Integrating evolution into the study of animal sentience

Animal Sentience

We outline a framework for evaluating scientific evidence of sentience, focusing on pain experience. It includes eight neural and cognitive-behavioural criteria, with confidence levels for each criterion reflecting the reliability and quality of the evidence. We outline the rationale for each criterion and apply our framework to a controversial sentience candidate: decapod crustaceans. We have either high or very high confidence that true crabs (infraorder Brachyura) satisfy five criteria, amounting to strong evidence of sentience. Moreover, we have high confidence that both anomuran crabs (infraorder Anomura) and astacid lobsters/crayfish (infraorder Astacidea) meet three criteria-substantial evidence of sentience. The case is, as yet, weaker for other infraorders, such as penaeid shrimps, highlighting important research gaps. Having demonstrated our framework's application to decapod crustaceans, we hope that future research will apply it to other taxa.

Animal Sentieence

In the target article Crump et al. present 8 criteria to assess whether decapods experience pain. Four of these-sensory integration, motivational trade-offs, flexible selfprotection, and associative learning-could be used to assess sentience in general. In this commentary I discuss difficulties with using these criteria to provide evidence of sentience in decapods, particularly if this evidence is to change public opinion and policies. These difficulties are lack of evidence, the potential to eventually explain the neurobiological basis of the behaviors chosen as criteria, thereby eliminating any explanatory work for sentience, and the reluctance to bring animals that are not cuddly under our moral umbrella.

Animal Sentience

We are in basic agreement with Crump et al. that animal welfare, particularly with regard to the experience of pain, is a topic of importance. However, we come to the issue from a different perspective, one in which all species are sentient and can feel pain. The implications of this theory are discussed.

Animal Sentience

Mikhalevich & Powell make a compelling case that some invertebrates may be sentient and that our moral obligations in the context of welfare should hence extend to them. Although the case is similar to that made for fishes, there is one obvious difference in that examples of invertebrate sentience probably arose independently from vertebrate sentience. We have unequivocal proof that complex cognition arose multiple times over evolutionary history. Given that cognition is our best tool for indirectly quantifying sentience, it seems highly likely that this multiple polygenesis may also have occurred for sentience. In acknowledging this, we must accept that the anthropocentric structure-function arguments that have surfaced in the context of pain are almost certainly too simplistic and cannot account for cases of convergent evolution.

Animal Sentience, 2020

Mikhalevich & Powell (M&P) set up the basic criteria for according moral status equitably, including the capacity for affect. They argue persuasively against assuming that all invertebrates are insentient and hence ineligible for moral consideration. In addition to the relatively clear case of cephalopods, various arthropods may prove to be sentient. We should be aware of various sources of prejudice that M&P discuss and not assume that it would be absurd to attribute sentience and moral status to certain invertebrates.

2019

Animal welfare is an important concern in modern society. The most common ethical underpinning of animal welfare is the concept of sentience. However, there is no agreement yet on the definition of sentience and on which features are essential for a species to be classified as sentient. Unsurprisingly, hot debates flare up periodically about whether a certain species could be considered as sentient and thus on whether its welfare should be granted. In the present paper, we outline the repetitive tendency of such debates, using fish and arthropods as an example. Up to now, these debates tend to end with the vast majority of researchers either recognising sentience in the target species or advising the use of the precautionary principle and thus tentatively act as if the species is sentient in order to take decisions regarding its welfare status. The debate then usually moves to a species progressively less similar to humans and the cycle of the ‘sliding scale’ begins anew. In view of...

Animal minds and animal bodies evolved together. When did consciousness emerge and what animals have it? Consciousness has a distinct structure: a predictive, temporalized stream of intentional content. I argue that this structure also solves the biocomputational problem of controlling a complex, active animal body in space. This problem has been solved three times in animal evolution: in vertebrates, in arthropods, and in cephalopod mollusks. This supports the hypothesis that consciousness itself arose near the root of each of these lineages.

Animal Sentience, 2018

In my target article, I argued that the brains of ray-finned fishes of the teleost subclass (Actinopterygii) are sufficiently complex to support sentience-that these fishes have subjective awareness of interoceptive and exteroceptive sense experience. Extending previous theories centered on the tectum, I focused on the organization of the fish pallium. In this Response to the commentaries, I clarify that I do not propose that the fish pallium is, or must be, homologous to the mammalian neocortex to play a role in sentience. Some form of a functionalist approach to explaining the neural basis of sentience across taxa is probably most appropriate. However, what is known about the neural correlates of consciousness in humans is adequate to provide a starting place for investigation of the correlates of sentience in other animals, including fishes. Ultimately, though, hypotheses and experiments to evaluate anatomical and physiological correlates specific to sentience in fishes will be necessary.

Animal Sentience, 2020

Mikhalevich & Powell provide convincing empirical evidence that at least some invertebrates are sentient and hence should be granted moral status. I agree and argue that functional markers should be the primary indicators of sentience. Neuroanatomical homologies provide only secondary evidence. Consensus regarding the validity of these functional markers will be difficult to achieve. To be effective in practice, functional markers of sentience will have to be tested and accepted species by species to overcome the implicit biases against extending moral status to invertebrates.

Animal Sentience, 2020

Sentience is not confined to animals with large or human-like brains. Moral standing should be accorded to all animals, not just vertebrates: invertebrates deserve moral consideration too. Carefully defining the relevant terms can help clarify the relationship between sentience and welfare. All animals have welfare but humans accord more protection to sentient animals. Humans should be less human-centred.