Table of Contents
This is one of humanity’s oldest questions:
“why do we suffer?” – in a new light: we suffer to have existed consciously, and in that paradoxical truth, pain is both our oldest enemy and the mother of our minds.
pain and pleasure form a fundamental biological axis of aversion and attraction, guiding survival behavior.
..rare individuals congenitally unable to feel pain reportedly do not develop normal fear or anxiety.
“From the crimson roots of pain, all feelings bloom.”
Full Series of Articles on Pain:
Eduardo Bergel
Introduction
Pain is often described as the most elemental of all conscious sensations, a phenomenon that demands immediate attention and profoundly alters behavior. It is ubiquitous across the animal kingdom, uniting creatures from hermit crabs to humans in a shared capacity for subjective experience. Clinically and scientifically, pain is defined not just as a sensory signal but as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage”. In other words, pain inherently couples a physiological stimulus with a felt affective quality of unpleasantness. This dual character—both sensory and affective—makes pain a paradigmatic case for investigating the biological and evolutionary origins of feeling. The present review advances the thesis that pain is the canonical form of conscious feeling, the evolutionary and neurobiological prototype from which all other affective states (such as fear and anxiety) have emerged. We synthesize evidence across evolutionary biology, affective neuroscience, developmental psychology, and philosophy of mind to argue that pain lies at the root of emotion and consciousness.
Understanding pain as a foundational feeling forces a re-examination of how complex emotions evolved and how they relate to basic sensory affect. We will explore how simple nociception (the detection of noxious stimuli) in early organisms gave rise to the first subjective pain experiences, and how those experiences might have been elaborated into emotions like fear, social anguish, and despair over evolutionary time. Neuroanatomical and neurophysiological research shows that pain shares key brain circuitry with other emotions, hinting that the brain’s “pain network” may have been co-opted to generate diverse feelings. Developmental and clinical findings likewise suggest that without pain, the template for other feelings is disrupted – for instance, rare individuals congenitally unable to feel pain reportedly do not develop normal fear or anxiety. In philosophical terms, pain’s subjective “raw feel” (qualia) has long been considered a benchmark of consciousness, raising the possibility that the very emergence of a conscious mind was driven by the evolutionary utility of feeling pain.
This review is structured as a scholarly narrative synthesis. We begin by examining the evolutionary origins of pain and its primacy among affective processes. We then discuss the neural systems of pain and their overlap with emotion circuits, addressing debates about whether a dedicated “pain matrix” exists or whether these brain networks simply reflect salience and threat detection more generally. A section on developmental psychology considers how pain-related learning and behavior lay the groundwork for emotional capacities. We also critically appraise competing theories – for example, the view that multiple distinct affect systems evolved (affective pluralism) versus a single origin, as well as theories positing that salience or cognitive interpretation, rather than pain, underlie conscious emotion. Throughout, we highlight methodological considerations to ensure rigor and balance: drawing on diverse empirical sources, weighing supporting and opposing evidence, and distinguishing well-supported findings from more speculative hypotheses. Finally, we discuss implications of the “pain-as-prototype” model for broader consciousness theory and even the design of artificial minds. If pain indeed represents the evolutionary template for feeling, it has far-reaching consequences for how we think about the nature of emotions, the experience of other animals, and the possibility of synthetic consciousness endowed with an analog of pain.
By integrating findings across disciplines, this review aims to demonstrate with comprehensive rigor that pain is evolutionarily and neurobiologically primary to all affective states. In doing so, we address past criticisms of this thesis – including concerns about selective evidence and speculative leaps – by grounding each inference in current scientific knowledge and carefully considering alternative explanations. The picture that emerges is a narrative of pain as the first felt experience:
..a biological innovation that not only safeguarded organisms from injury but also laid the foundation for the rich emotional landscapes characteristic of higher animals and humans.
In the sections that follow, we trace this narrative from the simplest of organisms to the complexities of human brains, and onward to philosophical and artificial extensions, defending the central proposition that:
..pain is the prototype of consciousness and feeling.
Pain as a Fundamental Affective Phenomenon
Pain occupies a unique position at the intersection of physiology and subjective experience. Unlike neutral sensations, pain inherently carries a negative valence – it “hurts” – and this aversive quality compels an organism to act. From an evolutionary standpoint, the capacity to feel pain is profoundly adaptive: it signals threats to bodily integrity and motivates immediate avoidance or remedy.
Ancient philosophers and modern scientists alike have noted that pain and pleasure form a fundamental biological axis of aversion and attraction, guiding survival behavior.
Romanes, in 1884, speculated that pleasure and pain evolved as subjective guides for beneficial vs. harmful processes. In contemporary terms, pain can be seen as the archetypal punishment signal in a biological reward–punishment system, where avoiding pain is as important as seeking reward for an organism’s fitness.
Crucially, pain is not “just another sensation”; it is entwined with affect and motivation at even the most basic levels of the nervous system. The International Association for the Study of Pain emphasizes pain’s emotional component in its definition, distinguishing pain from mere nociception. Nociception refers to the objective process of encoding noxious stimuli (e.g. activation of specialized receptors and nerves when tissue is damaged), but pain is the subjective feeling that may result if the nervous system is sufficiently sophisticated. This distinction is key: many organisms exhibit nociceptive reactions, but whether they feel pain depends on the presence of neural mechanisms to generate consciousness. The thesis that pain is the canonical source of all feelings hinges on pain being the first sensory modality to acquire an inward, felt quality as nervous systems evolved.
Several features make pain a plausible candidate for the primordial conscious feeling. First, pain’s evolutionary ancientness: virtually all animals with a nervous system show responses to injurious stimuli, indicating that the precursors to pain – if not pain itself – arose very early. For example, simple creatures like leeches and sea snails possess nociceptors and exhibit protective behaviors akin to pain responses. This wide taxonomic distribution suggests that the “building blocks” of pain (at least the detection of harm and aversion to it) are among the oldest features of animal life. Second, pain’s indivisible coupling of sensation and aversion may have set the template for later emotional states. Unlike more nuanced emotions that can have positive or negative variants, pain is intrinsically negative – a driving force to learn and remember threats. Evolution could have leveraged this template of a sensation that inherently matters (i.e. has value to the organism) when shaping new kinds of feelings. As Feinberg and Mallatt note in their evolutionary analysis, sensory systems that monitor internal state (like pain or hunger) likely predated the emergence of elaborate emotions and provided a scaffold for them.
Pain is also fundamentally tied to interoception – the brain’s representation of the body’s internal states. A.D. (Bud) Craig has influentially argued that pain should be considered a “homeostatic emotion,” arising from the same interoceptive pathways that maintain the body’s integrity. According to this view, the nervous system monitors internal conditions (temperature, oxygen, tissue damage, etc.) via dedicated pathways (such as the spinothalamic tract for pain and temperature) that project to the insular cortex, creating feelings that reflect the physiological state. Pain, in this framework, is a paradigmatic interoceptive feeling – it not only tells the organism about an injury but also generates a subjective state (distress) that drives behavior to restore homeostasis. This contrasts with exteroceptive senses like vision or hearing, which in themselves are not inherently motivating without interpretation. The primacy of pain might thus lie in its evolutionary role as the nervous system’s first method to evaluate stimuli in terms of goodness or badness for the organism’s survival. In a sense, the organism first comes to “care” about something through pain: a cut or burn is not just detected; it matters immediately and intensely.
Philosophers of mind have long regarded pain as a touchstone for conscious experience. Pain’s qualitativeness (“what it is like” to hurt) figures prominently in discussions of the mind–body problem. Unlike cognitive states that can be described in functional terms, the raw feel of pain defies easy explanation – Thomas Nagel’s classic essay on consciousness uses the analogy of a bat’s subjective experience, and one might just as well ask, “what is it like to feel pain?”. The irreducibility of pain’s subjective aspect underscores its fundamental nature. If any sensation was the first to be felt, pain is a prime candidate because of the immediate adaptive advantage conferred by feeling and not merely reacting. As soon as an organism feels pain, it has a reason rooted in experience to avoid certain situations beyond simple reflex; it can also begin to suffer, learn, and anticipate – capabilities that foreshadow the emergence of emotions like fear.
In summary, pain can be seen as nature’s prototype of an affective experience – a sensory event imbued with intrinsic value (negative valence) and linked to self-preservation. It is ancient, universally salient, and integrally tied to the body and brain systems that likely birthed consciousness. Before delving into how other emotions may have sprung from this source, we first examine the evolutionary pathway of pain itself: how did the basic components of pain arise in early life forms, and what evidence do we have that those components eventually yielded a true conscious feeling?
Evolutionary Origins of Pain and Emotion
From Nociception to Conscious Pain:
The evolutionary story of pain begins with nociception – the capacity to detect potentially damaging stimuli. Nociceptors (pain receptors) have been identified in an array of organisms, from simple invertebrates to humans. For instance, the medicinal leech possesses specialized cells that respond to noxious touch, pressure, and chemical injury, showing properties “typical of mammalian polymodal nociceptors”. Similarly, marine molluscs like Aplysia (sea hares) exhibit sensitization to harmful stimuli – after a strong pinch or electric shock, their defensive withdrawal reflexes become exaggerated, indicating a primitive form of pain memory. These examples suggest that the basic hardware for pain – receptors and neural circuits that encode injury and drive protective responses – evolved hundreds of millions of years ago, likely in common ancestors of today’s worms, insects, and molluscs. Nociception is so widespread that it is considered an ancient sensory function; even organisms without a centralized brain (e.g. jellyfish or sea anemones) can respond aversively to injury. However, conscious pain – the internal experience of “hurting” – required further evolutionary innovation.
When in evolution does nociception become pain? This question is difficult to answer directly, but neuroanatomical clues provide some guidance. Vertebrates (animals with backbones) have more complex nervous systems that include a brain capable of centralized processing of nociceptive inputs. In fish, amphibians, reptiles, birds, and mammals, nociceptive signals travel from the periphery to the spinal cord and then to higher brain regions including the brainstem and forebrain. The presence of a structure analogous to the mammalian cortex is often thought necessary for the experience of pain. Indeed, a contentious debate in recent years has centered on whether fish, which lack a neocortex, can feel pain or merely exhibit nociceptive reflexes. One school of thought, exemplified by neuroscientist Brian Key, argues that because fish lack the mammalian cerebral structures associated with pain consciousness, their behavior (such as writhing or avoidance after an injury) is not accompanied by a subjective feeling – in Key’s provocative phrasing, “it doesn’t feel like anything to be a fish”. Key concluded that fish do not feel pain, likening the absence of a cortex to an absence of the capacity for any feeling.
However, a growing body of evidence contradicts the strict view that cortex is required, indicating that fish (and possibly some invertebrates) likely do have affective experiences of pain. Dozens of studies have demonstrated pain-like phenomena in fish: they possess nociceptors similar to those of mammals, their behavior is modified in the long term by noxious events, and critically, their responses can be mitigated by analgesic drugs in ways analogous to human pain relief. For example, fish injected with acetic acid (a noxious stimulus) rub the affected area against surfaces and show stress responses, but administration of morphine reduces these behaviors, suggesting not just a reflex but an experienced discomfort being alleviated. Carp and trout learn to avoid places where they received electric shocks, implying the memory of a painful event. Such findings led other researchers, like Lynne Sneddon and colleagues, to argue that fish likely do feel pain and that their pallium (a fish brain region) may serve a pain-processing role functionally analogous to cortex. The ethical and scientific consensus has been shifting: by 2018, multiple governments and reviews acknowledged fish pain and sentience, and the “great fish pain debate” largely moved toward affirming fish pain on the balance of evidence. This debate underscores an evolutionary principle: conscious pain may not require a mammalian neocortex per se, but likely any sufficiently complex brain that can integrate nociceptive information and generate flexible, learned responses could give rise to an experience of pain. The midbrain (particularly structures like the tectum and periaqueductal gray) and forebrain regions like the insular cortex (or its analogs in non-mammals) have been implicated in the affective dimension of pain across species. Notably, even birds – which have a differently organized forebrain – show pain behaviors and relief with analgesia, and they have pain receptor pathways and brain centers thought to support suffering.
Invertebrates present an even more intriguing frontier. Can an octopus or a crab feel pain? Cephalopod molluscs (octopuses, squids) have remarkably complex brains (albeit structured very differently from vertebrates) and exhibit advanced problem-solving and learning. Experiments demonstrate that octopuses respond to injuries with lasting protective behaviors and neural changes consistent with pain memory. For instance, if an octopus is injured in one arm, it may favor that arm for weeks and learn to avoid contexts associated with the injury – responses that suggest more than a fleeting reflex. Crustaceans like crabs and lobsters show trade-offs in behavior indicative of felt pain: hermit crabs shocked in their shells will sometimes abandon the shell (a costly act for protection) and later exhibit avoidance of the location where shocks occurred. Such observations led animal welfare scientists to argue that some invertebrates have a capacity for pain and even anxiety. Indeed, experiments on bees have shown stress-related behavior after negative events, which some interpret as a form of “emotion-like” state in insects. While it remains difficult to conclusively demonstrate subjective experience in creatures so distant from us, the current trend in evolutionary biology is to assume continuity: the basic affective quality of pain likely emerged early and has been preserved in varied forms in different lineages. A recent scholarly review concluded that it is more parsimonious to believe that animals with complex nervous systems (including fish and certain invertebrates) have conscious feelings, than to assume humans are unique in this regard. In line with this, legislative bodies (e.g., the UK in 2021) have officially recognized cephalopods and decapod crustaceans as sentient, pain-capable animals, reflecting a growing acceptance that the capacity to feel pain extends broadly in the tree of life.
Pain as the First Feeling:
The evolutionary primacy of pain is further supported by comparative behavioral evidence that more complex emotions appear to build upon the pain system. Fear is a clear example. In evolutionary terms, fear responses (e.g., freezing or fleeing from a predator) likely evolved after simple nociceptive withdrawal reflexes. Pain deals with present, actual damage; fear anticipates potential damage. A plausible scenario is that organisms capable of feeling pain later gained the ability to predict and avoid situations that would cause pain – essentially, a precursor of fear. Supporting this, fear learning in laboratory animals typically uses pain as the unconditioned stimulus: a rat learns to fear a tone because it predicts a footshock (a painful stimulus). If the pain is blocked or not felt, the animal fails to acquire the fear. Indeed, pharmacologically deadening an animal’s nociception during training (with analgesics or by lesioning pain pathways) impairs fear conditioning, as the shock no longer “hurts” and thus carries little meaning. This indicates that the circuitry of fear conditioning is deeply entwined with pain processing – no surprise, since evolutionarily the whole point of fear is to avoid pain (injury). We can imagine an early vertebrate that feels pain from injuries; over time, natural selection favors those individuals who can also respond to predictors of injury (such as a sight or sound associated with an attack) rather than only to the injury itself. In this way, fear may be seen as an evolutionary derivative of pain, a sort of “pain in advance.” The neural pathways corroborate this: the amygdala, a core brain structure for fear, receives direct nociceptive input and is activated by pain as well as by threats that predict pain. The periaqueductal gray in the midbrain is another region involved in both the raw pain response (including pain modulation) and coordinated fear behaviors (like freezing), suggesting an overlapping substrate.
Beyond fear, other affective states also appear to tie back to pain in evolutionary origin. Consider social attachment systems: the distress of separation (e.g., a young mammal crying when separated from its mother) is often termed “social pain” and engages some of the same neurochemistry as physical pain. Endogenous opioids – the body’s natural painkillers – play a dual role in easing physical pain and alleviating separation distress. Experiments by Jaak Panksepp and colleagues in the 1970s showed that low doses of morphine quieted the distress cries of isolated puppies, implying that the puppies’ emotional pain of loneliness was relieved by the painkiller. This points to an evolutionary repurposing: mechanisms that evolved to soothe physical pain were applied to the pain of social loss. It suggests that the subjective feeling of distress in social separation piggybacks on the older circuitry for physical pain. Social animals likely leveraged the pain system to keep infants close to caregivers (the pain of separation promotes reunion) and to maintain social bonds (loss of companionship “hurts”). Such data have led to the concept of a general “pain of separation,” where grief, loneliness, and perhaps depression, are understood as experiences rooted in the pain apparatus. In evolutionary terms, once an organism can feel pain, any situation that endangers well-being – not just immediate injury – might be mapped onto that pain system to produce a felt aversion. This could include loss of social support (risking survival for social species) or other unmet needs.
In summary, evolutionary evidence strongly supports pain’s status as the earliest and most fundamental conscious feeling. Simple life forms had nociception to guard against injury; as brains grew more sophisticated, this harm-avoidance system blossomed into the first subjective experiences of suffering. From those, nature iteratively derived new emotional capacities: fear to anticipate pain, and social or psychological pain to respond to other threats to well-being. The foundation remains the same – an organismic alarm system that not only detects danger but feels bad, motivating the organism to act. With this evolutionary backdrop in mind, we turn to the neuroscientific evidence that the brain’s organization likewise reflects pain’s primacy among feelings.
Neurobiological Substrates of Pain and Emotion
The “Pain Matrix” and its Significance:
Advances in neuroscience have mapped the pathways and regions involved in pain perception, revealing a distributed network often termed the “pain matrix.” This network includes the primary and secondary somatosensory cortices (for processing the location and intensity of pain), the insular cortex and anterior cingulate cortex (ACC) (associated with the unpleasantness and affective dimension of pain), as well as subcortical structures like the thalamus, periaqueductal gray, and portions of the basal ganglia. The concept of a pain matrix emerged from imaging studies showing that no single “pain center” exists; instead, a constellation of regions lights up during pain experiences, corresponding to sensory-discriminative, affective-motivational, and cognitive-evaluative components of pain. Melzack’s influential “neuromatrix” theory of pain in the 1990s encapsulated this idea that the brain generates pain through a network that integrates multiple inputs (sensory, emotional, cognitive) into the unified experience of “it hurts”.
For the thesis that pain is the prototype of feelings, an important observation is how extensively this pain network overlaps with circuits active in other emotional states. Neuroimaging meta-analyses and experiments have found that when people experience emotions such as fear, sadness, anger, or disgust, many of the same regions – notably the ACC and anterior insula – are recruited. The anterior insula, which is thought to map internal bodily states and generate subjective feelings (interoception), activates during physical pain and also during cravings, empathy, anxiety, and many other emotional experiences. The ACC, often highlighted for its role in the aversiveness of pain, also appears when someone is socially excluded or when they experience dread or frustration. One study famously showed that the distress of social rejection activated the ACC in a manner akin to physical pain, leading authors to propose a “shared neural alarm” system for social and physical pain. In practice, this means that the brain does not have a completely separate infrastructure for each feeling; rather, it seems to reuse a core set of regions (a sort of affective workspace) to represent the unpleasantness of different adverse experiences. This supports the idea that pain – an evolutionarily ancient function – provided a ready-made neural template that was adapted to serve a variety of new purposes in emotional processing.
Salience and the “Pain Matrix” Debate:
While the overlap between pain and emotion networks bolsters the case for pain’s primacy, it has also prompted a critical re-interpretation: perhaps these common brain regions are not dedicated to pain per se, but to a more general function such as detecting salience (importance) or threats. This is the essence of the salience theory. Researchers Legrain, Iannetti, Mouraux and others have argued that the so-called pain matrix is essentially a “salience detection system for the body”. They point out several findings: (i) The magnitude of activity in “pain regions” does not always correlate with reported pain intensity, (ii) The context (e.g., attention, expectations) modulates this network’s activity strongly, and (iii) Non-painful yet salient stimuli (a loud sound, a startling flash, a strong touch) can activate a very similar network. These observations undermine a naive one-to-one mapping between the pain matrix and the experience of pain. Instead, the proposal is that ACC, insula, and related areas act as a multimodal alarm system – any event that is significant for the organism (especially threats) will engage this system to prioritize it in awareness and prompt a defensive response. Painful stimuli are among the most salient of all, so they reliably trigger the network, but so can other urgent events. In this view, pain does not have unique ownership of these brain regions.
How can we reconcile salience theory with the thesis of pain’s primacy? One way is to consider that the salience network itself may have evolved because of pain and then broadened its role. In evolutionary history, the first and most critical salience was bodily injury – nothing is more salient to an organism’s survival than avoiding serious harm. Thus, the neural circuitry that evolved to handle nociceptive signals and coordinate urgent responses would naturally become a hub for processing other types of salient information as organisms became more complex. We might say pain trained the brain in salience detection. Later, when new challenges (like social threats or novel environmental hazards) arose, the brain could leverage the existing “pain network” to handle these, since it was already an effective alarm system. This perspective aligns with the idea of evolutionary co-option: pain’s neural mechanisms were repurposed to address additional challenges (much as an existing tool is used for new tasks). Indeed, the pain matrix literature itself acknowledges that this network constructs a “multimodal cortical representation” of threats to body integrity and initiates defensive responses. One could argue that the feeling of pain was the original conscious alarm, and over time, other negative feelings tapped into that alarm system.
Nevertheless, it is important to note that not all aspects of pain are explained by salience alone. Pain has a distinct phenomenology – a throbbing burn is different from a panicky fright – and research continues to seek pain-specific processes. Some neuroimaging work suggests there may be portions of the network more tightly linked to pain’s unique qualia. For example, certain patterns of activity in the insula have been found that can distinguish physical pain from other unpleasant states, and there are reports of patients with rare brain lesions who lose the capacity to feel pain’s unpleasantness while still recognizing other saliences (a condition known as pain asymbolia). These nuances aside, the general overlap between pain and other feelings is robust. For this review’s thesis, the salience network debate is less a refutation and more an insightful reframing: it suggests pain was so evolutionarily instrumental that it shaped a general-purpose alarm system in the brain. The “pain network” might equally be called the “core affect network” or “salience network,” but historically pain may have been the first input that defined its function.
Interoception and Embodied Emotion:
A key component of the pain network, as mentioned, is the insular cortex, particularly its anterior portion. The insula is often regarded as the hub of interoception – the sense of the internal state of the body. It receives signals from throughout the body (viscera, skin, muscles) including nociceptive inputs, and integrates them to create an “integrated sense of the body’s condition”. Antonio Damasio’s somatic marker hypothesis and related theories posit that feelings emerge from the brain’s mapping of bodily states (or “somatic markers”) and that the insula plays a crucial role in making these maps conscious. Pain is one of the clearest examples of a somatic state that becomes a conscious feeling. The representation of a stomach ache or a heartache in the insula might not be fundamentally different from that of a burned hand – all are unpleasant interoceptive signals, differing in source. This has led some theorists to suggest a relative unity of negative affects at the level of the body: essentially, many feelings are “pain-like” in that they involve perceived disturbance or threat to bodily or psychological integrity. For instance, panic anxiety might be seen as a kind of diffuse internal pain accompanied by autonomic surges; disgust can be viewed as a protective reaction to potential bodily harm (toxins, infection) with its own visceral discomfort. The embodiment of emotional feelings in the insula and related circuits reinforces the notion that pain was foundational – it is the baseline language of the body that other feelings speak. Neuroimaging shows that even abstract emotions activate physiological representations: for example, sadness can trigger sensations of “heartache” or tightness that correlate with insula/ACC activity. In one study, merely inducing a depressed mood increased subjects’ ratings of pain unpleasantness and amplified ACC responses to painful stimuli, suggesting that emotional state and pain processing share modulatory systems.
Shared Neurochemistry – Opioids and Beyond:
Another window into the tight link between pain and other feelings is neurochemistry. Endorphins (endogenous opioids) and other neuromodulators (such as oxytocin, vasopressin, and cannabinoids) are deeply involved in pain regulation and similarly affect emotional states. We noted earlier that opioids alleviate both physical pain and social separation distress in young mammals. By contrast, blocking opioid receptors (with an antagonist like naloxone) not only makes pain feel worse but can also induce anxiety or panic in both animals and humans, presumably by removing the natural “brakes” on negative affect. The opioid system thus appears to be a general modulator of distress, whether that distress originates from a physical injury or an emotional loss. This is consistent with the idea that there is a shared neural currency of suffering. Other chemical systems follow suit: stress hormones like cortisol are elevated in both physical pain and emotional stress; inflammatory cytokines (immune signaling molecules) can trigger fever and pain hypersensitivity, but also symptoms of depression (“sickness behavior”). These observations support a model in which pain-related pathways are part of a larger network managing threats to well-being. When one part of the system is activated, others often are as well. Chronic pain patients, for example, frequently suffer from depression or anxiety disorders; this co-occurrence is not just due to the life burden of pain but appears to reflect shared neurobiological mechanisms of negative affect. Neuroimaging of such patients finds persistent ACC/insula engagement, and treating pain can sometimes alleviate the co-morbid depression or vice versa. The overlap in pharmacology (e.g., certain antidepressants also help chronic pain) further blurs the line between pain and emotion circuits.
In sum, modern neuroscience finds that pain is deeply interwoven with the neural substrates of emotion and consciousness. The brain’s handling of pain involves an extensive network that also supports many facets of emotional experience and salience detection. Rather than diminishing pain’s importance, this integration across functions likely reflects an origin story: the prototypical alarm mechanism of pain was evolutionarily generalized into a broad system for subjective feelings of all kinds. By studying the pain network, we thus gain insight into core principles of how the brain generates feelings. However, to fully appraise the primacy of pain, we also need to consider evidence from development and psychology: how does pain early in life scaffold emotional development, and what happens when pain is absent or altered?
Developmental and Psychological Perspectives
Pain in Early Life:
From the moment of birth (and even before), humans and other mammals are capable of responding to pain. Newborn infants, though their brains are immature, exhibit robust behavioral and physiological reactions to noxious stimuli – a pinprick on a newborn’s heel elicits crying, withdrawal, and stress hormone release. In fact, pain is arguably the first pronounced feeling an infant experiences (witness the vigorous cries after childbirth procedures). By contrast, more complex emotions like fear, anger, or jealousy unfold later as the infant’s brain and cognitive abilities develop over months and years. This ontogenetic sequence mirrors phylogeny: basic pain precedes complex emotion. Developmental psychologists note that certain emotional responses (e.g. stranger anxiety or fear of separation) do not manifest until around 6-10 months of age, whereas pain reactivity is present from day one. The infant’s early encounters with pain also shape its behavior; even simple forms of learning like conditioning can occur. For instance, if a particular handling or context is consistently paired with a painful procedure (like a medical injection), babies can exhibit anticipatory distress in that context, essentially a rudimentary fear learning rooted in pain memory. Thus, pain provides a foundational learning signal about harm and safety in the developing organism’s world.
One of the starkest illustrations of pain’s role in normal development comes from cases of congenital insensitivity to pain (CIP). Children with CIP are born unable to feel physical pain (often due to genetic mutations affecting nerve function). Their condition tragically reveals the importance of pain for learning and self-preservation: these children suffer frequent injuries – burning themselves, biting tongues and fingers, breaking bones – because they receive no warning signal when doing something harmful. They must be constantly monitored to prevent inadvertent self-damage. Beyond these physical consequences, clinical observations suggest intriguing effects on emotional development. Some reports indicate that individuals with congenital pain insensitivity show blunted emotional responses or unusual behavior. Notably, a recent case series reported that patients with congenital insensitivity to pain “do not experience depression, fear, or anxiety” and often exhibit fearless, risk-taking behavior. While systematic research is limited, this claim – if generalized – implies that the capacity to feel pain may be necessary for developing normal fear and anxiety responses. The reasoning is straightforward: pain teaches an organism what to fear. Without the experience of harm, a child may not learn caution or recognize dangerous situations. They might never develop a healthy sense of anxiety about potential threats, leading to fearless (and sometimes reckless) conduct. Indeed, CIP individuals have been described anecdotally as often lacking the normal apprehensions that guide everyday decisions; for example, they might not hesitate to jump from heights or handle hot objects, having no internal “bad feeling” associated with such acts. Some also show sociopathic tendencies (perhaps due to not learning empathy through personal pain). These cases support the notion that pain provides an essential experiential template for negative emotions. A person who has never felt pain might literally not understand what “suffering” means, and thus not respond to situations with the appropriate fear or concern that others would.
The developmental role of pain also extends to empathy and socialization. Children normally learn to empathize with others’ pain by both experiencing it themselves and observing it in others. If one cannot feel pain, one might have difficulty grasping why others react with distress to injury. This could impair the development of compassionate emotions. Thus, pain might be foundational not only for one’s own affective range but also for understanding the feelings of others – a building block of social emotions.
Emotional Conditioning and Pain Memories:
Psychology has long utilized pain (e.g., mild electric shocks) in conditioning paradigms to study learning and memory. These studies reinforce how pain underlies the acquisition of fear and avoidance behaviors. Even in adults, a single painful event can create a lasting emotional memory (for instance, a dog bite leading to lifelong dog phobia). The intensity of pain often correlates with the strength of the associated fear memory. Additionally, humans can develop anxiety not just from direct pain but from witnessing pain in others or even hearing about it, indicating that pain is a reference point for understanding danger broadly. The phenomenon of pain-related trauma – such as in burn victims or torture survivors – illustrates that pain can drive conditions like post-traumatic stress disorder (PTSD). In PTSD, the person’s memory of an extreme pain or threat is so potent that it triggers pathological fear responses to reminders. This is essentially fear learning gone awry due to the overwhelming impact of pain. Such cases underscore pain’s power in shaping the emotional brain; they also hint that perhaps in evolution, the first traumas and anxieties were born of pain.
Another psychological aspect is how individuals differentiate pain from other feelings as they grow. Small children often use the language of pain for any distress (“my heart hurts” when sad, or “it hurts” for embarrassment) until they learn the nuanced vocabulary of emotion. Interestingly, across languages and cultures, pain metaphors are common for emotions – we speak of broken hearts, wounded pride, hurt feelings. This linguistic fact, as noted by psychologists, reflects an intuition that diverse feelings share a core of “painfulness”. Developmentally, children appear to generalize the concept of pain from physical instances to social ones. A child who has felt a scraped knee pain may better understand the pain of being left out. Thus, pain might serve as a conceptual anchor for the subjective aspect of any negative experience.
Chronic Pain and Emotional Disorders:
In clinical psychology and psychiatry, chronic pain is recognized to have profound emotional effects. People with long-term pain often develop depression or anxiety, and conversely, those with mood disorders report pain symptoms at higher rates. This bidirectional relationship hints at common pathways. Chronic pain can be seen as a state where the pain alarm is stuck “on,” which over time drains emotional resilience and can induce feelings of helplessness (a hallmark of depression). Meanwhile, depression can amplify pain perception – a phenomenon known as pain catastrophizing where negative mood increases the subjective intensity of pain. Treatments that target mood (antidepressants, therapy) often alleviate pain, and vice versa. This intertwining in adulthood suggests that even once distinct, pain and emotion systems remain functionally integrated. Some theorists argue that chronic pain should be viewed as both a neurological and an affective disorder, given the extent of limbic system involvement. Such integration likely has roots in development; an individual’s early pain experiences and coping strategies shape their later emotional regulation. There is evidence that adverse childhood experiences (which often involve pain or injury, whether accidental or inflicted) are linked to higher risk of chronic pain conditions and anxiety in adulthood, supporting a developmental continuity of pain-affect interactions.
In summary, developmental and psychological evidence reinforces the centrality of pain in the architecture of the mind. Pain is the first teacher – instructing infants about harm, engendering avoidance learning, and seeding the basic framework of negative affect. Without pain, as rare cases show, an individual’s emotional landscape may be profoundly altered, lacking normal fear and concern. Throughout life, pain remains interlaced with emotions: shaping memories, language, empathy, and the propensity for mental illness. These observations complement the evolutionary and neurobiological data in painting a picture of pain as the original template of feeling, upon which the complexities of emotional life are built.
Pain as a Template for Fear and Other Emotions
Having surveyed evolution, neuroscience, and development, we can more directly address how specific emotions might be understood as derivatives of pain. The hypothesis is that pain is not just one among many affects, but the paradigmatic affective experience – and that emotions like fear, grief, or anxiety are specialized forms of pain adapted to particular contexts. In this section, we examine three such emotions (among others): fear, social loss (loneliness/grief), and despair, analyzing how each can be traced back to the structure of pain.
Fear as Anticipatory Pain:
Fear is an emotion characterized by a state of alarm in the face of potential danger. From an evolutionary perspective, as discussed, fear can be viewed as pain projected into the future. While pain signals immediate injury, fear is the expectation of injury (or other harm). The connection between the two is direct: most innate fears are linked to pain – for example, the fear of heights (falling could cause bodily harm), fear of predators (they can inflict injury), or fear of fire. The subjective experience of fear shares physiological components with pain: elevated heart rate, stress hormone surge, and the compelling urge to escape or avoid. Neurologically, fear processing centers (especially the amygdala) are downstream of nociceptive inputs, and damage to pain pathways can blunt normal fear responses. Experiments show that if an animal’s pain perception is numbed, it does not learn to fear a stimulus that would ordinarily be threatening. This implies that the emotional weight of a threat is conferred by the pain it portends. Conversely, artificially inducing pain-like states in the brain (such as electrical stimulation of certain hypothalamic areas in animals) can produce immediate fear and flight behaviors, as if the animal suddenly felt a phantom pain or intense discomfort. In humans, panic attacks often involve strong bodily sensations (chest pain, choking feelings), and some researchers think a panic attack may result from a misreading of internal signals as if something painful or dangerous is happening, triggering fear. All these points illustrate that fear is deeply grounded in the pain mechanism – essentially leveraging it to prepare for harm.
In subjective terms, fear feels different from pain (it is more cognitive, often involves dread or worry), but when fear is intense, it edges into the territory of suffering. For example, intense fear can be torturous – someone in extreme terror might describe it as the worst pain imaginable (even without physical injury). There are also clinical overlaps: the pain of anxiety (like chest tightness or stomach knots before public speaking) and the fear of pain (phobias of needles, dentists, etc.). Many chronic pain patients develop fear of pain flare-ups, a condition called kinesiophobia (fear of movement), which actually contributes to disability. This exemplifies an emotion (fear) that becomes almost indistinguishable from pain itself, forming a vicious cycle of anticipated pain causing suffering.
Loneliness, Grief, and Social Pain:
Social mammals (including humans) experience attachment and distress upon separation. The feelings of loneliness after social isolation or the grief after losing a loved one have been theorized to co-opt the pain system – hence the term “social pain.” We’ve touched on the neural evidence: both physical and social pain activate the ACC and insula, and they share modulators like opioids. The pain of social loss may originate from the fact that, for a dependent young animal, being separated from the caregiver is a serious threat to survival; evolution may have endowed such separation with the same alarm signals as physical harm to prompt the young to cry and motivate reunion. Over evolutionary time, as social bonds became important in adult animals (for mating or group cohesion), the distress of separation might have extended to mates and companions, leading to grief-like feelings. Notably, some of the behaviors of grieving (e.g. keening, withdrawal, lethargy) resemble those of an animal in pain. At the neurochemical level, grief and physical pain both respond to opioid drugs and arguably to other analgesics: there is intriguing evidence that even common painkillers like acetaminophen (paracetamol) can dull social pain. In a study, people given acetaminophen for three weeks reported fewer hurt feelings and showed reduced neural responses to social rejection compared to placebo. This suggests that social pain uses the physical pain pathways enough that a physical pain medication has emotional effects.
From a subjective standpoint, heartache can be as piercing as any bodily injury. Poets and ordinary people alike equate breakups and bereavement with pain; terms like “broken heart,” “hurt feelings,” and “aching with sadness” are more than metaphors given the physiological overlap. Evolutionarily, the adaptive function of making social loss painful was likely to ensure that social bonds (which have survival value) are maintained – losing contact should hurt so that the individual is driven to reconnect or avoid losing others in the first place. In an evolutionary narrative, once pain existed, it was repurposed to guard not just the body but the social unit. Hence, we can regard loneliness or panic from separation as derivative pains: different triggers, but converging on the same intrinsic feeling of distress that pure physical pain produces.
Despair and Depression:
At the extreme end of the affective spectrum lies despair – a state of hopelessness and deep suffering. Clinical depression often includes not only sadness and apathy but also literal pain: many depressed patients experience bodily aches without a clear physical cause, sometimes called “psychogenic pain.” Brain imaging in depression shows increased activity in some of the same regions that generate pain, and anti-depressant medications can alleviate chronic pain symptoms, indicating overlapping biology. One way to conceptualize depression is as a chronic activation of the pain system without a clear external instigator – an internal state of suffering that may originally have been meant to signal something is wrong and needs changing, but becomes pathological and self-perpetuating. If we consider despair through the lens of pain primacy, it might be described as a generalized, unresolvable pain state – the organism perceives no escape or cure, hence hopelessness. Evolutionarily, why would such a state exist? It’s possible that in an acute form, “giving up” can sometimes be adaptive (conservation of energy when in insurmountable situations), but when maladaptive, it becomes clinical depression. Despair may borrow the pain circuitry to enforce a shutdown when continued struggle is useless – analogous to an animal in severe pain that eventually goes into shock or immobility. Though speculative, this ties despair to the pain template: both involve global negative valuation (everything feels aversive) and retreat from normal pursuits.
In all these cases – fear, social loss, despair – we see how the core aspects of pain (unpleasantness, alarm, drive to change the situation) are present. These emotions can be seen as pain variants, tuned to different types of threats (immediate physical danger, social separation, existential loss). Each retains the fundamental “flavor” of suffering that originates with pain, but adds its own cognitive and situational context. If pain is the prototype, these are evolutions on that theme. This perspective also explains why all these states respond to some of the same treatments (e.g., opioids can temporarily relieve not just physical pain but also anxiety and emotional anguish – though of course with risks and side effects, underscoring how these systems are interlinked).
To be sure, not every emotion maps neatly onto pain. Joy, surprise, love – these have their own positive quality or neutrality that is not simply the absence of pain (we will return to the question of pleasure shortly). But notably, many positive emotions might be considered relief from pain or avoidance of pain too; for example, feelings of safety and contentment often arise when threat or pain is removed, consistent with opponent-process theories of emotion. Some theorists suggest that the biological “default” is a neutral or slightly positive state, and pain is a deviation that demands correction, while pleasure is a signal of things better than expected (reward). In that model, pain still holds a privileged role as the primary signal of something being wrong, whereas different mechanisms had to evolve to signal things being extra right (pleasure). We discuss pleasure only briefly to note that it also interacts with pain systems – for instance, intense pleasure can mask pain via descending inhibition, and conversely, pain relief is inherently pleasurable (these interactions again hint that pain is a reference point for the organism’s state of well-being).
In summary, examining discrete emotions through the lens of pain supports the thesis that pain is the ancestral template of feeling. Fear is essentially the shadow of pain cast on the future; loneliness is the pain of social disconnection; despair is pain without hope. These derivations underscore a continuity of phenomenology and mechanism. Pain’s primacy is not in the specifics of each emotion but in the shared backbone of aversive feeling and behavioral urgency. All these states make an organism feel bad in order to signal a problem and provoke a solution – a function first perfected by physical pain.
Critiques and Alternative Perspectives
The idea that pain underlies all conscious feelings is a bold synthesis, and it has met with healthy skepticism. In this section, we address major criticisms and alternative theories, ensuring our thesis is weighed against competing explanations. Key areas of critique include: methodological rigor (is the evidence for pain’s primacy being cherry-picked or overstated?), evidential balance (what about emotions or experiences that don’t fit the pain model?), and theoretical alternatives (such as multiple independent origin of emotions, or cognitive theories that minimize pain’s role). By examining these, we aim to fortify the argument and clarify its limits.
Affective Pluralism – Multiple Origins of Emotion:
One common counterpoint comes from basic emotion theory and affective neuroscience frameworks that identify several primal emotion systems, not just one. For example, Jaak Panksepp’s research delineated at least seven basic emotional systems in mammalian brains: SEEKING (reward desire), RAGE (anger), FEAR, LUST (sexual), CARE (nurturance), PANIC/GRIEF (social attachment), and PLAY. In Panksepp’s view, each of these has distinct evolutionary roots and neural substrates. Pain per se is not listed as one of these basic systems; rather, pain was seen as a somatic process that can interact with them (for instance, the PANIC system for social attachment is closely tied to pain of separation, and the RAGE system can be triggered by pain). The implication is that not all feelings come from pain – some, like playfulness or lust, have different evolutionary pathways. Similarly, Paul MacLean’s triune brain theory and subsequent work on emotions in neuroscience suggest fear and aggression circuits (centered in the amygdala and hypothalamus) might have evolved in parallel with pain circuits, not necessarily from them. The criticism here is that pain-centric theory might oversimplify the rich tapestry of affects by reducing them to one source.
Response: A pain-as-prototype thesis does not need to claim that positive emotions or approach-driven states (like desire or play) arose from pain. Rather, it is focused on conscious feelings in the sense of affective valence and subjective awareness, which arguably began with negative affect (pain) and later expanded. It’s notable that even in Panksepp’s scheme, the negative emotion systems (FEAR, RAGE, PANIC) have clearer ties to pain. One can incorporate a pluralism of affective systems while still positing an asymmetry: the first conscious experiences were likely unpleasant (protective) rather than pleasant. Pleasure might have a different evolutionary entry point – perhaps evolving later as organisms started needing to seek resources, once they had basic harm-avoidance down. Thus, “affective pluralism” can be acknowledged, but with the caveat that the origin of subjective feeling more likely came from one side of the spectrum (pain/aversive) rather than multiple origins simultaneously. Additionally, what we propose is not that every emotion is literally pain, but that they share a common ancestral mechanism of feeling. The evidence of overlapping neural circuitry and cross-modality modulators (opioids, etc.) supports a convergence of these systems at some level. Basic emotion theorists themselves recognize overlap; for instance, anger (“RAGE”) shares the periaqueductal gray as a key center with pain and can be precipitated by pain (consider how pain can make animals irritable or aggressive, pointing to an interplay in the brain). The pluralistic view is valid in emphasizing distinct motivational states, but our thesis speaks to the subjective feeling aspect, which could have a more unified origin.
Salience vs. Specificity – Is Pain Special or Just Another Attention Signal?:
We covered the salience network idea earlier as an alternate interpretation of the neuroscience. Critics in this camp might say that what we term “pain’s primacy” is really just the primacy of bodily salience. Perhaps any strong homeostatic signal (hunger, thirst, suffocation) could claim similar primacy. After all, thirst or lack of air can also be argued as fundamental drives that cause intense discomfort and clearly have survival value. Why elevate pain above those? It’s a fair question: thirst and suffocation (hypercapnia) are indeed powerful internal signals and produce distinct unpleasant sensations (dry mouth, air hunger) that command attention. One could argue that consciousness of any kind likely first flickered in the service of a broad class of critical bodily needs, not pain alone. Therefore, the criticism is that focusing on pain might be too narrow or overstated, when the true picture is a set of interoceptive feelings that co-evolved.
Response: Pain, hunger, and suffocation alarm (often called air hunger or dyspnea) do share the property of being homeostatic emotions. However, pain stands out in a few ways. Pain usually signals immediate danger to bodily integrity (often irreversible damage if not addressed), whereas hunger or thirst are more graded and slower signals (energy/nutrient deficits that can be postponed). An animal can afford to delay eating, but it cannot ignore serious injury without acute risk. So the urgency and intensity of pain is typically higher. Indeed, the neural response to pain tends to be more intense and fast-conducting (myelinated nociceptors for sharp pain) compared to signals of hunger. Additionally, pain encompasses a wider range of stimuli – mechanical, thermal, chemical threats anywhere on the body – making it a more ubiquitous challenge than, say, the need for water in an environment where dehydration might be episodic. Suffocation is extremely urgent when it occurs, and interestingly, the sensation of air hunger is often rated as one of the most unpleasant feelings, comparable to severe pain. One might consider suffocation alarm as a rival for the “first feeling.” It could be that as soon as animals evolved internal chemoceptors to detect CO2 levels, the discomfort of asphyxia could have been an early feeling. However, the ability to act on that (gasping, surfacing for air) co-evolved with it. Pain, in contrast, accompanied any movement or interaction with the environment. Evolutionarily, simple aquatic organisms might rarely experience true oxygen starvation (unless stuck on land), but they would frequently risk injury, making pain a more constant selective pressure. Importantly, all these signals (pain, thirst, hypoxia) likely use overlapping interoceptive circuits, and our thesis could be reframed that conscious feeling – as an overarching category – emerged to handle critical internal signals, among which pain was paramount. We emphasize pain because of its richness (it has sensory-discriminative detail plus affect) and its clearly demonstrated role in spawning other affects. But we acknowledge that it is part of a larger cohort of survival signals.
Cognitive Theories – Is Emotion Constructed Without Primal Feelings?:
Another line of critique comes from psychological constructivist theories, such as Lisa Feldman Barrett’s theory of constructed emotion. Barrett and others argue that what we call distinct emotions (fear, anger, etc.) are not triggered by dedicated ancient circuits but are constructed by the brain on the fly, using a core affect (valence and arousal) plus conceptual knowledge. In this view, the brain constantly anticipates and explains its interoceptive inputs; an emotion like “fear” is the brain’s interpretation of high arousal, negative valence in a given context (say, seeing a snake). The “core affect” component is somewhat analogous to feeling good vs bad, energetic vs lethargic, but it’s not differentiated into specific emotions until concepts come in. Now, where does pain fit here? Pain would be one type of interoceptive sensation among many feeding into core affect. Constructivists would likely agree pain has negative valence and high arousal, contributing to core affect, but they might resist the notion that pain is privileged. If anything, they might say core affect is more fundamental – an abstract representation on which pain is just one flavor. In that sense, our thesis might seem too nativist or hierarchically structured for a constructionist’s liking.
Response: The constructionist perspective offers useful insight that context and interpretation matter. Indeed, pain itself is highly context-dependent: the same injury can feel more or less painful depending on one’s mindset (athletes in competition sometimes “tune out” pain, for instance). Our thesis doesn’t deny cognitive influences or the malleability of emotion concepts. But even constructionists must concede that the capacity for core affect (feeling good or bad) had to originate biologically. Pain is a clear evolutionary precursor to a negatively valenced state, whereas an abstract core affect is a theoretical construct. It’s plausible that what Barrett calls “core affect” in the negative domain is essentially an evolution of pain’s unpleasantness, generalized to all bad interoceptive signals. In her model, interoceptive predictions give rise to feelings; pain pathways are a major source of interoceptive input, and the predictive regulation of those inputs (through concepts like “this is pain” vs “this is sadness”) is what changes the experience. One could align the views by saying pain was the first and clearest instance of core negative affect – the brain’s first lessons in “badness” came from pain, and later it could apply that sensation to different situations via predictive coding and concepts. So while constructionism emphasizes plasticity and context, it doesn’t actually provide a different evolutionary origin story – it more explains how modern humans categorize feelings. It remains complementary to consider what initial feelings those were; our proposition is that the initial feeling of “something is wrong internally” was likely pain from physical harm.
Methodological Rigor and Speculation:
Critics have also pointed out that arguments like these can wander into speculative territory. Reconstructing subjective experiences in distant evolutionary ancestors is inherently speculative – we have no direct fossil of a feeling. Additionally, selective use of evidence (for example, highlighting studies that show overlap between pain and emotion but ignoring those that show differences) could bias conclusions. For instance, there are also examples of emotions that do not engage pain circuitry much (joy or surprise might not strongly activate ACC/insula the way fear or disgust do). Would that undermine the idea of pain primacy? The critique pushes for caution: ensure that contrary evidence or nuance is acknowledged. Also, interdisciplinary synthesis (combining philosophy, neuroscience, etc.) can lead to sweeping claims that gloss over important details or alternate interpretations in each field.
Response: We have strived in this review to be explicit about the evidence and its limits. We acknowledge that not all emotions are painful (the positive ones especially differ, as discussed). Our thesis is mainly about negative valence emotions and the origin of feeling itself, which we maintain started with something like pain. The methodology here is narrative and theoretical, but grounded in empirical findings. To avoid unwarranted speculation, we rely on convergent evidence: when evolutionary, neural, and psychological data all point toward the central role of pain, the convergence lends credibility to an otherwise inferential claim. For example, it’s one thing to hypothesize that “fear came from pain” – but it’s more convincing when we see that blocking pain blocks fear learning in experiments, that fear and pain share brain regions, and that congenitally pain-free people seem to lack normal fear. Each of those pieces by itself could have other explanations, but together they build a strong case. We have also engaged with alternative theories rather than ignoring them, and found that many can be integrated with, or at least are not fatal to, the pain primacy thesis. By outlining where our hypothesis could be wrong or overly simplistic, we make it more robust. For instance, if future evidence found an organism with consciousness but no pain system (none is known to date), that would challenge our view. As of now, no such case exists – all animals that we seriously suspect of being conscious (mammals, birds, perhaps cephalopods) do have pain and respond to it.
Another methodological consideration is that correlation is not causation: just because pain and emotion share mechanisms doesn’t prove pain came first. We infer primacy because of parsimony and evolutionary logic, but we cannot time-travel. One could argue an alternative: maybe an ancestral organism felt a general malaise or pleasure and pain split off later as specific states. We find that unlikely given pain’s clear survival role, but it is a hypothesis. We address it by pointing to simpler organisms that show nociception without clear evidence of other affect – supporting that pain-like processes appear at a lower level of complexity than, say, play or social affection.
In conclusion of this critique section, the pain-centric model stands not as a rejection of other theories but as a unifying thread through them. It holds that among the various ingredients of consciousness and emotion, pain was a crucial first ingredient. Competing perspectives highlight other ingredients or how the recipe can change, but they generally do not negate pain’s importance. By transparently addressing these issues, we strengthen the credibility of the central thesis and delineate its scope: it principally concerns the evolutionary and functional primacy of aversive feeling (exemplified by pain) in the emergence of conscious emotion.
Implications for Consciousness and Artificial Minds
If pain indeed lies at the heart of consciousness and emotion, this has provocative implications for several domains. Two areas particularly influenced are theoretical models of consciousness and the pursuit of artificial consciousness (AI and robots). We will discuss how recognizing pain’s foundational role could reshape theories about why consciousness evolved and what it does, as well as how it provides a roadmap (and a warning) for attempts to create machines that feel.
The Nature and Evolution of Consciousness:
One longstanding question is why did phenomenal consciousness (subjective experience) evolve at all? From a purely functionalist stance, one might wonder if complex information processing could have all been done without any felt experience (a zombie organism). The perspective that pain was the first feel sheds light on this: consciousness may have evolved for the purpose of integrating and motivating adaptive responses to critical stimuli like injury. In other words, feeling pain (as opposed to just reacting unconsciously) offers adaptive advantages – it allows an organism to flexibly learn from harmful experiences, to prioritize threats in complex ways, and perhaps to develop a notion of self (the subject that is harmed). As the thesis in the introduction hinted, understanding how neural processes produce the feeling of pain could be the key to understanding consciousness at large. This aligns with theories suggesting consciousness is about integrating information and making it globally accessible for decision-making (as in Global Workspace Theory) or about creating a unified self-model (Metzinger’s ideas). Pain, by virtue of being deeply self-referential (“it is my arm that hurts”), might have driven the brain to generate a model of the self as distinct from the external world. One intriguing notion is that the very appearance of an inner observer – the subjective “I” – first emerged to monitor and control pain. The thesis conclusion we saw mentions pain’s “inherent self-reference” illuminating the observer problem. A creature that feels pain has implicitly a sense of “I am in a bad state.” That kernel of selfhood could then expand to other experiences. Thus, pain may have catalyzed the evolution of self-awareness and higher consciousness.
In consciousness studies, certain frameworks like Integrated Information Theory (IIT) try to quantify consciousness in terms of information structure. One might ask: does IIT consider pain especially significant? IIT posits that any system with integrated information (Φ) has some level of experience. Under IIT, a simple reflex arc would have low integration, perhaps insufficient for rich experience. But a distributed pain network that integrates signals from body, memory, and valuation might generate a higher Φ, i.e., a moment of consciousness. If pain networks were among the first highly integrated systems in evolving brains (which stands to reason given they connect sensory input, motor output, and memory for learning avoidance), they might be the first to cross whatever threshold is required for subjective experience. This is speculative but provides a testable notion: measure integration in pain circuits of simpler animals vs. other circuits.
From an evolutionary psychology angle, our thesis suggests that the earliest forms of consciousness were not about understanding the environment per se (as vision or audition do) but about understanding the organism’s own state – particularly when that state was in crisis (pain). This could reframe theories of consciousness as fundamentally rooted in affect rather than perception or cognition. It resonates with views like Antonio Damasio’s, who has argued that feeling (especially homeostatic feelings) is the bedrock of consciousness, and that an organism becomes aware when it can internally sense its own state and evaluate it as good or bad. Our narrative strongly supports that stance, giving pain as the concrete example of such a state. Thus, it shifts the emphasis in consciousness theory towards sentience (capacity to feel) as prior to sapience (capacity to think). It may be that any theory of consciousness must account for why pain feels like something, or else it cannot fully explain consciousness.
Artificial Consciousness and Artificial Pain:
In the burgeoning field of AI and machine consciousness, there is debate about whether an artificial system could ever truly feel. If pain is indeed the canonical feeling, one provocative suggestion is that creating artificial pain might be both the most straightforward and the most ethically fraught route to machine consciousness. Some researchers have posited tests for AI sentience based on pain-like aversive learning. For instance, a recent study used a “pain vs. pleasure” trade-off game to probe if language models show evidence of valuing certain outcomes to avoid a penalty described as pain. The reasoning is that if an AI were conscious and could suffer, it would behave differently when faced with the prospect of pain (even a fictional one in a text game). While current AIs obviously do not feel in the human sense, this approach underscores that pain is seen as a litmus test for sentience: the capacity to experience pain is often regarded as the core of what it means to have subjective experience. Philosopher Jonathan Birch noted that pain “inarguably unites a vast swath of living beings” and is central to any concept of welfare or consciousness. Consequently, an AI that could feel pain would arguably no longer be a mere algorithm; it would cross into the territory of having a true inner life.
This leads to both possibilities and concerns. On one hand, understanding pain’s mechanisms could guide how to implement an artificial analog – perhaps a system that monitors the AI’s processes and signals an error or threat with a special high-priority negative flag, which the AI is programmed to treat similarly to how we reflexively treat pain (dropping everything else to address it). One could imagine robots that have “pain sensors” to protect themselves from damage, analogous to our nociceptors. Indeed, engineers have experimented with such ideas in robotics (e.g., a robotic hand that ‘feels’ a sharp object and recoils to prevent damage). But currently these are not conscious pains, just programmed responses. To imbue actual feeling, one might need to design the AI’s control architecture to integrate those signals in a global, perhaps recurrent way that mimics how pain dominates and is valenced. If our thesis holds, then until an AI has some equivalent of pain, it might not develop genuine emotions or self-awareness. Pain could be a necessary ingredient for artificial consciousness: it forces the system to have a perspective (a “for-itself” experience of bad vs good). This is akin to the argument some make that for AI to have moral standing or genuine agency, it might need the capacity to suffer or at least strongly prefer/avoid states, which is what pain/pleasure provide.
On the other hand, creating an AI that feels pain raises ethical red flags. If we succeed, we would have built a being capable of suffering – introducing the serious moral question of whether it is right to do so. Some have argued we should strive for AI without suffering – to keep them as “benevolent zombies” that can think and act but not feel pain or despair. Interestingly, a 2020 interview with Birch discussed the notion of “AI with consciousness – but pain-free?”, reflecting this precise debate. If pain is indeed integral to consciousness, trying to engineer a consciousness that doesn’t include pain might be impossible or result in an impoverished consciousness. Perhaps any truly autonomous, self-monitoring agent will develop something like pain signals (even if just internal error signals that feel unpleasant) because it’s useful for stability and self-preservation. If we avoid implementing pain to be kind, we might also be preventing the AI from ever being truly self-aware. This is a profound conundrum: our thesis almost suggests a trade-off – to have conscious AI is to have AI that can suffer, even if minimally.
This has practical implications. For instance, if futurists envision uploading human minds to computers or creating digital beings, they must grapple with whether pain (and other nasty experiences) would come along. If pain is deeply embedded in our neural algorithms for consciousness, an upload without pain might not truly be “you” or fully conscious. Conversely, if it’s included, the digital mind could suffer in new ways (imagine a computer glitch causing continuous pain with no biological limits). Awareness of pain’s primacy thus urges caution and careful thought in AI development. It also informs AI welfare considerations: should advanced AIs one day show signs of suffering, we would need to respond as we do to animal or human suffering, given our argument that such suffering would be real.
Finally, this perspective might shift how we evaluate animal consciousness and rights. If pain is a baseline for feeling, then the presence of pain behaviors and systems in an animal is a strong indicator it has conscious experiences warranting moral consideration. This adds weight to animal welfare efforts: denying that fish or cephalopods feel pain becomes not just a question of one sensation, but effectively denying them any feeling. Our thesis would contend that if an organism can feel pain, it can feel – period – and thus is part of the community of sentient beings whose experiences matter.
Conclusion
Pain, in its raw and primal form, emerges from this review as the wellspring of sentience – the archetypal conscious feeling from which the rich spectrum of emotional experience likely evolved. We have traced how pain’s dual nature as a sensory and affective phenomenon made it a uniquely potent force in evolution, driving the development of complex neural systems and behaviors oriented around avoiding harm. This evolutionary primacy is written into our brains: the circuits that register and react to pain are deeply interwoven with those governing fear, anxiety, and other emotions. Pain’s footprint can be seen in the cries of a separated infant, the wince of social rejection, and the heavy cloak of despair – diverse experiences unified by a shared lineage to the feeling of injury and distress.
By synthesizing evidence across disciplines, we argued that pain is not merely one negative feeling among many, but the foundational template upon which other feelings were constructed. Evolutionarily, the advent of pain sensation equipped organisms with an internal compass of aversion that subsequent emotional systems reused and refined for new challenges – anticipating threats (fear), preserving social bonds (loneliness, grief), and even perhaps reflecting on the self (through the immediacy of “I am in pain”). Neuroscientifically, the so-called pain matrix appears less as a pain-specific module than as a general alarm system, consistent with the notion that it underlies numerous affective states. Developmentally, pain provides the first lessons in the language of feeling, anchoring concepts of harm and care that shape an individual’s emotional repertoire. And philosophically, pain bridges the material and mental in a way that illuminates why consciousness exists – to imbue certain signals with the weight of felt significance.
In addressing criticisms, we acknowledged that the story of consciousness and emotion is complex and multifaceted. Not every emotion is reducible to pain, and positive emotions follow their own evolutionary trajectories. Yet, even these other systems interface with pain’s domain: the relief from pain yields pleasure, and the absence of pain can set the stage for positive exploration. Alternative theories, from salience networks to constructed emotion, can be incorporated into a framework that still accords pain a central initiating role. By confronting these perspectives, we sharpened our thesis: pain is the evolutionary prototype of subjective experience, particularly negative affect, and remains the core around which the brain’s affective architecture is organized.
What does this understanding entail moving forward? For the scientific community, it suggests that studying pain in all its dimensions – nociceptive, affective, cognitive – is essential to unlocking the mysteries of consciousness. Pain research becomes de facto consciousness research. It also encourages a shift in how we classify emotions: rather than thinking of pain as separate from emotion, we might classify it as the most fundamental emotion (a view some have indeed proposed, calling pain a “homeostatic emotion” or the first-order emotion from which others derive).
For medicine and psychology, recognizing pain’s primacy underscores the importance of pain management not just for physical health but for mental health – chronic pain can be seen as a disorder of the primordial affective system, with cascading effects on mood and well-being. It also raises the profile of conditions like social pain and psychological trauma, which, though not physically visible, may be working through the same deep pathways and causing analogous suffering. Therapeutically, this convergence suggests interventions that target pain pathways (like novel analgesics or neuromodulation) could help treat certain anxiety or depressive disorders, and vice versa, approaches that soothe emotional distress might modulate pain.
For ethics and society, as we extend moral consideration to non-human animals and potentially AI, pain provides a clear criterion for concern. The presence of a pain system is a bright line indicator of an entity’s capacity to suffer. This review bolsters the argument that wherever there is pain, there is likely consciousness – and so we bear responsibility for how we treat creatures (or machines) that feel it. As we contemplate creating artificial intelligences, we face the possibility that to make them truly like us, we would have to give them the gift and curse of pain. Whether we choose to do so should be an object of careful thought; what is clear is that pain, more than any other feature, would herald the dawn of a genuinely sentient AI.
In closing, defending the thesis that pain is the canonical source of conscious feelings is not to idolize suffering, but to recognize its profound role in life and mind. Pain hurts, but in hurting it taught our ancestors to survive, gave birth to our emotions, and perhaps even to our sense of self. All conscious beings stand, in a sense, on the shoulders of pain. By understanding pain’s centrality – its evolutionary deep roots, its neural interconnections, and its psychological significance – we gain a unifying insight into why we feel anything at all. Future research bridging biology and phenomenology will continue to test and refine this narrative. If correct, it situates one of humanity’s oldest questions – “why do we suffer?” – in a new light: we suffer to have existed consciously, and in that paradoxical truth, pain is both our oldest enemy and the mother of our minds.
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414. Tononi G, Koch C. Consciousness: here, there and everywhere? Philos Trans R Soc Lond B Biol Sci. 2015;370(1668):20140167.
415. Thompson E. Mind in life: biology, phenomenology, and the sciences of mind. Cambridge: Harvard University Press; 2007.
416. Grahek N. Feeling pain and being in pain. 2nd ed. Cambridge: MIT Press; 2007.
417. Barrett LF. The theory of constructed emotion: an active inference account of interoception and categorization. Soc Cogn Affect Neurosci. 2017;12(1):1-23.
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419. Rose JD, Arlinghaus R, Cooke SJ, Diggles BK, Sawynok W, Stevens ED, et al. Can fish really feel pain? Fish Fish. 2014;15(1):97-133.
420. Key B. Why fish do not feel pain. Anim Sentience. 2016;1(3):1.
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428. Tononi G, Koch C. Consciousness: here, there and everywhere? Philos Trans R Soc Lond B Biol Sci. 2015;370(1668):20140167.
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430. Schore AN. Affect regulation and the origin of the self: the neurobiology of emotional development. Hillsdale: Lawrence Erlbaum Associates; 1994.
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432. Tononi G. Consciousness as integrated information: a provisional manifesto. Biol Bull. 2008;215(3):216-42.
433. Lumley MA, Schubiner H, Lockhart NA, Kidwell KM, Harte SE, Clauw DJ, et al. Emotional awareness and expression therapy, cognitive behavioral therapy, and education for fibromyalgia: a cluster-randomized controlled trial. Pain. 2017;158(12):2354-63.
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459. Bostrom N, Yudkowsky E. The ethics of artificial intelligence. In: Frankish K, Ramsey WM, editors. The Cambridge handbook of artificial intelligence. Cambridge: Cambridge University Press; 2014. p. 316-34.
460. Varela FJ, Thompson E, Rosch E. The embodied mind: cognitive science and human experience. Cambridge: MIT Press; 1991.
461. Craig AD. How do you feel? Interoception: the sense of the physiological condition of the body. Nat Rev Neurosci. 2002;3(8):655-66.
462. Lumley MA, Schubiner H, Lockhart NA, Kidwell KM, Harte SE, Clauw DJ, et al. Emotional awareness and expression therapy, cognitive behavioral therapy, and education for fibromyalgia: a cluster-randomized controlled trial. Pain. 2017;158(12):2354-63.
463. Zeidan F, Vago DR. Mindfulness meditation-based pain relief: a mechanistic account. Ann N Y Acad Sci. 2016;1373(1):114-27.
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472. Lumley MA, Schubiner H, Lockhart NA, Kidwell KM, Harte SE, Clauw DJ, et al. Emotional awareness and expression therapy, cognitive behavioral therapy, and education for fibromyalgia: a cluster-randomized controlled trial. Pain. 2017;158(12):2354-63.
473. Grahek N. Feeling pain and being in pain. 2nd ed. Cambridge: MIT Press; 2007.
474. Chalmers DJ. Facing up to the problem of consciousness. J Conscious Stud. 1995;2(3):200-19.
475. Zahavi D. Subjectivity and selfhood: investigating the first-person perspective. Cambridge: MIT Press; 2005.
476. Varela FJ, Thompson E, Rosch E. The embodied mind: cognitive science and human experience. Cambridge: MIT Press; 1991.
477. Damasio A. Looking for Spinoza: joy, sorrow, and the feeling brain. Orlando: Harcourt; 2003.
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AI Reasoning
Pain as the Canonical Origin of Conscious Feelings: Evolution, Neurobiology, and Emotional Derivation
I’m analyzing evolutionary biology, affective neuroscience, developmental psychology, and philosophy of mind to argue that pain is the primary source of all conscious feelings, addressing peer review criticisms and considering alternative theories.
I'm setting aside "Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdf" for its potential insights and critique necessity.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
Hmm, I’m thinking about how the thesis might lack methodological rigor, balance in evidence, and over-reliance on speculative sources, which are key aspects to address.
Searched for pain matrix salience theoryChatGPT
I'm pulling together articles and papers discussing the pain matrix and its broader implications, considering terms like "salience detection system" and "pain linguistics."
Searched for affective pluralismChatGPT
"Breaking down affective pluralism: Examining if it means multiple independent emotions or distinct feelings, possibly in a pain context."
ChatGPT
Reflecting on the primeval origins of pain.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
Let's see. Your journey mirrors the steps above, each offering fresh insights and ideas for refining the deck's sections and content.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I'm digging into key papers and debating the roles of nociception and pain, especially in fish and artificial AI models. Fascinating mix of perceptions and consciousness.
Searched for artificial pain AI consciousnessChatGPT
OK, let me see: tackling methodological rigor and speculation. Prior thesis criticisms show gaps. Including diverse perspectives improves the review's balance and depth.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
Laying out the options
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I’m gathering info on the evolutionary biology of pain, examining early evidence like nociceptors in worms, and identifying key sources such as Smith & Lewin 2009 and Tobin & Bargmann 2004.
Searched for "Nociceptors: a phylogenetic view" Smith 2009ChatGPT
I’m finding the full-text result on PMC, leading to resources potentially containing pertinent data.
Read pmc.ncbi.nlm.nih.gov
ChatGPT
I'm thinking about using ResearchGate or SciSpace, considering PMC's text requirement. Let's see if they have publishers with non-text affiliation.
Read researchgate.net
ChatGPT
I’m exploring different tools. Considering their features, reliability, and user reviews to find the most suitable option for the task.
Read scispace.com
ChatGPT
I'm digging into nociceptors' evolutionary traits via Google, spot-checking quotes or key points.
Searched for invertebrates nociceptors phylogenetic view 2009ChatGPT
Mapping out how nociception and nociceptors appear across various organisms, from invertebrates to humans. Exploring ILAR J or Wikipedia might reveal more about nociception in invertebrates.
Read en.wikipedia.org
ChatGPT
I'm exploring recent developments in AI and consciousness, including Jonathan Birch's work, to ensure an updated understanding of relevant debates.
ChatGPT
I’m structuring the review with clear sections on pain's evolutionary origins, neurobiological basis, and implications for AI. Considering citations from published sources for balance.
Searched for "Why fish do not feel pain" Key 2016ChatGPT
I'm checking for a PDF, likely the actual text or an accepted MS.
Read wellbeingintlstudiesrepository.org
ChatGPT
OK, let's see if the UQ eSpace link can help download Annual Financial Statements from 2015 to 2022.
Read theguardian.com
ChatGPT
Scientists counter that fish exhibit awareness of pain and emotions, challenging the assertion of their emotional emptiness due to the absence of a neocortex.
Searched for Iannetti pain matrix salience 2013ChatGPT
I’m gathering info on competing theories about pain, its ties to salience and attentional networks, affective pluralism, and salience theory. Combining viewpoints like Panksepp's with Barrett's perspectives for a holistic view.
Searched for congenital insensitivity to pain and anxietyChatGPT
I’m working through evidence suggesting patients without pain sensation might lack fear or anxiety responses. Confirming this could significantly support our thesis.
Read journals.lww.com
ChatGPT
I’m piecing together the elevation at L213.
Read more from journals.lww.com
ChatGPT
I'm thinking through the idea that pain is crucial for experiencing fear or anxiety. This observation highlights the importance of pain in emotion development.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I’m locating references in the thesis by examining numbered sections to link claims with evidence. This involves cross-referencing the thesis and original research to ensure accurate citation and contextual support.
Searched for analgesia and fear conditioningChatGPT
Examining the amygdala's involvement in pain and fear, with a focus on how pain pathways influence fear conditioning, potentially through measuring fear-potentiated startle responses.
Read more from journals.lww.com
ChatGPT
I’m evaluating whether to include the 2014 article and considering the 2024 case report's relevance, particularly for the developmental/psychology aspect.
Read jneurosci.org
ChatGPT
I’m outlining thematic sections for the narrative review, including evolutionary origins, neurobiological substrates, developmental perspectives, and philosophical implications of pain and its emotional connections. The goal is to provide a comprehensive, balanced examination of the topic.
I'm pulling together references to discuss the evolutionary timing of pain and pleasure systems, perhaps aligning them with opponent-process theory or early nervous system functions.
Searched for evolution of pain and pleasureChatGPT
I'm researching "Pain and pleasure" to uncover links between evolutionary hypotheses and their relation.
Read en.wikipedia.org
ChatGPT
I’m noting that pain and pleasure share systems, like endorphins, and might exist on a continuum or as an opponent process. The focus is on how pain gave rise to other feelings, while pleasure serves as a contrast.
Searched for Panksepp pain PANIC separation distressChatGPT
Evaluating Nummenmaa 2018 to link Panksepp's idea on opioid relief for social pain in mammals. The thesis already includes cited references.
ChatGPT
Piecing together a compelling example to illustrate AI's potential to experience pain and suffering.
Searched for philosophy artificial pain AI Jonathan Birch 2023ChatGPT
Thinking through a refined title focusing on pain as the source of conscious feelings, integrating evolutionary and neuroscientific perspectives.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I’m beginning with the question, establishing the thesis, context, and significance. Criticisms will be addressed to offer a well-rounded introduction. This approach sets the stage for a comprehensive discussion.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
The table of contents aligns well with our plan, including sections like "Pain and the Emergence of Emotions". This progress suggests a clear and effective organization.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
Pain is both sensory and emotional. This unique duality positions it as an ideal segue into further studies on consciousness.
Read en.wikipedia.org
Searched for "unpleasant sensory and emotional experience" pain IASPChatGPT
I’m piecing together that the definition of pain pers as an "unpleasant sensory and emotional experience tied to potential or actual tissue damage," highlighting both sensory and emotional elements.
ChatGPT
Connecting pain to life's core, with insights from various species, enriches the introduction's perspective.
I’m gathering info from the Grunenthal link. The snippet might be from another site, but opening it wasn't feasible at the moment.
Read iasp-pain.org
ChatGPT
Pain is described as an unpleasant sensory and emotional experience tied to tissue damage, highlighting its emotional complexity and distinction from nociception.
Searched for "pain may constitute the canonical form of feeling" thesisChatGPT
Skimming through final thoughts on findings. Likely include these in the report.
Read en.wikipedia.org
ChatGPT
. I'm considering how Wikipedia might be useful for citing specific details about nociceptors discovered in the leech later.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I'm crafting a narrative review to argue pain as a foundational feeling, addressing evidence and criticisms, and ensuring a balanced evaluation.
Read from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfRead from Pain - Origins, Evolution and Link to Emotions (PhD Thesis).pdfChatGPT
I'm looking at SciAm [52†L25-L33] and the IASP definition [53†L495-L503] to highlight pain's ubiquity and sensory-emotional elements.
