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Do non-human animals such as cats, dogs, and chimpanzees have emotions like happiness, sadness, fear, and anger? What kind of reasoning is required to justify the judgment that animals have emotions? Here is a dialogue between an advocate of animal emotions and a skeptic.
Advocate: It is obvious that humans are not the only animals that have emotions. Anyone who has ever had a pet cat or dog knows that feeding them and petting them makes them happy, whereas dangers make them afraid and angry.
Skeptic: Not so fast. There is no doubt that such animals can be rewarded and threatened, but their behavior is no guarantee that they are experiencing the emotions that people have.
Advocate: Your skepticism is bizarre. It reminds me of the philosophical problem of other minds, where the skeptic says, "I know that I have a mind, but how can I possibly know that anyone else has a mind?"
Skeptic: The parallel between arguments about other human minds and ones about animal minds is not good because other people are much more similar to you than cats and dogs are. Can you provide a more substantial argument?
Advocate: Gladly. The relevant kind of argument is what philosophers call inference to the best explanation, which is the standard way in science and everyday life of arguing about the existence of something you cannot directly observe. Most scientists believe in atoms because that hypothesis provides the best explanation of many phenomena in chemistry and physics. Similarly, we infer that the best explanation of other people's behavior is that they have minds just like us. Alternative explanations, such as those that suggest other people are robots controlled by space aliens, are utterly implausible. Analogously, the best explanation of the behavior of cats and dogs is that they are experiencing emotions.
Skeptic: But wait, you neglect the fundamental principle of inference to the best explanation that you have to consider alternative hypotheses. For cats and dogs, we can explain their behaviors merely on the basis of reward mechanisms and threat response mechanisms that operate in all animals, including humans. When a cat is purring or a dog is wagging its tail, this response results from neural activity in its reward centers such as the nucleus accumbens. When a cat is yowling or a dog is growling, this results from neural activity in its threat detection centers such as the amygdala. These explanations are much simpler than making the additional assumption that cats and dogs are actually experiencing emotions of happiness and fear. Unlike people, pets cannot tell us that they are happy or anxious.
Advocate: But thanks to neuroscience, we know that all mammal brains are similar with respect to the overall organization. In the argument about other human minds, we not only use the hypothesis that other persons have minds in order to explain the behavior, we know enough about human neuroanatomy to be able to explain that it is because they have brains like ours. We increasingly know the mechanisms by which brains make minds, which operate across humans and other mammals. Admittedly, this argument doesn't apply to insects, reptiles, and fish, which have much simpler brains. Whether it applies to birds is hard to say, because they don't have a prefrontal cortex, although they do share a similar brain structure: the nidopallium caudolaterale.
Skeptic: The analogy between the brains of humans and non-human animals is not as good as you suppose. The brains of humans are far larger than those of cats and dogs, around 86 billion neurons as opposed to less than a billion. In particular, humans have a much larger prefrontal cortex, the area that is used for complex reasoning, so they are much more capable of making complex assessments of situations. If emotions were just physiological responses, then it would be plausible that animal emotions are the same as those in people. But physiology alone is not enough to discriminate between emotions such as fear and anger, which require an appraisal of situations with respect to situations and goals. This limitation is why non-human animals are incapable of complex human emotions such as shame, guilt, and fear of embarrassment.
Advocate: We are not talking about such emotions that depend on complexities of language and culture, but about much more basic emotions such as happiness, sadness, fear, and anger. These do not require a linguistically and culturally mediated appraisal of the situation, merely that an animal can have some nonverbal ways of appreciating whether its goals such as food and safety are being satisfied or threatened. With respect to these, the neuroanatomy of mammals is sufficiently similar to that of humans to provide analogy-based support for the inference that animal emotions are the best explanation for their behavior.
Skeptic: But the analogy remains weak, and you still haven't recognized that the alternative explanations of animal behavior based on reward and threat mechanisms are simpler than the attribution of emotions, making fewer assumptions about mental states. I suspect that your real reason for wanting to believe in animal emotions has nothing to do with inference to the best explanation. It's just a motivated inference: you want to believe that animals have emotions because you want them to feel about you the way that you feel about them. People love their cats and dogs, so they naturally want to be loved back.
Advocate: Even if people have this motivation, it does not undermine the basic logic of the inference. Simplicity is not a standalone criterion for inference to the best explanation but has to be balanced against explanatory breadth. Attributing emotions to animals can explain aspects of their behavior that mere reward and threat mechanisms do not cover.
Skeptic: To make this convincing, you need to specify the kinds of behavior that cannot easily be accounted for by reward and threat mechanisms, and to show that animal brains are capable of the appraisals that contribute to emotions in human brains. Until then, it is better to remain at least undecided about whether animals have emotions.
References
Barrett, L. F. (2017). How emotions are made: The secret life of the brain. Boston: Houghton Mifflin Harcourt.
de Waal, F. B. M. (2017). Are we smart enough to know how smart animals are? New York: Norton.
LeDoux, J. E. (2015). Anxious: Using the brain to understand and treat fear and anxiety. New York: Viking.
Lipton, P. (2004). Inference to the best explanation (2nd ed.). London: Routledge.
Safina, C. (2015). Beyond words: What animals think and feel. London: Macmillan.
Thagard, P. (1989). Explanatory coherence. Behavioral and Brain Sciences, 12, 435-467.
