Chapman & Huffman suggest that we might change people’s behavior toward animals by resisting an argument that because humans are intellectually superior to animals, they are also morally superior to animals. C & H try to show that the premise is false: Humans are not intellectually superior. Several commentators have resisted this response. We suggest that there are other ways of attacking the argument: The notion of moral superiority on which the argument relies is dubious, and the obvious ways of reformulating the argument are instances of the “naturalistic fallacy.”

Chapman & Huffman argue that we should not consider humans as unique and superior to nonhuman animals. Ecofeminism advocates the respectful treatment of humans, nonhuman animals, and the environment.

Treves et al. (2019) argue that individual organisms should be protected by the courts. This already happens in many countries for rare and endangered species and for symbolically important species (e.g., raptors, songbirds, and bats in the U.S.), and through the international treaty for whales. But protection of these individuals stems from a focus on preserving their populations, whereas hunting of individuals is still a culturally accepted practice. Killing of individuals should be limited to valid reasons (e.g., eating the meat) and covered by fair-chase and humane-killing laws (which is not always the case). But “futurity” will not inherit present-day individuals. What we owe them are healthy populations and species, and functioning, diverse biotic systems. Conservation biology is already rightly focused on this holistic view. Finally, empowerment of women and reform of economic systems will do more to stem the loss of biodiversity than adjudication beyond that already in service of protecting vulnerable species.

Integrating physiological and behavioural arousal with social context is fundamental to understanding affect in dogs. Cook et al. (2018) have made a worthy start towards illuminating the neural basis of dog affect underlying resource loss. However, their study depends on retrospective behaviour reports versus direct testing, and an interpretation of differential neural activation that is based on too few dogs. Research groups conducting canine brain-imaging work might: (1) consider collaborative approaches to augment sample sizes and replicability, and (2) take a recent lesson from dog behavioural research regarding a more cautious approach to applying functional labels to physiological and/or behavioural arousal.

Affective variation from euphoria to dysphoria, best understood in humans, is also found in the behavior and neurochemistry of many other mammals. Suicide in humans typically occurs in highly dysphoric and despondent individuals. Self-injurious behavior has been observed in dysphoric and despondent nonhuman primates. In humans, suicide is facilitated by a highly-evolved neocortex giving rise to behavioral flexibility and culture. As Peña-Guzmán indicates, some other mammals also have elaborate neocortices and the capacity for cognitive insight, particularly apes, delphinids, and whales. Suicide is most likely to occur in species where individuals live in stable groups of highly interdependent kin.

Peña-Guzmán (2017) argues that empirical evidence and evolutionary theory compel us to treat the phenomenon of suicide as continuous in the animal kingdom. He defends a "continuist" account in which suicide is a multiply-realizable phenomenon characterized by self-injurious and self-annihilative behaviors. This view is problematic for several reasons. First, it appears to mischaracterize the Darwinian view that mind is continuous in nature. Second, by focusing only on surface-level features of behavior, it groups causally and etiologically disparate phenomena under a single conceptual umbrella, thereby reducing the account's explanatory power. Third, it obscures existing analyses of suicide in biomedical ethics and animal welfare literatures. A more promising naturalistic approach might seek a theoretical understanding of the social/ecological circumstances that drive humans and perhaps other animals to self-destruction.

Sentience is essential to most definitions of pain, including a detailed definition invoked by Sneddon et al. to argue that adult and perhaps larval fish feel pain. Because proving painful sentience in non-human animals is not feasible, multiple lines of indirect evidence are needed to implicate pain. This commentary examines the list of 17 criteria used by Sneddon et al. to conclude that fish have conscious pain. The criteria include tests of nociceptive, motivational, and cognitive properties useful for revealing pain-like states that can be understood biologically and be related evolutionarily to human pain. However, additional research is needed to define the crucial aversive component of pain-like states in fish.

Peña-Guzmán’s discussion of suicide in nonhuman animals has broad implications. In this commentary, I focus on the logical relation between suicide and intention. Proximate cause must be distinguished from ultimate function in explanations of suicide. I briefly discuss two adaptationist accounts of suicidal behavior.

Cook and colleagues (2018) use a novel approach to test jealousy in dogs. Although such a non-invasive approach is more than welcome in comparative research, several methodological shortcomings limit the impact of this study. We briefly outline two main problems. (1) There is no evidence that the fake dogs in the study were perceived as real, and thus as social rivals, which would be a prerequisite for jealousy. (2) It is questionable whether dogs generally show the cognitive prerequisites for jealousy, such as attentiveness toward a social rival, the ability to understand intentions, and a sense of fairness. We suggest that future studies should combine the same creativity with more controlled procedures in order to better understand the evolutionary origins of jealousy.

Domestic dogs are highly social and have been shown to be sensitive not only to the actions of humans and other dogs but to the interactions between them. We used the C-BARQ scale to estimate dogs’ aggressiveness, and we used noninvasive brain imaging (fMRI) to measure activity in their amygdala (an area involved in aggression). More aggressive dogs had more amygdala activation data while watching their caregiver give food to a realistic fake dog than when they put the food in a bucket. This may have some similarity to human jealousy, adding to a growing body of evidence that differences in specific brain activities correlate with differences in canine temperament. The amygdala response habituates when an interaction is observed repeatedly, suggesting that repeated exposures may be a useful behavioral intervention with potentially aggressive dogs.