape, and quantity, and understood concepts like “same,” “different,” and absence. His responses met criteria for symbolic reference: arbitrary labels, semantic meaning, productivity in novel contexts. 19 Irene M. Pepperberg, “Grey parrot numerical competence: a review,” Animal Cognition 9 (2006). Like elephants and cetaceans, parrots demonstrate vocal learning—the capacity to acquire new vocalizations through imitation—found in only a handful of lineages. 20 Timothy F. Wright, “Regional dialects in the contact call of a parrot,” Proceedings of the Royal Society B: Biological Sciences 263 (1996). (This establishes the vocal learning/dialect capacity). Kea parrots show problem-solving abilities rivaling corvids in multi-step mechanical tasks. 21 Alice M. I. Auersperg et al., “Flexibility in problem solving and tool use of kea and New Caledonian crows,” PLoS ONE 6 (2011). That both corvids and parrots, evolving independently within Aves, demonstrate such cognitive sophistication strengthens the inference that avian pallium organization—despite lacking mammalian cortical layering—provides architecture for rich conscious experience.
The neural architecture supporting these capacities differs fundamentally from mammalian organization. Corvid brains are small—a crow’s brain weighs perhaps 15 grams compared to 1,400 for humans. But they achieve high neuron density through different packing strategies. Neuroscientist Suzana Herculano-Houzel demonstrated that corvids possess roughly the same number of forebrain neurons as monkeys, despite having brains only a quarter of the mass. 22 Seweryn Olkowicz, Suzana Herculano-Houzel, et al., “Birds have primate-like numbers of neurons in the forebrain,” Proceedings of the National Academy of Sciences 113, no. 26 (2016). This is the landmark study showing that avian brains have much higher neuronal densities than mammalian brains, allowing small bird brains to hold as many information-processing neurons as much larger primate brains. The avian pallium lacks the layered cortical structure of mammals but contains massive processing power in a compact package. Their brain-to-body size ratios are among the highest of all birds, comparable to those of chimpanzees. The connectivity patterns differ, the functional organization differs, yet the computational power appears comparable for many tasks. Even mirror self-recognition—once thought to require mammalian cortex—has been demonstrated in magpies (Pica pica), suggesting bodily self-awareness despite lacking a neocortex. Prior, H., Schwarz, A., & Güntürkün, O. (2008). “Mirror-induced behavior in the magpie (Pica pica): Evidence of self-recognition.” PLoS Biology, 6(8), e202.
What this demonstrates for continuum frameworks is profound. Consciousness doesn’t emerge only through mammalian neocortex. It manifests through whatever organization provides sufficient integration, flexibility, and complexity. The avian solution differs from the mammalian solution, evolved independently over 320 million years, yet both work. This makes the prediction that cetacean brains—organized along yet different principles—might also support rich consciousness less surprising, more natural. Evolution has found multiple solutions to the problem of sophisticated cognition. The continuum framework predicts exactly this: consciousness manifesting through diverse organizations, each suited to its lineage’s evolutionary history and ecological pressures.
Great Apes: Our Closest Relatives and the Continuity Question
Great apes—chimpanzees, bonobos, orangutans, and gorillas—share 97-99% of their DNA with humans, making them our closest living relatives. Finch & Stanford (2004) - DNA similarity This phylogenetic proximity raises a crucial question for consciousness studies: if humans possess rich inner lives, where in our shared evolutionary history did consciousness supposedly “emerge”? The continuum framework suggests no such emergence occurred—rather, the sophisticated consciousness we observe in great apes represents variation in degree rather than kind, differing organizational expressions of the same fundamental capacity.
Gordon Gallup’s classic mirror self-recognition experiments demonstrated that chimpanzees, after being anesthetized and marked with dye on their faces, touched the marks upon seeing their reflection—indicating recognition of the image as self rather than other. Gallup (1970) - MSR in chimpanzees Orangutans reliably pass the test; gorillas less consistently. Beyond mirrors, chimpanzees demonstrate bodily self-awareness in tasks where their own body becomes an obstacle, and engage in tactical deception that suggests awareness of themselves as agents whose actions can be hidden from others. Byrne & Whiten (1992) - Tactical deception
Theory of mind capacities appear across multiple domains. Subordinate chimpanzees preferentially steal food that dominant individuals cannot see, demonstrating sensitivity to what others perceive and likely know. Hare, Call, & Tomasello (2001) - Visual perspective-taking In a landmark study, Krupenye and colleagues used looking-time measures to show that great apes anticipate actions based on another individual’s false belief—an ability long considered uniquely human. Krupenye et al. (2016) - False-belief understanding While some researchers argue these behaviors might reflect sophisticated behavior-reading rather than genuine mental-state attribution, the weight of converging evidence suggests apes model others’ perspectives.
The affective dimension is equally compelling. Frans de Waal documented systematic post-conflict reconciliation and third-party consolation—behaviors interpreted as proto-empathy or precursors to moral emotion. de Waal & van Roosmalen (1979) - Reconciliation and consolation Apes show sensitivity to fairness in inequity aversion experiments, protesting unequal treatment. Mother apes carry deceased infants for extended periods; groups engage in what appears to be mourning behavior around recently deceased members. Biro et al. (2010) - Mothers carrying dead infants These responses suggest emotional processing extending beyond immediate reaction to sustained affective engagement with death and loss.
Cultural transmission appears in tool use and social customs. Andrew Whiten and colleagues identified 39 behavior patterns—including specific tool-use techniques and grooming traditions—that vary culturally among chimpanzee communities rather than tracking genetic or environmental differences. Whiten et al. (1999) - Cultural variation in chimpanzee communities Wild chimpanzees use termite-fishing probes, leaf sponges, stone hammers and anvils, even sharpened sticks for hunting. Orangutans fashion leaves into gloves and napkins, construct elaborate sleeping platforms, improvise tools for seed extraction. These traditions transmit socially across generations.
Planning and future orientation appear in multiple contexts. Apes select and transport tools for later use, resisting more immediate rewards. Mulcahy & Call (2006) - Tool saving Wild chimpanzees track fruiting schedules and plan travel routes based on past experience and expected future availability, suggesting temporal depth to their decision-making.
Communication studies reveal both symbolic and gestural sophistication. Washoe learned American Sign Language; Kanzi, a bonobo, comprehended spoken English and used lexigrams to communicate desires. Savage-Rumbaugh & Lewin (1994) - Kanzi Wild apes employ rich gestural repertoires, persisting or changing signals when recipients fail to respond, choosing gestures based on audience attention—evidence of goal-directed, intentional communication. Hobaiter & Byrne (2011) - Gestural repertoires
What great apes demonstrate for continuum frameworks is evolutionary continuity rather than human exceptionalism. The capacities we observe—self-awareness, empathy, culture, planning, symbolic thought—don’t emerge suddenly in humans but represent elaborations of capacities present in our closest relatives. That these capacities appear without human-like language challenges language-centric views of consciousness. That they appear in species sharing recent common ancestry suggests consciousness as fundamental inheritance rather than recent evolutionary innovation.
Plants: Testing the Boundaries
Plants present a crucial test case for any framework claiming consciousness manifests across diverse organizations. They demonstrate sophisticated information processing, flexible behavior, and distributed signaling networks—all without centralized nervous systems. Do they possess “something it is like” to be them? Or do they represent exquisite responsiveness without experiential quality? The question exposes assumptions about what organizational features consciousness requires.
The evidence for plant sophistication has accumulated dramatically over recent decades. When plants are attacked or stressed, they emit volatile organic compounds that neighboring plants detect and respond to by upregulating defensive chemistry. Baldwin et al. (2006) - Volatile signaling overview Damaged sagebrush induces resistance in neighboring tobacco plants; willows and poplars increase chemical defenses when exposed to volatiles from insect-damaged conspecifics. Karban et al. (2006) - Sagebrush-tobacco communication This “talking trees” phenomenon appears across diverse species and contexts, though debate persists whether this constitutes genuine communication or merely chemical signaling that other plants happen to detect.
Underground, the complexity deepens. Mycorrhizal fungi connect plant roots into expansive networks through which resources and signals move. Susan Simard’s research demonstrates carbon transfer between different tree species, warning signals traveling through fungal networks to induce defenses in neighbors under aphid attack, even water transfer through hyphal connections between drought-stressed and well-watered individuals. Simard et al. (1997); Babikova et al. (2013); Song et al. (2015) - Mycorrhizal networks Recent critical reviews caution against over-interpreting these networks anthropomorphically, but the basic phenomenon—distributed information exchange shaping community-level responses—remains well-established. Karst et al. (2023) - Critical review of wood-wide web
Plants also demonstrate forms of memory. When Mimosa pudica plants were repeatedly dropped onto soft surfaces, they eventually stopped closing their leaves in response—but still responded to novel stimuli, demonstrating genuine habituation rather than mere fatigue, with the response suppression persisting for weeks. Gagliano et al. (2014) - Mimosa habituation Plants show long-lasting “immune memories,” responding more strongly to pathogens or herbivores after prior exposure—biochemical priming that enhances future defense. Conrath et al. (2006); Hilker & Schmülling (2019) - Plant immune memory Claims for associative learning remain controversial; Gagliano and colleagues reported Pavlovian conditioning in pea plants, but more controlled replications found no evidence of such learning. Gagliano et al. (2016); Markel (2020) - Associative learning controversy
Electrical signaling adds another dimension. Plants generate action potentials that propagate across tissues in response to wounding, salinity, light changes, or mechanical stimulation. Fromm & Lautner (2007) - Electrical signals in plants Venus flytraps demonstrate particularly striking electrical sophistication: they “count” prey touches using action potentials, requiring two stimulations within twenty seconds before expending the energy to close their traps—a form of integration suggesting rudimentary computation. Böhm et al. (2016) - Venus flytrap counting Long-distance signaling mediated by glutamate and calcium waves allows rapid communication across plant bodies, functionally analogous to though mechanistically distinct from animal nervous systems.
Social behavior appears in unexpected forms. Plants recognize kin versus non-kin through root-secreted chemicals, reducing competitive root foraging among siblings while maintaining it with unrelated neighbors. Dudley & File (2007) - Kin recognition They adjust root placement flexibly based on nutrient patches, neighbor identity, and mechanical obstacles—some species showing active avoidance of competing roots or preferential overlap with kin. Cahill et al. (2010); Gruntman & Novoplansky (2011) - Root behavior These behaviors parallel, albeit at vastly different timescales, the context-dependent problem-solving found in animal foraging.
The design problem becomes acute: Can such sophisticated, flexible, context-dependent behavior occur through purely biochemical mechanisms without any experiential component? The mechanistic explanation is available—electrical and chemical signaling, genetic regulatory networks, cellular-level responses to environmental gradients. Nothing in plant behavior definitively requires invoking subjective experience. Yet the apparent purposiveness, the integration of information across scales, the flexible responsiveness to novel situations, all have the functional character we associate with agency.
The crucial difference may lie in integration architecture. Animal nervous systems create centralized points where diverse information streams converge, where past and present integrate, where unified responses emerge from distributed inputs. Plants lack such centralization—their processing remains fundamentally distributed, with no clear locus of integration, no “place” where information comes together to create a unified experiential field. The Venus flytrap counts touches, but is there anywhere in the plant where this counting is experienced rather than merely implemented through electrical state changes in trigger hairs?
This distinction—between distributed information processing and centralized experiential integration—may mark a genuine boundary for consciousness. The psychophysical continuum framework predicts consciousness manifests where organizational structure supports integrated, unified experience. It needn’t predict consciousness in every responsive system, only that consciousness becomes more articulated as organization becomes more integrated and differentiated. Plants may represent sophisticated responsiveness—genuine information processing, flexible behavior, even primitive forms of learning—without crossing the threshold into subjective experience.
Yet honest uncertainty persists. If consciousness differentiates from an undivided ground rather than emerging from matter, who can definitively say where that differentiation begins? The framework resists hard boundaries, suggesting instead that the question “are plants conscious?” may be asking for artificial precision about a genuinely graded phenomenon. Perhaps the better question is: What degree and kind of experiential articulation, if any, do different levels of organizational integration support?
Plants thus test the framework without breaking it. They demonstrate that sophisticated behavior need not require consciousness, that distributed information processing can produce flexible responses without centralized experience. Yet they also show that life itself involves forms of sensitivity, responsiveness, and information integration that resist purely mechanistic description. They occupy a conceptual space between obvious non-consciousness (rocks) and obvious consciousness (mammals), making the reality of gradation visible while reminding us that gradation need not mean everything grades smoothly into everything else.
Marine Mammals: A Second Evolutionary Peak
Two peaks thus emerge from this evolutionary survey: terrestrial and marine. The terrestrial peak, exemplified by elephants and great apes, demonstrates sophisticated consciousness through mammalian neocortical architecture. But evolution has conducted a parallel experiment in an utterly alien medium.
The odontocetes—toothed whales including dolphins, orcas, and sperm whales—independently evolved multiple hallmark traits of human- and ape-like cognition through an entirely separate evolutionary pathway in the ocean. They possess enormous cortical neuron counts: pilot whales have over 37 billion neurons, more than twice the human count. Orcas have brains weighing five kilograms, sperm whales nine kilograms—the largest brains in Earth’s history. These lineages achieved high encephalization millions of years ago and maintained it with remarkable stability.
Beyond sheer neural scale, cetaceans demonstrate complex cultures with learned traditions transmitted across generations, coalition politics involving multi-level strategic alliances, sophisticated symbolic communication through group-specific dialects, and mirror self-recognition indicating self-awareness. They share with elephants and great apes the specialized von Economo neurons associated with social-emotional processing. That multiple phylogenetically distant lineages independently converged on this suite of traits suggests sophisticated consciousness requires certain organizational features, whether manifesting in terrestrial or marine architectures.
Understanding what these convergences reveal about consciousness requires examining how brains relate to conscious experience generally—questions of encephalization, neural organization, and why different architectures can support comparable experiential depth. The next chapter develops these principles before turning to the cetacean case specifically, while Chapter 6 explores the behavioral sophistication these brains support. For now, the pattern suffices: consciousness manifests through diverse organizations across radically different environments, supporting continuum frameworks’s prediction.
Citations needed (cetaceans):
- Neuron counts: (sources for pilot whale 37B)
- Brain masses: (standard cetacean neuroanatomy sources)
- Encephalization timeline: (evolutionary studies)
- Cultural transmission: Fox et al. 2017, Connor et al. 1998
- Coalition politics: Connor et al. 2022
- Mirror self-recognition: Reiss & Marino 2001
- VENs: Hakeem et al. 2009
Limitations and Uncertainties
The evidence surveyed here supports the prediction of continuum frameworks that consciousness manifests widely across diverse neural organizations. But honest inquiry requires acknowledging what this evidence cannot establish and where genuine uncertainty remains.
Most fundamentally, we cannot move from complex behavior to rich experience through pure logic or observation. When we interpret elephant mourning, corvid problem-solving, or octopus tool use as manifestations of conscious engagement, we are making a framework choice rather than an empirical deduction. The continuum treats consciousness as fundamental, leading us to interpret sophisticated behavior as experiential integration expressing itself through action. But other frameworks could theoretically account for the same phenomena—sophisticated information processing without accompanying experience, sometimes termed “philosophical zombies.” While we find this vanishingly unlikely given evolutionary considerations and the continuum’s coherence, alternative interpretations remain logically possible, even if pragmatically implausible.
The inference problem cuts deeper still. We observe behavior, never experience directly. Even with other humans, we infer consciousness from behavior, language, and structural similarity—we do not access their subjective states. With non-human species, we rely on neural architecture, functional parallels, evolutionary continuity, and behavioral complexity to guide inference. But the choice to treat these similarities as indicating experiential depth rather than mere mechanism reflects our framework commitment. The continuum makes this choice transparent rather than disguised, but it remains a choice about how to engage with evidence, not a proof about ultimate reality.
Boundaries prove equally uncertain. Where does consciousness fade along the organizational spectrum? We’ve expressed genuine uncertainty about plants—whether distributed systems without clear integration support any experiential quality. The framework keeps such questions open rather than foreclosing them, while remaining confident that elephant, cetacean, and great ape organization clearly supports rich experiential integration. But we cannot specify exactly where sufficient integration begins or ends. This uncertainty about edges doesn’t undermine confidence about peaks; fuzzy boundaries are features of spectrums, not arguments against their existence.
The standards for evaluating consciousness claims differ fundamentally from those appropriate for physics. Falsifiability works brilliantly for closed systems where variables can be isolated and experiments repeated identically. Biology succeeds through different methods—narrative coherence, consilience across evidence types, explanatory power. Consciousness studies require pragmatic evaluation: Does a framework accommodate evidence coherently? Does it generate productive inquiry? Does it lead to better practical outcomes for understanding and treating conscious beings? These questions are answerable, even if not through falsification. The “living as if” approach we’ve proposed provides exactly this evaluation method—judging frameworks by consequences rather than demanding impossible metaphysical proofs.
No single line of evidence presented here proves consciousness in any non-human species. The neural architecture of cetaceans, the problem-solving of corvids, the mourning of elephants—each alone remains subject to multiple interpretations. But together these create a coherent picture more parsimoniously explained by continuum frameworks than by treating consciousness as a rare anomaly requiring precisely human-like conditions. This is how biology succeeds: through convergent lines of evidence, each insufficient alone, together compelling.
We’re making the best case available evidence allows, while remaining open to revision if warranted. This combination of framework commitment and honest uncertainty represents intellectual maturity, not weakness. The alternative—claiming either certainty we cannot possess or agnosticism that ignores compelling patterns—serves neither truth nor the beings whose consciousness we’re attempting to understand.
Two Peaks: Terrestrial and Marine
From the evidence surveyed, two distinct peaks in neural complexity and behavioral sophistication emerge. The terrestrial peak, exemplified by elephants and great apes, demonstrates consciousness manifesting through mammalian neocortical architecture—highly laminated, specialized regions supporting precise sensorimotor control, complex social cognition, and cultural transmission. These lineages achieved large brain sizes relatively recently in evolutionary terms: elephant ancestors reached high encephalization within the last thirty million years, great apes within the last ten million, modern humans within the last few hundred thousand.
The marine peak tells a different temporal story. Multiple odontocete lineages achieved and maintained high encephalization five million years ago—when our proto-human ancestors were just beginning to walk upright—and have sustained it with remarkable stability across geological time. Sperm whales have carried brains weighing up to nine kilograms for fifteen million years. This represents not merely the evolution of large brains but their maintenance across timescales that dwarf human cognitive history. Where human culture accumulates across thousands of years, cetacean lineages have had millions of years to explore what large brains supporting rich consciousness can accomplish in an acoustic, three-dimensional marine environment.
What makes these dual peaks philosophically significant is not merely their existence but their independence. Elephants and cetaceans last shared a common ancestor roughly sixty million years ago, before either lineage evolved large brains. Great apes and cetaceans diverged even earlier. The sophisticated cognitive capacities these groups demonstrate—complex social structures, cultural transmission, self-awareness, behavioral flexibility, long-term memory, coalition formation, symbolic communication—evolved convergently, not through shared inheritance but through separate evolutionary pathways responding to different environmental challenges in radically different media.
This convergence pattern supports the core prediction of continuum frameworks: if consciousness manifests through organization rather than emerging from specific architectures, evolution should discover multiple solutions. The precise form matters less than the organizational capacity for sufficient integration. Terrestrial peak and marine peak represent different implementations of similar principles—large brains supporting extended social networks, cultural learning accumulating across generations, behavioral flexibility responding to complex environments, affective depth enabling long-term bonds.
The temporal dimension deepens this significance. Cetaceans have not merely evolved consciousness but have lived with it far longer than humans have existed. What does millions of years of cultural accumulation, social learning, and experiential integration produce in beings whose reality is fundamentally acoustic, whose societies show stability across decades, whose communication systems support group-specific traditions maintained for generations? We can barely imagine human culture after ten thousand years of cumulative development. Cetacean lineages have had a thousand times that duration to explore what consciousness manifesting in marine environments might become.
This raises what might be called the question of cosmic equivalence: whether Earth has hosted, for millions of years, species whose consciousness is as rich and morally considerable as our own, organized according to completely different principles in an utterly alien medium. If elephants represent consciousness nearly comparable to ours, and cetaceans have sustained comparable or greater neural complexity across far deeper time, the framework suggests we may share this planet with beings who are genuinely our cognitive peers—not aspiring toward human-like consciousness but expressing consciousness as deeply through their own organizational solutions.
Continuum frameworks naturally accommodate rather than struggle with this possibility. If consciousness differentiates through diverse organizations wherever sufficient integration exists, we should expect multiple peaks arising through independent evolutionary experiments. That we find exactly this pattern—terrestrial and marine peaks, achieved through different architectures, maintained across different timescales, supporting comparable sophistication—strengthens confidence in the framework’s explanatory power.
What this means for how we understand consciousness, how we evaluate our responsibilities toward other species, and what the existence of cetacean consciousness reveals about reality itself requires more extended examination than this survey permits. These questions form the center of subsequent inquiry. For now, the evolutionary pattern suffices: consciousness appears to manifest through diverse organizations wherever evolution discovers structures supporting sufficient experiential integration, producing multiple peaks rather than the single anomalous emergence the modern scientific worldview predicts.
Understanding Organization
The evidence surveyed here reveals a pattern: consciousness appears to manifest across diverse neural architectures whenever organization supports sufficient experiential integration. Octopuses with distributed cognition, corvids with enlarged pallium, elephants with massive neocortex, cetaceans with acoustic-processing dominance—each represents a different organizational solution to being a conscious creature in a particular environment. The psychophysical continuum framework naturally accommodates this diversity, predicting multiple peaks rather than singular emergence.
But what exactly do we mean by “organization”? How do brains relate to conscious experience? Why does neural architecture matter, and why might different architectures support comparable experiential depth? These questions require stepping back from specific species to examine how brains construct reality itself.
The concept of umwelt—the species-specific world constructed by each organism’s sensory and neural apparatus—provides crucial insight. Encephalization—the question of brain size relative to body—reveals both its utility and its limitations as a measure. The distinction between neural mass and neural organization clarifies why cetacean brains have been so profoundly misunderstood. These principles, when properly developed, illuminate why the marine peak deserves recognition as genuine cognitive equivalence rather than interesting but secondary phenomenon.
The next chapter develops these foundational concepts before turning to the cetacean case specifically. Understanding how brains relate to consciousness generally—and why different architectures can support comparable sophistication—provides the intellectual framework for examining what cetacean neuroscience reveals and what their behavioral complexity demonstrates. Only then can we properly assess the question of cosmic equivalence and what it means that evolution has produced these two independent peaks in terrestrial and marine environments.