Does pain scale with mammal mass?

Does pain scale with mammal mass?

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Some biological features scale with the animal mass (see previous Q&A).

Assuming the same concentration of nociceptors on the skin surface, I'm wondering how painful a 1 cm wound will be perceived in mouse, human or elephant. Despite the same firing number of nociceptors, will the mouse feel more pain as a bigger percentage of the body has been injured? Is it known whether pain sensing follows allometric rules?

Does pain scale with mammal mass? - Biology

When one arrives at biology from its sister disciplines of physics or engineering there is a strong temptation to search for consistent quantitative trends and general rules. One such pursuit centers on the power consumption of different organisms, the so-called metabolic energy consumption rate. This example illustrates how scaling arguments work. For many inanimate systems the energy produced has to be removed through the bounding surface area, and each unit of area allows a constant energy flux. The scaling of surface area, A, with the radius, R, goes as A

R 2 . At the same time the volume, V, scales as R 3 . Assuming constant density this will also be the scaling of the total mass, M. The surface area thus scales as A

M 2/3 . How should the energy production per unit mass, B/M, scale? According to our assumption above, the energy is removed through the surface at a constant rate, and thus the total energy produced should be proportional to A, i.e. B

A. Dividing both sides by M and plugging in the scaling of A with M we finally get B/M

M -1/3 . Does this simple scaling result based on simple considerations of energy transfer also hold for biological systems?

The resting energy demand of organisms has recently been compared among more than 3000 different organisms spanning over 20 orders of magnitude in mass (!) and of all forms of life. In contrast to the Kleiber law prediction, this recent work found a relatively small range of variation with the vast majority of organisms having power requirements lying between 0.3-9 W/kg wet weight as shown in Figure 2. Our naïve estimate for a human of 1 W/kg wet weight is somewhere in the middle of this, but the surprising observation is that this range is claimed to also hold for minute bacteria, plant leaves and across the many diverse branches of the tree of life all the way to elephants. Is this again an indication of Monod’s adage that what is true for E. coli is true for the elephant? Further evidence for breaking of Kleiber scaling was provided recently for protists and prokaryotes (J. P. Delong et al., Proc. Natl. Acad. Sci., 107:12941, 2010). Other recent studies stand behind Kleiber’s law and aim to explain it. We are not in a position to comment on who is right in this debate, but we are of the opinion that such a bird’s eye view of the energetics of life, provides a very useful window on the overarching costs of running the cellular economy.

The metabolic rate of an organism is condition dependent, and thus should be strictly defined if one wants to make an honest comparison across organisms. The most extreme example we are aware of is that bees in flight increase their oxygen consumption and thus their energy consumption by about 1000-fold in comparison to resting conditions (BNID 110031). Similarly, humans taking part in the strenuous Tour de France consume close to 10,000 kcal a day, about five times the normal resting value. It is most common to refer to the resting metabolic rate, which operationally means the animal is not especially active but well fed. As the alert reader can imagine, it is not easy to ensure rest for all animals, think of an orca (killer whale) as one example. The values themselves are often calculated from the energy consumption rate that is roughly equal to the energy production rate, or in other cases from the oxygen consumption.

Based on empirical measurements for animals, an observation termed Kleiber’s law suggests a relationship between the resting metabolic energy requirement per unit mass (B/M) and the total body mass (M) that scales as M -1/4 . A famous illustration representing this relationship is shown in Figure 1. Similar to the scaling based on surface area and energy transfer described above, the Kleiber law suggests that heavier animals require less energy per unit mass, but with the value of the scaling exponent being slightly different from the value of -1/3 hypothesized above. The difference between -0.33 and -0.25 is not large but the law suggests that the data is accurate enough to make such distinctions. Over the years, several models have been put forward to rationalize why the scaling is different from that expected based on surface area. Most prominent are models that discuss the rate of energy supply in hierarchical networks, such as blood vessels in our body, which supply the oxygen required for energy production in respiration. To give a sense of what this scaling would predict, in moving from a human of 100 kg consuming 100 W, i.e. 1 W/kg, to a mouse of 10 g (4 orders of magnitude), would entail an increase of (10 -4 ) -1/4 =10 fold, i.e. to 10 W/kg. Jumping as far as a bacterium of mass 10 -15 kg is 17 orders of magnitude away from a human which would entail (10 -17 ) -1/4

10 4 fold increase or 10,000 W/kg. This is 1-3 orders of magnitude higher than the values discussed in the closely related and complementary vignette on “What is the power consumption of a cell?”. But as can be appreciated in Figure 1, the curve that refers to unicellular organisms is displaced in comparison to the curves depicting mammals by about that amount.

Figure 2: Histograms of resting metabolic rates normalized to wet weight. Across many orders of magnitudes of body size and widely differing phylogenetic groups the rates are very similar at about 0.3-9 W/kg wet weight. (Adapted from A. M. Makarieva, Proc. Nat. Acad. Sci., 105:16994, 2008.)

The resting energy demand of organisms has recently been compared among more than 3000 different organisms spanning over 20 orders of magnitude in mass (!) and of all forms of life. In contrast to the Kleiber law prediction, this recent work found a relatively small range of variation with the vast majority of organisms having power requirements lying between 0.3-9 W/kg wet weight as shown in Figure 2. Our naïve estimate for a human of 1 W/kg wet weight is somewhere in the middle of this, but the surprising observation is that this range is claimed to also hold for minute bacteria, plant leaves and across the many diverse branches of the tree of life all the way to elephants. Is this again an indication of Monod’s adage that what is true for E. coli is true for the elephant? Further evidence for breaking of Kleiber scaling was provided recently for protists and prokaryotes (J. P. Delong et al., Proc. Natl. Acad. Sci., 107:12941, 2010). Other recent studies stand behind Kleiber’s law and aim to explain it.

We are not in a position to comment on who is right in this debate, but we are of the opinion that such a bird’s eye view of the energetics of life, provides a very useful window on the overarching costs of running the cellular economy.


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The study was approved by the Ethical Committee for the Use of Animals in Research of the School of Veterinary Medicine and Animal Science, Unesp, Botucatu, Brazil, under protocol number 102/2014 and follows the Brazilian Federal legislation of CONCEA (National Council for the Control of Animal Experimentation). This is a prospective, randomized, and blind study conducted at the University farms of the authors´ institutions.

Inclusion criteria were based on clinical examination and laboratorial assessment (haemogram and serum biochemistry—plasma urea, creatinine, alkaline phosphatase, and glutamic pyruvic transaminase) to guarantee they were healthy. Pigs that were not clinically healthy or did not present normal laboratorial data were excluded. Pigs that presented any postoperative complications, clinical problems, such as diarrhoea, or were bruised due to fights during the 24 hours of assessment were excluded.

Pigs were selected from the University commercial production. A pilot study was carried out with 12 piglets aged 35 days, submitted to castration only to define the experimental protocol and to recognize pain-related behaviours. For the main study, 45 Landrace, Large White, Duroc, and Hampshire male pigs were randomly selected. The pigs were aged 38±3 days (range 35–41 days) and weighed 11.06 ± 2.28 kg. Groups of five pigs were allocated in suspended collective iron pens 15 days prior to the surgical procedure for adaptation to the personnel and environment. The pens measured 2.40 x 1.50 x 1.50 meters (length x width x height), and were located side by side, separated by bars. The piglets received commercial feed three times a day and water was available ad libitum in nipple drinkers.

Familiarity with the in-person researcher started during the maternity period when piglets were 14 days old. After a week of contact with the piglets, by cleaning the pen and providing food, the in-person researcher initiated direct friendly contact inside the stall, for 15 minutes three times a day, without making any sudden movement, or using vocal communication, so that the piglets could spontaneously approach.

After the adaptation period, procedures were performed between 8 and 10 AM. The pigs were physically restrained and after local antisepsis, they were submitted to bilateral local anaesthesia with 0.5 mL of 1% lidocaine without vasoconstrictor (Xylestesin ® , Cristália, Itapira, São Paulo, Brazil) injected subcutaneously at each incision line, parallel to the scrotum shaft, followed by 1 mL injected intratesticularly at each testicle. After five minutes, orchiectomy was performed by the same surgeon. Four hours after the surgical procedure, the in-person researcher injected analgesic rescue with 2 mg/kg of flunixin meglumine (Flunixin ® , Chemitec, São Paulo, Brazil) and 0.5 mg/kg of morphine (Dimorf ® , Cristália, Itapira, São Paulo, Brazil) intramuscularly (IM) in the cervical region. At the end of the observation period of 24 hours, the animals received 2 mg/kg of flunixin meglumine IM, once a day for two consecutive days. The in-person researcher treated the surgical wounds topically with silver sulfadiazine (Bactrovet ® , König, São Paulo, São Paulo, Brazil), once a day for five days and assessed the surgical wound every 48 hours thereafter, for 10 days.

The pigs were evaluated from 24 hours to 16 hours before surgery and at 2, 4, 6, 8, and 24 hours after castration. Cameras were positioned on the ceiling of the pens to record 30-minute recordings at each of these moments, for a total of 135 hours. The pigs had no visual contact with the in-person researcher. After video recording, if the food was not available at the feeder, the researcher provided a small amount of food, and a short period of video was recorded to evaluate appetite. After the end of the field study pigs were kept until 145 days of age when they were submitted to humane slaughter accomplished by electrical stunning, followed by exsanguination, according to the Brazilian Federal legislation (Ministry of Agriculture).

The videos from the main study were observed for the first time for recognition of different behaviours and elaboration of an ethogram, based on previous studies [6,8,32–34]. After this first analysis, four moments were selected as the most representative as described in Fig 1. The footage corresponding to each of these moments was observed again to measure the duration and frequency of each pain-related behaviour.

The scale was developed according to the analysis of the relevance of pain-related behaviours previously described in the literature [6,8,32–35] and behaviours observed both in the pilot study and during video edition by the in-person researcher.

Once the initial proposed scale had been defined, content validity was assessed by three evaluators experienced in assessing pain in other domestic species, who scored each behaviour according to the degree of importance related to pain (-1 = irrelevant item 0 = do not know 1 = relevant item). Items which reached an average score ≥ 0.5 were included in the scale [21,22,36] From this point the scale was considered ready for video analysis. The proposed scale was composed of six behavioural items. Each item presented four descriptive levels. A numerical score was attributed from 0 to 3, where “0” reflected normal animal state (free of pain) and “3”, the maximum value, corresponded to accentuated behavioural alteration. The maximum score of the entire scale was 18 points.

The in-person researcher edited each of the four 30-minute videos into 4-minute videos representing the 4 moments previously described (Fig 1). The 180 edited videos were analysed by four observers, two men (SPLL and PINN) and two women (FAO and ALA). The first two are the senior authors, with above 20-year experience in anaesthesia and pain assessment in farm animals. FAO developed the cattle postoperative pain scale [22] and ALA was considered the “gold-standard” as she was the in-person researcher responsible for video recording and editing as well as creation of the ethogram. All observers watched the videos in a random order, without knowledge about the moment they were observing (blind analysis).

After watching each video, the observers, based on their clinical experience, initially stated if they would provide rescue analgesia at that moment or not. Subsequently, they were required to ascribe a score for the visual analogue scale (VAS), numerical rating scale (NRS 0 “no pain” to 10 “worst possible pain”), the simple descriptive scale (SDS 0—no pain to 3—intense pain) and UPAPS. After one month, each observer blindly analysed the footage again with a new order of moments and pigs, to establish the intra-observer reliability.

Statistical analysis

For the ethogram analysis the time spent in minutes and the percentage of each behaviour before and after surgery were compared by the Friedman test. Differences were considered significant when p < 0.05.

Validation of the pain scale was processed as described before [21,37]. The intra- and inter-observer reliability were assessed by comparing the data between the first and second analysis for each observer and by comparing the degree of agreement among different observers respectively. To define, for the sum of the scores, the inter-and intra-observer reliability, the intra-class correlation coefficient (ICC) was used. ICC = 1 indicates high reliability (no error), whereas ICC = 0 indicates no reliability. The 95% confidence interval (CI) was calculated for each ICC value with 95% CI [22] at all moments assembled. The weighted kappa coefficient was used to calculate the correlation of each item of the scale among the observers, encompassing all moments of assessment. The values obtained were interpreted by Altman’s classification as: 0.81–1.0 very good 0.61–0.8 good 0.41–0.6 moderate 0.21–0.4 reasonable and <0.2 poor [38].

The criterion validity was analysed by concurrent and predictive validity. Concurrent validity was investigated by comparing the scores obtained by the proposed scale against those determined by VAS, NRS, and SDS [21,22,39]. The interpretation of the Spearman’s correlation coefficient was defined by the calculation of the results of each observer, as well as for all observers together. A second method to measure concurrent criterion validity was by assessing the agreement between the gold-standard assessor and the other observers. The weighted kappa coefficient was calculated with a CI of 95% [40] for each item of the scale, encompassing all assessment moments. For the total score of UPAPS, the intraclass correlation coefficient (ICC) type "consistency" was used, and its 95% CI. The results of the kappa coefficient and ICC were interpreted [37] according to Altman’s classification [38].

Predictive criterion validity was evaluated by the number of pigs that should receive rescue analgesia consistent with the Youden Index (described below) at first moment after surgery when pigs should express the most intense pain (M2). Fisher´s exact test was used to compare the indications of rescue analgesia based on the Youden index vs clinical experience.

Principal component analysis defined the number of factors (dimensions or domains) determined by different variables and establish the extension of the scale [37,41,42]. The appreciation of the main components subsidized the execution of the principal component analysis and the factors were based on Kaiser’s criterion, which indicates maintenance of all components with eigenvalues > 1 [43]. The factorial structure was confirmed when items showed a factor load ≥ 0.50 or ≤ -0.50.

Item-total correlation based on the Spearman coefficient was performed to assess homogeneity and relevance of each item of the scale. Each item was correlated with the sum of all scale items, excluding that item, to avoid inflating the results. Values between 0.3 and 0.7 were accepted [23].

The internal consistency of the scale, to determine the interrelation among the items in the instrument, was assessed by calculation of Cronbach’s alpha coefficient [44]. Values were considered as follows: 0.60–0.64, minimally acceptable 0.65–0.69, acceptable 0.70–0.74, good 0.75–0.80, very good and > 0.80, excellent [45].

Construct validity was determined by the hypothesis test methodology. The first hypothesis is that if the scale truly measures pain, the scoring after surgery should be higher than the preoperative score (M1 versus M2). The second and third hypotheses are that the score should decrease after analgesia and over time (M2 versus M3 and M2 versus M4, respectively). The values were expressed in medians and significance was analysed by the Friedman’s test [21,22]. According to this analysis, it was possible to assess the response capacity (responsiveness) of the scale.

Specificity was assessed at M1, considering that the piglets were free of pain and reflected the true negative results. The scores at M1 were transformed into dichotomous items and entered into the equation: Specificity = TN/TN+FP, where TN = number of true negatives (score 0, indicating that piglets were not expressing pain) FP = false positives (scores 1, 2, or 3, indicating that piglets were expressing pain before surgery, when they should be supposedly pain-free). Sensitivity was calculated at M2, considering that this was the time pain would be the greatest and reflect the true positive results. Likewise for specificity, scores at M2 were transformed into dichotomous variables and the following equation applied: Sensitivity = TP/TP+FN, where TP = true positives (scores 1, 2, or 3, indicating that piglets were expressing pain after surgery, as expected), FN = false negatives (score 0, indicating that piglets were not expressing pain, when they should be expressing pain after surgery). Specificity and sensitivity were considered excellent when 95–100% good when 85–94.9% moderate when 70–84.9% and not-specific or not-sensitive when <70% [29].

The frequency distribution of the presence of scores 0, 1, 2, and 3 of each item at each moment was assessed by descriptive statistical analysis according to the 2nd phase of the gold standard video analysis.

The data relative to the indication of rescue analgesia were used to determine the optimal cut-off point, that is, the minimum score suggestive of the need for analgesic rescue or intervention. This determination was based on the Youden index, which determines the highest sensitivity and specificity value concurrently from the Receiver Operating Characteristic (ROC) curve [21,22], providing a graphic image of the relation between the “true positives” (sensitivity) and the “false positives” (specificity). The discriminatory capacity of the test was determined by the area under the curve (AUC) [46,47]. AUC values above 0.9 represent high precision. In addition, the diagnostic uncertainty zone was determined by two methods [48,49]: 1) calculating the 95% confidence interval (CI) by replicating the original ROC curve 1000 times according to the bootstrap method and 2) calculating the sensitivity and specificity value > 0 90. The lowest and highest values of these two methods among all evaluators was assumed to be the diagnostic uncertainty zone [50].

For determination of pain, intensity scores of the 2nd phase from all observers were classified as no pain, mild, moderate or intense pain, at the time of most intense pain (M2). Non-hierarchical cluster analysis was performed, applying the “maximum” distance and the “Ward.D2“ method using the total score of UPAPS and NS [51], followed by the Kruskal-Wallis test to assess the difference between the groups.

Statistical analysis was performed using R software in the Rstudio integrated development environment (Version 1.0.143—©2009–2016, Rstudio, Inc.). Differences were considered significant when p <0.05.

Analytical balances have finer readability, are much more sensitive to changes, and can detect smaller variations in mass than toploading balances. Semi-micro and microbalances are part of this category with much smaller capacities and higher resolutions.

Moisture balances measure the amount of liquid in a substance and are often used in food testing. They weigh the existing item or product, apply heat to evaporate any moisture, and re-weigh to provide the data used to calculate the moisture content.

Sodium channels and mechanisms of neuropathic pain

Na+ channels are large transmembrane proteins with a voltage-gated central pore capable of selectively passing Na+ ions. They are critical determinants of the electrical excitability of sensory neurons and play a key role in pain sensation by controlling afferent impulse discharge. Injury and disease affecting peripheral nerves induces axonopathy and demyelination. These neuropathic changes, in turn, trigger membrane remodeling in injured afferents and perhaps also in uninjured neighbors. A major consequence of the remodeling is increased cellular excitability. This is due in large part to subtype-selective abnormalities in the expression and trafficking of Na+ channels and perhaps also to altered kinetic properties of unitary channels. Hyperexcitable neurons show enhanced membrane resonance, rhythmogenesis, and ectopic spiking. The resulting excess discharge constitutes a primary neuropathic pain signal. In addition, it triggers and maintains central sensitization. This amplifies residual afferent input, yielding tactile allodynia, and it also amplifies ongoing ectopia that exaggerates spontaneous pain. Membrane-stabilizing Na+ channel ligands suppress neuropathic pain by selectively reducing membrane resonance in injured afferents and hence ectopic hyperexcitability. The clinical usefulness of these peripherally acting drugs might be enhanced by reducing their central side effects.

Perspective: Neuropathic pain is a complex outcome of multiple pathophysiological changes that develop in the peripheral nervous system (PNS) and the central nervous system (CNS) following nerve injury or disease. All or most of the CNS changes are thought to be due to abnormal signaling from the PNS, notably electrical hyperexcitability of peripheral sensory neurons. Because hyperexcitability is associated with abnormal sodium channel regulation, this process is a prime target for therapeutic intervention.

Animals as Persons: Can We Scale Intelligence or Sentience?

A recent essay by Aviva Rutkin called "When is an animal a person? Neuroscience tries to set the rules" focuses on the daunting question, "When is an animal a person?" It's surely an extremely important question and also a "hot" topic, as many people are working on achieving the legal status of "person" for nonhuman animals (animals). For example, attorney Steven Wise and people working with The Nonhuman Rights Project have been working to achieve legal personhood for chimpanzees, and a recent essay by philosopher Mark Rowlands called "Are animals persons?" concludes "personhood is widely distributed through the animal kingdom." More information on the general topic of personhood in other animals can be found here.

Almost human?

The title of Ms. Ritkin's print essay is "Almost human?" and when I saw it I immediately thought about whether it's really possible to scale intelligence or sentience and make comparisons among individuals of different species. Her essay is currently unavailable online, so here are a few snippets to whet your appetite for more.

Concerning Steven Wise's efforts, Ms. Ritkin writes,

. the non-profit Nonhuman Rights Project has drawn attention for its attempts to take legal action to free captive chimps – so far Hercules and Leo from a Long Island research lab and Kiko and Tommy from private ownership. A new documentary, Unlocking the Cage, chronicles the group’s so-far-unsuccessful quest for what its president Stephen Wise describes as 'legal transubstantiation'. If the courts ever find in its favour, 'the non-human animal would come out of that courtroom looking the exact same, but her legal status would be forever changed', Wise said on the film.

Public opinion does seem to be shifting toward giving animals at least some rights. Last year, a Gallup poll found that 32 per cent of people in the US believe that animals should receive the same rights as people – an eight-point rise since 2008.

But what rights might those be? The Nonhuman Rights Project focuses on habeas corpus, to protect against unlawful imprisonment. The group wants captive chimps to be sent to a sanctuary, where they can live in a wilder and more open environment. So far, no judge has ruled in favour of their cause. However, in May, it was announced that the chimp research facility where Hercules and Leo live will transfer the pair, along with the 200 others, to a sanctuary.

A checklist for personhood

A most important aspect of Ms. Ritkin's essay is her inclusion of a checklist for personhood. She writes:

Philosophers disagree on exactly what it would take for an animal to qualify as a person. Kristin Andrews at York University in Toronto, Canada, suggests searching for the six attributes listed here.


Showing emotion, perspective and a point of view. Chimps and bonobos throw tantrums when they don’t get their way. One researcher has reported a baboon urinating on a rival as a form of revenge.


The ability to think and reason logically. Elephants, monkeys, birds and even fish have shown some understanding of basic maths. Some animals can handle tougher problems: in one study, orangutans worked out the principles of water displacement to get a peanut. Many animals have also mastered tools: chimpanzees use leaves as toilet paper, for example, and crows make their own hooked tools to forage.


A distinctive, individual character. Individual squid can be shy or bold sharks may be more social or solitary and some great tits act cautiously while others are the reverse. Members of some spider species can vary in how docile or aggressive they are. As for chimps, their personalities can be assigned to sit on a six-point scale.


The capacity to form bonds with other creatures, and to care for others and be cared for. Pilot whales stay close to one another as they dive, and use frequent bodily contact, behaviour that looks like it is giving social comfort. Monkeys and elephants grieve the loss of fellow creatures. Imitation, too, could be a sign of the ability to form relationships – newborn chimps can imitate facial expressions, for example.

Narrative self

The sense of having an autobiographically connected past and future. Dolphins can remember tricks they did in the past. Apes have some ability to look forward and backward: by remembering major events from previously watched movies, or taking a tool with them to solve a human-posed puzzle.


The ability to make decisions for oneself. Communication might indicate an animal’s preference – like when an orangutan was observed pantomiming for help with a coconut. Some species also show signs of distinct social cultures orcas, for example, live in groups with their own lifestyle, social structure and hunting techniques."

Can we truly scale intelligence among species and should intelligence be the defining measure for granting personhood?

" . the question is not, Can they reason? nor, Can they talk? but, Can they suffer? (Jeremy Bentham)

Two sentences that caught my eye in Ms. Ritkin's essay are: "Instead of giving animals the full upgrade, we could start to understand them as near-persons, or at least as creatures of heightened moral value. We could then bestow rights in proportion to their abilities and intelligence." (my emphasis)

It's clear that humans will be the standard against which other animals will be compared and to which animals will be "upgraded," and I don't see how this exercise will really clear up the matters at hand. And, two questions immediately came to mind, namely, "What is a near-person?" and "What about humans who are near-persons?" I'm not going to ponder these questions here, and I know they have been discussed by philosophers and lawyers with varying points of view.

How does sentience factor in to assessments of personhood? One important point concerns the concentration on intelligence, or sapience, but many people really are concerned with an individual's capacity to experience different emotions, or sentience. Often, when people are concerned with an individual's well-being, they focus on their ability to experience pain. Like Jeremy Bentham and others, I favor using sentience as the guide for granting personhood. However, quite frankly, I have no idea of how sentience or the ability to feel pain can be reliably scaled among individuals of the same or different species.

The difficulties of cross-species comparisons of intelligence and sentience

I consider questions of scale, or of proportion, about intelligence and sentience in two previous essays. In "Are Pigs as Smart as Dogs and Does It Really Matter?" I wrote, "I don’t consider questions comparing the intelligence of different species to be useful because individuals do what they need do to be card-carrying members of their species. Comparing members of the same species might be useful in terms of the ways in which individuals learn social skills or the speed of learning different task, but comparing dogs to cats or dogs to pigs says little of importance." Many researchers agree that cross-species comparisons of intelligence are fraught with error and species are difficult to accurately rank.

In another essay titled "Do 'Smarter' Dogs Really Suffer More than 'Dumber' Mice?" I considered problems in reliably scaling sentience and the possible relationship between intelligence and sentience. I stressed that there is no evidence that supposedly smarter animals suffer more than animals who supposedly are not as intelligent. In this essay I also wrote, "It's also become clear that the word 'intelligence' needs to be considered in light of what an individual needs to do to be a card-carrying member of his or her species and that comparisons between species don't really tell us much. So, asking if a dog is smarter than a cat or a cat is smarter than a mouse doesn't result in answers that are very meaningful. Likewise, asking if dogs suffer more than mice ignores who these animals are and what they have to do to survive and thrive in their own worlds, not in ours or those of other animals."

Individual pain matters

In "Do 'Smarter' Dogs Really Suffer More than 'Dumber' Mice?" I also wrote, "we need to take the pain and suffering of 'less intelligent' animals very seriously and that speciesist arguments about 'higher' and 'lower' animals need to be shelved. I also stressed "The pains of supposedly 'smarter' animals are not morally more significant than the pains of 'dumber beings.' Solid science supports these ideas and I stand by this conclusion." Three years later, I still do.

Along these lines, Dr. Lori Marino, founder of the Kimmela Center for Animal Advocacy, Inc., says it well: "The point is not to rank these animals but to re-educate people about who they are. They are very sophisticated animals."

It's difficult enough for humans to accurately scale pain among humans, and it's more difficult and arrogant to assume we can scale pain for other animals. My pain is my pain, your pain is your pain, dogs' pain is their pain, and mice's pain is their pain. Ranking other individuals of other species in comparison to humans or to other animals, including members of their own species, robs them of their individuality, and also can be all too self-serving for us.

I wish all of the dedicated people working on personhood for nonhuman animals the best of luck. Even when there are failures, these efforts call attention to the fascinating animals with whom we share our magnificent planet. When essays such as Ms. Ritkin's are read by people who have never even imagined that others are working on these sorts of projects, or by people who want to learn more about what is being done, we can only hope they will get on board and support these efforts.


There is a belief in some scientific and lay communities that because fish respond behaviourally to noxious stimuli, then ipso facto, fish feel pain. Sneddon (2011) clearly articulates the logic by stating: “to explore the possibility of pain perception in nonhumans we use indirect measures similar to those used for human infants who cannot convey whether they are in pain. We measure physiological responses (e.g., cardiovascular) and behavioral changes (e.g. withdrawal) to assess whether a tissue-damaging event is painful to an animal”. In some cases, the inference that fish have affective states arises because of conflation of nociception with pain (Demski 2013 Kittilsen 2013 Malafoglia et al. 2013). Interestingly, sometimes the difference between nociception and pain is recognized but it is still considered safer to err on the side of caution and accept that fish feel pain (Jones 2013). Unfortunately, endowing fish with the subjective ability to experience pain is typically undertaken without reference to its neurophysiological bases (Rose 2002, 2007 Browman and Skiftesvik 2011).

Before interrogating the issue of fish feeling pain and its implications for phenomenal consciousness, I will briefly define several key terms. When I refer to fish it is with the knowledge that this is a highly diverse paraphyletic group consisting of

30,000 species. Since most of the behavioural and neuroanatomical investigations discussed here have been undertaken only on a small number of ray-finned fish, there is considerable extrapolation involved when I use the generic term fish. A noxious stimulus is one that is considered to be physically harmful to an animal without reference to feelings. For example, excessive heat, a skin incision, toxic chemical exposure and extreme mechanical pressure are all stimuli that can perturb normal tissue morphology, and are hence considered to be noxious. Nociception is referred to as the neurobiological processes associated with the activation of peripheral sensory neurons and their upstream neural pathways by noxious stimuli in the absence of conscious feeling. In contrast, pain is the subjective experience of feeling a noxious stimulus (however, in certain central neuropathies in humans it can arise without external stimuli). The subjective “feeling” associated with a sensory stimulus is also referred to as a “quale” or “phenomenal consciousness” (Kanai and Tsuchiya 2012). Given the above, I acknowledge the tautology in the manuscript’s title since the word “pain” is already defined as “to feel a noxious stimuli”. However, the phrase “feel pain” within the title was chosen to over-emphasize the subjective or qualitative nature of pain.

One of the main proponents in the literature of the thesis that fish do not feel pain has been John D. Rose. In a series of comprehensive articles (Rose 2002, 2007 Rose et al. 2014) it was argued that fish do not experience the sensation of pain. Anthropomorphism was considered as a hindrance to understanding the underlying causes of behavioural responses of animals to sensory stimuli (Rose 2002, 2007). Rose advocated attention to the evolution, development and organization of the nervous system in order to understand fish behaviour. He initially drew attention to three key issues (Rose 2002). First, behavioural responses to sensory stimuli must be distinguished from psychological experiences. Second, the cerebral cortex in humans is fundamental for the awareness of sensory stimuli. Third, fish lack a cerebral cortex or its homologue and hence cannot experience pain or fear. In 2007, Rose highlighted the problems of anthropomorphic thinking in respect to fish behaviour and how it influenced welfare issues. He stressed that pain and emotion were not primitive feelings that arose early in vertebrate evolution but were rather more recent acquisitions, associated with the emergence of the cerebral cortex (Rose 2007). In 2014, Rose et al. (2014) rebutted experimental evidence supposedly supporting claims that fish feel pain. They demonstrated deficiencies in methodological approaches and highlighted problems in concluding pain experience from behavioural responses. Moreover, they recognized that teleosts typically lack nociceptors responsible for transmission of pain but instead have an abundance of A-delta fibres that are most likely subserving escape and avoidance responses rather than the experience of pain.

Despite the work of Rose et al. (Rose 2002, 2007 Rose et al. 2014) there remains a strong trend in the literature to bestow fish with the ability to feel pain and to experience fear and other emotions. The alternate view that fish do not feel pain or experience affective states needs more careful consideration, particularly as it has consequences for understanding the neuroanatomical basis of phenomenal consciousness. Here I consolidate the arguments for why fish are believed to feel pain into six main reasons. By undertaking a deeper analysis of the behavioural observations in the light of our understanding of neurophysiology and neuroanatomy, I subsequently propose that it is more plausible and probable to reason that fish do not feel pain. Concluding that fish do not feel pain affords an opportunity to define the basic architectural properties of the neural circuitry necessary for phenomenal consciousness through comparisons of fish and mammalian neuroanatomies. These properties then provide a simple tool for assessing the likelihood that a vertebrate animal will experience “feelings” such as pain.

Take this fifty foot woman as an example. Her puny legs would buckle and collapse under her gigantic mass!

In fact, viewed through the smug nerdy lens of the principle of scale, all sorts of books and movies turn from science fiction to pure fantasy. Here's a thought provoking run-through of the physics behind a lot of movies about shrinking, growing, and other scale-related activities: The Biology of B-Movie Monsters. And here's an essay that includes some analysis of Lilliput.

Alrighty, I've pummelled this topic to death already. Have just returned from a two week holiday, after finishing up at Advantech software. I've been sans-computer for all that time (wrote most of this article on paper using a device known as The Pen, I believe.) Read an interesting book -- freakonomics during the break. (blog here) Recommended.

Watch the video: Tκ Τύπος: Ο πόνος σας, πόνος μας. AlphaNews (August 2022).