Scientific thought on emotions in animals

"As far as we know, this is the first assessment of how animal behavior researchers across a range of disciplines think about emotions and consciousness in non-human animals," says Marcela Benítez, assistant professor of anthropology at Emory University and corresponding author of the paper. "It gives us a snapshot in time so that 20 years from now, we can revisit how scientific experts may have changed their views."

A majority of the survey respondents ascribed emotions to "most" or "all or nearly all" non-human primates (98%), other mammals (89%), birds (78%), octopus, squids and cuttlefish (72%) and fish (53%). And most of the respondents ascribed emotions to at least some members of each taxonomic group of animals considered, including insects (67%) and other invertebrates (71%).

The survey also included questions about the risks in animal behavioral research of anthromorphism (inaccurately projecting human experience onto animals) and anthropodenial (willful blindness to any human characteristics of animals).

"It's surprising that 89% of the respondents thought that anthropodenial was problematic in animal behavioral research, compared to only 49% who thought anthromorphism poses a risk," Benítez says. "That seems like a big shift."

Anthromorphism, she notes, has long been a leading argument against those who attributed feelings to animals.

First author of the current paper is Matthew Zipple, a neurobiologist at Cornell University's Laboratory for Animal Social Evolution and Recognition. Co-authors include Mackenzie Webster, an Emory postdoctoral fellow studying cognition in nonhuman primates, and Caleb Hazelwood, a philosopher at Duke University.

Since ancient times, philosophers have pondered the seemingly simple question of whether animals experience emotions. Aristotle believed that animals and humans share similar emotions while Descartes argued that animals were more like machines, lacking the capacity for emotions or consciousness.

In the mid-1800s, famed naturalist Charles Darwin wrote that "the lower animals, like man, manifestly feel pleasure and pain, happiness and misery." By the mid-20^th-century, however, leading behavioral theorists denigrated the idea of studying animal emotions since, even if they existed, they were scientifically unmeasurable and unverifiable.

The late primatologist Frans de Waal, an Emory emeritus professor of psychology, helped change this dynamic through his groundbreaking studies of animal cognition. From de Waal's 1982 book "Chimpanzee Politics" to 2019's "Mama's Last Hug: Animal Emotions and What they Tell Us about Ourselves," attitudes about whether animals might have thoughts worthy of scientific exploration changed dramatically.

"Frans de Waal definitely helped kick open the door," Benítez says. "He gave a new generation of scientists permission to ask questions about the inner lives of animals."

Benítez' work lies at the intersection of anthropology, psychology and evolutionary biology. She currently studies cooperation and other social behaviors in capuchin monkeys. "A key component of cooperation often involves forming emotional bonds with one another," she says. "So, I can't shy away from considering emotions in my research."

She did a postdoctoral fellowship in the lab of Sarah Brosnan, an Emory PhD graduate and a student of de Waal when he served as director of the Living Links Center for the Advanced Study of Ape and Human Evolution at the Emory National Primate Research Center. Brosnan is now a professor of psychology at Georgia State University where she investigates the evolution of cooperation, decision-making and economic behavior among primates.

Benítez says that the legacy of de Waal was a main reason that drew her to join the faculty at Emory, where she feels that she is walking in his footsteps.

De Waal's popular, bestselling books also shaped public perception of animal minds.

Several of the Emory graduate students now working in Benítez' Social Cognition and Primate Behavior Lab read about de Waal's work when they were younger. "That inspired them to want to study animal cognition," she says. "His legacy is really widespread."

As the field has grown, Benítez and colleagues wanted to quantify animal behavior researchers' perceptions of the taxonomic distribution of animal emotionality. They developed a survey of multiple-choice questions, free-form text fields and rating scales and sent it to leading graduate school programs in animal behavior research across disciplines. They also posted solicitations for the survey on X, aimed at researchers in these fields.

The 100 survey respondents spanned a range of specialties, including behavioral ecologists, evolutionary biologists, neuroscientists, biological anthropologists, cognitive psychologists and biological psychologists. They comprised graduate students (45), faculty (28), postdoctoral fellows (20), retired faculty (2), other PhD researchers (3) and undergraduate students (2).

The most common taxa of animals studied among respondents were birds (43%), non-human primates (32%) and other mammals, though each of the taxa that the survey asked respondents to assess were studied by at least some members of the sample.

The survey defined displays of animal consciousness in its most basic form, meaning that they are aware of their own existence. A majority of respondents ascribed consciousness to a broad taxonomic breadth of animals, although at slightly lower majorities as compared to emotions.

Near the end of the survey, respondents were asked to define emotion.

A little more than half of their definitions referred to emotions as a response to either internal or external stimuli. A majority also referred to emotions being subjective experiences or related to consciousness or mindedness. And 40% of the responses identified emotions as functioning to motivate behaviors.

Only 81 out of the 100 survey respondents provided a definition, perhaps due to the challenge of verbalizing a working description.

"I don't have a clear definition either," Benítez says. "I see emotions as a sort of internal process in responding to external stimuli that has an impact on how a situation is perceived. I go to the most basic definition because that allows us to explore that capacity in non-human primates."

Even in human studies, Benítez adds, it is challenging to determine which biological markers to measure and how to adequately describe and quantify something as complex and variable as emotions. They may include everything from instinctual reactions of disgust or fear to deep feelings of affection and empathy for others.

Animal studies are further complicated by the fact that researchers can't ask an animal how it's feeling.

And while experiments with animals in labs can be tightly controlled, the results may be skewed since the animal is not interacting within its natural environment. Animal behavior experiments in the wild provide valid social and ecological contexts but they are challenging to design and to control.

"I'm trying to bridge that gap," Benítez says. Her work is unique in that she studies behavior in both a captive population of tufted capuchins and of wild white-faced capuchins as co-director of the Capuchins de Taboga Costa Rica project in Liberia, Costa Rica.

Benítez and her collaborators at La Universidad Technica Nacional are beginning to deploy AI techniques, facial recognition software and touch screen computers on presentation platforms in the wild. These tools may help them get at many questions surrounding capuchin monkey behavior, including how they decide whether to cooperate or compete with one another while they are interacting in their natural world.

"We've only scratched the surface of exploring what animals are capable of experiencing," Benítez says. "It's an exciting time as new methods are being developed that may help us better understand how an animal may be feeling and how that links to the decisions that they make."

"As an anthropologist," she adds, "a large part of my desire to understand the interior lives of animals is to better understand our own ancestry. In what ways are we a unique species? Understanding the evolution of emotions is integral to that question."