As a child, Gordon Burghardt, SB’63, PhD’66, tended a menagerie that at different points included turtles, snakes, and lizards as well as a parakeet, a raccoon, and a skunk. He was fascinated by the rich array of wildlife in his hometown of Milwaukee and amazed that so many kinds of animals could thrive there.

Fittingly, he became an ethological psychologist, a scientist who investigates animal behavior. Over his 60-year career, Burghardt, Alumni Distinguished Service Professor in the Department of Psychology and Neuroscience and the Department of Ecology and Evolutionary Biology at the University of Tennessee, Knoxville, has conducted groundbreaking research into the consciousness of animals.

Burghardt has long been fascinated by what he calls the “private experiences” of animals. In his studies, he teased out insights into their emotional lives and even the degree to which they play, an activity once thought to be something only humans did.

When Burghardt was a young professor in the 1970s, he knew he wanted to explore animals’ mental and emotional states. It was a radical decision, influenced in part by his time studying under Eckhard Hess, a UChicago biopsychologist who did foundational work on imprinting—the attachments animals form to the first organisms or objects they see.

When Burghardt was beginning his academic career, many experts believed that “any attribution of mental processes and emotions in animals was anthropomorphic,” he recalls—and a “cardinal sin” in the field at the time.

He attended conferences with researchers who, he says, were doing “cruel, outrageous things” to lab animals and seemed unbothered by “the consequences of what they were doing in terms of the animals’ feelings and sentience.”

His scientific intuition, as well as his compassion, showed up in his research and his relationships with the animals he studied—among them, an iguana named Emma who became his lab’s mascot. “She would tuck her head and want to be scratched just like a cat,” Burghardt recalls. Reptiles “don’t have the kind of vocalizations that mammals do, like whimpering or crying, or facial expressions that would allow us to make the same comparisons with them the way we would with, say, a dog. … But they have almost all the same brain characteristics as mammals, including in the limbic system, involved in emotional responses.”

Over the years his restless scientific imagination increasingly led Burghardt to study whether animals do things for enjoyment. He spent two years at what is now the Smithsonian’s National Zoo and Conservation Biology Institute, giving balls, sticks, and rubber hoops to 60-pound Nile softshell turtles and watching them chew and tug the objects in what seemed like fun ways. Observing a female Komodo dragon at the same zoo, he watched her chomp and shake a sneaker in her jaws, as a dog would.

Burghardt and Harry Greene, a professor of ecology and evolutionary biology at Cornell who earned his PhD under Burghardt, went to Slothia, an islet off Barro Colorado Island in Panama, to learn more about the behavior of newly hatched green iguanas. The young lizards frolicked together instead of each going their own way, as scientists had long presumed. The hatchlings grouped together and even slept atop one another.

“Gordon and I sat in our blind saying, ‘Nobody’s ever seen anything like this before,’” Greene recalls. Science magazine honored their finding by putting it on the cover of a February 1977 issue. Thanks to the pair’s discovery of young iguanas’ social complexity, researchers now believe such behavior speeds their growth and discourages predators.

“From the experimental side, the rigor of his science is excellent, and the design of his experiments is shrewd,” says Stephen S. Hall, author of Slither: How Nature’s Most Maligned Creatures Illuminate Our World (Grand Central Publishing, 2025). “It’s legitimate to think of Burghardt as kind of the philosopher-king of the field.”

Burghardt spent years getting up close and personal with mammals too. In 1970 rangers found two motherless black bear cubs in the Great Smoky Mountains National Park. Burghardt named them Kit and Kate and kept them in his home for several weeks until a suitable enclosure could be built in the park. He then spent four years studying them. Through close, long-term observation, Burghardt and his graduate student Ellis Bacon discovered that black bears see in color and that their up close vision is sharp.

(Not long after, he also fostered a lion cub named Meg for what is today known as Zoo Knoxville. During Meg’s stay, a burglar broke into Burghardt’s home but took nothing—presumably terrified by the sight of a lion bounding down the stairs.)

One of Burghardt’s defining moments came with the 2005 publication of his book The Genesis of Animal Play: Testing the Limits (MIT Press). It had “a revolutionary effect,” according to Sergio Pellis, a play behavior expert and professor of neuroscience at the University of Lethbridge in Canada who has collaborated with Burghardt.

This comprehensive interdisciplinary work documents play in a surprising array of creatures as different as frogs, insects, and sharks. What’s more, Burghardt uses its pages to reveal his five criteria that define play in animals (including humans)—it must be voluntary; unlike other behaviors; repeated; done when the animal is healthy and unstressed (though researchers have since learned animals also play to reduce mental tension); and “not fully functional.” In other words, it appears to be done for amusement and not for survival. This framework has had “an enormous impact on the wealth of comparative data we have now,” says Pellis.

Burghardt also developed the concept of critical anthropomorphism. Some researchers had been criticized for proposing that the causes of animals’ behavior paralleled human experiences. Burghardt contended that scientists are justified in using their own experiences as biological beings to understand animals’ activities, so long as they use their knowledge of other species’ physiology, sensory abilities, and behavior patterns to make scientifically based hypotheses.

He demurs when asked to predict what future research might reveal about animals’ inner worlds. “We are probably never going to know completely, because experiences are very rich. It’s the same thing with humans,” he says. “Will we ever really know what’s going on inside another person?”