I have lived for eight years now with my dog, Charlie—a bloodhound who’s embarrassingly bad at tracking scents. He greets me jubilantly every time I come home, even if it’s from a quick grocery run. I can hear his tail go thump-thump-thump on the floor in the next room when I laugh; he echoes my mirth even when he can’t see me.

Yet, despite sharing this bond, I often sit down next to him on the couch, give him a hug, and ask my wife, “Do you think he loves me?” “Yes, yes!” she replies, with only slight exasperation, which is charitable because I ask so often.

This routine is almost like a ritual in our household. I wonder if Charlie has any thoughts about it. Looking at him sunning himself on our front porch makes me think about a deeper question: How much do animal minds resemble ours? Do other species have thoughts and feelings and memories the way we do?

As humans, we still think of ourselves as exceptional beings, fundamentally different from other animals. Over the past half century, though, scientists have amassed evidence of intelligence in many nonhuman species. New Caledonian crows snip twigs to fish insect larvae from tree trunks. Octopuses solve puzzles and shield their dens by placing rocks at the entrance. We no longer doubt that many animals possess impressive cognitive abilities. But are they more than just sophisticated automatons, occupied solely with survival and procreation?

LIKE FAMILYTo observe an octopus, marine biologist David Scheel brought Heidi to live with him and his daughter. As Scheel sipped his morning tea, Heidi stretched, yoga-like, in her aquarium. When the family watched TV, Heidi watched TV. When they returned home, she swished about. “She was happy to see us,” Scheel says. “Or seemed happy.”
PHOTOGRAPH BY QUINTON SMITH, PASSION PLANET

A growing number of behavioral studies, combined with anecdotal observations in the wild—such as an orca pushing her dead calf around for weeks—are revealing that many species have much more in common with humans than previously thought. Elephants grieve. Dolphins play for the fun of it. Cuttlefish have distinct personalities. Ravens seem to respond to the emotional states of other ravens. Many primates form strong friendships. In some species, such as elephants and orcas, the elders share knowledge gained from experience with the younger ones. Several others, including rats, are capable of acts of empathy and kindness. (Learn more about the hidden world of whale culture.)

This emerging picture of sentience, of rich inner lives, among surprisingly varied nonhuman species represents something of a Copernican revolution in how we view other beings on our planet. Until about three decades ago, the minds of animals were not considered a topic worthy of scientific inquiry. “And animal emotions—well, that was for romantics,” recalls Frans de Waal, an Emory University ethologist who has spent a lifetime studying primate behavior. De Waal was one of the earliest voices advocating for the recognition of animal consciousness. Starting a couple of decades ago, he says, scientists began to concede that certain species were sentient but argued that their experiences were not comparable to ours, and thus not significant.

A SENSE OF SELFA Japanese macaque stares at its reflection in a moped mirror. Some monkeys appear to recognize the image that they’re seeing as themselves, as do apes. Scientists use the so-called mirror test to determine if animals exhibit self-awareness. In humans this attribute develops around 18 months or later. 
PHOTOGRAPH BY JASPER DOEST

Now some behaviorists are becoming convinced that “the inner processes of many animals are as complex as those of humans,” de Waal says. “The difference is that we can express them in language; we can talk about our feelings.” This new understanding, if it becomes widely accepted, could spark a complete rethinking of how humans relate to and treat other species. “If you recognize emotions in animals, including the sentience of insects, then they become morally relevant,” de Waal says. “They are not the same as rocks. They are sentient beings.”

The scientific quest to understand the inner lives of animals, however, is still a relatively nascent enterprise. It’s also controversial. In the view of some scientists, knowing the mind of another species is next to impossible. “Attributing subjective feelings to an animal by looking at its behavior is not science—it’s just guessing,” says David J. Anderson, a neurobiologist at the California Institute of Technology who studies emotion-linked behaviors in mice, fruit flies, and jellyfish. Researchers investigating emotions such as grief and empathy in nonhumans must fend off the charge that they could be anthropomorphizing their subjects.

‘The inner processes of many animals are as complex as those of humans. The difference is that we can express them in language; we can talk about our feelings.’

FRANS DE WAAL, ETHOLOGIST

The way to get closer to the truth is to test inferences made from animal behavior, says David Scheel, a marine biologist at Alaska Pacific University who studies octopuses. “If you look anecdotally through the ages, the notion that dogs are tightly bonded to specific individuals is very clear. But they are domesticated. Can a fox do the same thing? Does a wolf have that emotional range? Does an orca feel that level of attachment to the members of its own pod? Can a dolphin become friends with a group of fish or a scuba diver? Our intuitions lead us astray here all the time. You will get people whose intuition is, That’s fake. Whatever it is, that’s not friendship, and other people who think, Well, that’s just silly. You are denying animals their inner lives.”

BODY LANGUAGESows, illuminated by light rings, are photographed by animal behavior scientists at Scotland’s Rural College. The images are analyzed using an algorithm by experts at the University of the West of England to detect subtle facial expressions. “We are at the stage of reading emotional states in pigs, which is a pretty remarkable achievement,” says Emma Baxter, a Rural College researcher.
PHOTOGRAPH BY EVGENIA ARBUGAEVA

If anthropomorphizing is an assault on scientific thinking, I stand guilty of indulging in it. I take delight in watching videos that show animals displaying behaviors suggesting a range of emotions we identify with. A water buffalo in a zoo enclosure working hard to flip over a turtle that’s flailing on its back, then acknowledging cheers from onlookers with what sure looks like a self-satisfied air. A panda sledding down a snow-covered hill, then trudging up to do it again. A monkey on the edge of a canal peeling a banana and gaping with dismay when it plops into the water. I show these videos to my wife all the time, a foolish grin plastered on my face. The idea that life all around us could be pulsating with emotion gives me a happy feeling.

These musings are not scientific, obviously, but what scientists do recognize is that emotions didn’t evolve in humans alone. Fundamentally, emotions are internal states that drive an animal to act a certain way. We may not think of hunger and thirst as emotions, but they are similar in that they are also internal states that compel action. Scheel describes them as primordial emotions. “When you gotta pee, you will get out of bed on a lazy Saturday morning and go to the bathroom, because you have little choice. It is getting imperative,” he explains.

READY RECALLA sheep ponders two numbers to pick the one it was taught to recognize. Sheep are good at this. They also remember faces, a high-level social skill. University of Cambridge researcher Jenny Morton says that although sheep are known to flock, they’re easy to work with when alone. “They trust their handler,” she says. “Trust requires emotional intelligence.”
PHOTOGRAPH BY EVGENIA ARBUGAEVA

Just like that invisible “imperative,” primordial emotions like fear prompt particular actions. Even though emotions like love and sorrow might seem more profound, they are not qualitatively different. “All of our scientific and philosophical work right now,” Scheel says, “is pointing to the idea that any emotion you care to name, however lofty and high and ethereal, is built up from these primordial emotions.”

If that’s the case, it’s not hard to appreciate that a wide variety of species—from fleas to chimpanzees—have emotions, primal in some and advanced in others.

The ravens regarded me warily, hopping away when I stepped too close to the wire mesh that separated us. Sunlight filtering into the cage shimmered off their silken, jet-black feathers, accentuating their sheen. I’d flown all the way from the United States to Austria to visit them because Thomas Bugnyar, a behavioral and cognitive biologist at the University of Vienna, had made a remarkable discovery about their behavior. After about 10 minutes, the birds seemed to relax. One cautiously shuffled over to get a better look at me, turning its head and sizing me up alternately with its left eye, then its right.

STILL LIFEKnopfi, an Australian shepherd being studied at the University of Vienna, learned how to lie motionless in a magnetic resonance imaging machine. Observing dog brains, scientists have found activity in areas similar to those in humans. Words of praise lit up a dog’s reward centers. Videos of caregivers activated regions tied to attachment.
PHOTOGRAPH BY JASPER DOEST

Corvids—the family that includes ravens—are known for their intelligence. Scientists have shown that they can use tools, solve problems, and plan for the future. During my visit, I watched one try to hide a treat. First, it placed a small rock over it and walked away. Minutes later, apparently not satisfied, it returned to pick up the treat in its beak, hopped over to a different location, and buried it in the gravel.

Ravens have impressive cognitive abilities, but they also display behaviors that suggest another facet to their intelligence: empathy. While studying raven behavior for his doctorate years ago, Bugnyar noticed that after two birds fought, a bystander that witnessed the squabble seemed to console the loser. He described a typical scene when I visited him in his office, under the gaze of a taxidermied raven—a wedding gift—perched on a branch.

“Two individuals engage in a fight. Now, the victim is chased around for a couple of minutes, eventually escapes into a corner, sits there shaking,” he told me. “And the other ravens are very aroused, they are flying around calling, and then one of them flies over to the victim, not directly towards the victim but nearby.” Making friendly calls, this raven inches closer until it’s within touching distance. If the victim moves away, the consoler persists. “After a couple of minutes, it ends up grooming the other one.”

THE NOSE KNOWSChanga, a chimpanzee at Germany’s Leipzig Zoo studied by Max Planck Institute researchers, inspects a thermal imaging camera. When humans are stressed, their noses get cooler. Scientists  also found colder noses in chimps that listened to recordings and watched videos of chimps fighting. Seeing a person they knew who appeared to be wounded had the same effect, suggesting the chimps felt empathy. 
PHOTOGRAPH BY SEBASTIAN SCHÜTTE AND JOHANNA ECKERT, MPI FOR EVOLUTIONARY ANTHROPOLOGY

Bugnyar documented 152 such encounters. He and a colleague, Orlaith Fraser, found that the ravens showing support usually knew the victims well. Researchers had seen consolation behavior in chimpanzees and bonobos; Bugnyar’s study was among the first to find it in birds.

Scientists have been able to investigate the phenomenon in greater detail by conducting experiments with rats. In one designed by Inbal Ben-Ami Bartal, a neuroscientist at Tel Aviv University, a rat is confined inside a transparent plastic tube with holes. The tube has a door that can be opened from the outside. The researchers place the tube inside a cage with another rat that is free to move around. The rat inside the tube squirms in a bid to escape. Its distress is visible to the other rat, which begins circling the tube, biting it, trying to dig underneath it. After a few sessions, the free rat figures out how to open the door. Once it has learned this trick, the free rat wastes no time in liberating the trapped rat.

This helpful behavior, though, is contingent on whether the free rat feels a sense of kinship toward the confined one. A free rat raised with others of the same genetic type will help a trapped rat of that type, even if it is a stranger. But if the trapped rat is of a different genetic type, the free rat remains unperturbed by its plight and doesn’t let it out. However, if a rat from one genetic type grows up with rats of another, it helps rats only of that other type, including strangers, while ignoring the distress of rats of its own type. “So, it’s not about biological similarity,” Ben-Ami Bartal tells me. “It’s about loving who you’re with. It’s about having your family and knowing that that’s your family.”

SHIMMERING MINDSRavens have remarkable cognitive abilities. Their sharp memories enable them to recall whether a particular person is kind or cruel. They display complex emotional abilities, such as consoling ravens vanquished in a fight, and are keenly attuned to their role in social networks. They also seem to be able to assess what other birds know, a highly advanced level of understanding.
PHOTOGRAPH BY TIM FLACH

A necessary feature of emotional intelligence—including the capacity to respond to a fellow creature’s distress—is the ability to read the emotional state of others. On a windy morning, I stood on the edge of a muddy field in the English countryside as psychologist Leanne Proops showed me how she’s testing whether horses have this ability.

It’s evident Proops, a researcher at the University of Portsmouth, loves her study subjects. Throughout my visit, every time I saw a horse and remarked how sweet the animal seemed, her smile would widen, and her eyes would soften. “Very sweet!” she would reply, invariably.

We leaned two boards against a fence, each printed with a life-size photograph of a horse’s head seen from the front. In one, the horse’s ears were perked up, the nose and mouth were relaxed, the eyes looked calm—a content horse. In the other, the horse had a threatening look, with ears pulled back, jaws clenched, and nostrils flared.

MIRROR IMAGEMagpies—like ravens, a member of the corvid family—are one of a few non-mammals to pass the mirror test. When they spot a mark on their body visible only in a reflection, they try to remove it. This indicates they realize they’re seeing themselves. Birds have small brains and no cerebral cortex, but they make up for it with a high density of neurons.
PHOTOGRAPH BY TIM FLACH

A graduate student led a reddish brown horse out of a barn: our first study subject. She walked it around for a couple of minutes before leading it to the two horse faces, then removed the lead rope. What we wanted to observe was how the horse would respond to the photographs. Would it show greater interest in the happy horse face or the other one?

Proops held her breath. The horse stared briefly at the two images and then sauntered to a corner of the field, swishing its tail and gazing at the grassy meadow beyond. Proops had warned me this might happen. Whimsical subjects can confound animal scientists.

The student brought out a splotchy gray-white horse with a soft, shiny mane. This one was more compliant. It stood for a few minutes, contemplating the photos, then went up to the happy face and nuzzled the photo.

Proops and her colleagues put 48 horses through a test like the one I watched. Some had a choice between images of a happy and an angry horse, some were presented with a happy face and a neutral face, and yet others with a neutral face and an angry face. When given a choice between the happy and the neutral ones, the horses had no preference. But they almost always avoided the angry face if it was shown to them, convincing the researchers that horses could recognize the expressions of a horse they had never met.

TO THE RESCUE“Rats,” says Inbal Ben-Ami Bartal, a neuroscientist at Tel Aviv University, “show the basic components of empathy.” In a study, she tested the rodents to see whether they would free another rat trapped in a tube. She discovered that they help only those belonging to their own social group. Adolescent rats, though, don’t discriminate.
PHOTOGRAPH BY PAOLO VERZONE

In another study Proops did, a horse was shown a photograph of a human face that was either smiling or angry. The photograph was shown in the morning. In the afternoon, the person in the photo—or an altogether different person—sat down in front of the horse, with a neutral expression. If the photo the horse had seen happened to have an angry expression, seeing that person in the afternoon caused the horse to display signs of stress. It looked at the person more with the left eye than the right—a behavior horses show when they see a potential threat—tensed up its nose and mouth, and drew its ears back. If the horse saw the photo of a happy face, or if the visitor was a different person, it tended to have a positive or neutral reaction. The findings from this study, also tested on 48 horses, suggest that horses might have a nuanced ability to read and respond to emotional states not only in horses but in humans too. The behavior demonstrates highly advanced skills of recognition and memory. “They’ve had to transfer from a photograph to a real person. They’ve had to remember a specific person and, obviously, remember the particular emotion,” she said.

“That’s amazing,” I remarked.

“Yeah, yeah,” she said, beaming. “It is.”

Horses might have a nuanced ability to read and respond to emotional states not only in horses but in humans too. 

Occasionally, Charlie moans and twitches in his sleep. I can imagine a nightmare that would frighten him—watching a truck bear down on him. He gets jumpy around large, noisy vehicles. But when I stroke his head to soothe him, I’m left wondering what he was dreaming. I’m not alone in wishing I could know what’s going on inside the mind of an animal.

When Christina Hunger, a speech-language pathologist who lives in Chicago, brought home a puppy four years ago, she had the same desire. In her work helping children with language delays, Hunger uses a communication device—a board with buttons that produce prerecorded words. She wondered if her blue heeler–Catahoula mix, Stella, could be trained to press buttons for words such as “water,” “play,” and “outside.” Stella was a quick learner and after about a month started using the buttons to verbalize those desires. One day, when Hunger was watering her houseplants, Stella ran to the other room, pressed the button for “water,” and came back to continue watching Hunger.

RING IT UPA beluga in an aquarium in Hamada, Japan, blows a bubble ring. Known to be playful, belugas have been observed making a variety of bubbles with their blowholes and mouths, in essence creating their own ephemeral toys. Often, when one starts to bubble, others join in. Play may have evolved to form social bonds and learn skills, but scientists think animals also like to have fun.
PHOTOGRAPH BY HIROYA MINAKUCHI, MINDEN PICTURES

“Her water dish was full. She didn’t take a drink of water. She was just using the word in a new way,” Hunger says. Stella appeared to be simply pointing out what she had seen.

Excited by the prospect of learning more about Stella’s inner life, Hunger introduced her to a few dozen more words, such as “help,” “bye,” “no,” and “love you.” One evening, Stella had something important to say. “She walked over to the ‘eat’ button and said, ‘Eat,’ and then walked across our apartment to her ‘no’ button and said, ‘No,’ ” Hunger recalls. “So she combined those two words to let us know she hadn’t eaten dinner.”

Hunger then put the buttons in one place—48 in all—to make it easier for Stella to use multiple words, which led to an explosion in communication. “She started combining words together—every day, multiple times a day—to create new messages that I had never taught her that were perfectly consistent with what was happening in the environment at the time,” Hunger says. She chronicled her experience in a best-selling book, How Stella Learned to Talk.

HAND UP OR HANDOUT?A rescued orangutan named Anih reaches toward Syahrul, an employee of the Borneo Orangutan Survival Foundation who has cared for Anih for years. Anih watched Syahrul struggle to walk in the mucky canal, the photographer says, and finally offered a hand. The photo went viral, but foundation officials caution against anthropomorphizing animal behavior. They think Anih probably was asking for food.
PHOTOGRAPH BY ANIL T. PRABHAKAR

One day this past spring, Hunger was on the phone when Stella tried to get her attention. She first pressed the buttons for “look,” “come,” and “play.” Hunger was busy, so Stella kept trying different versions of the same message, including “Want. Play. Outside.” Finally, frustrated, she pressed “love you,” followed by “no.” Hunger was flabbergasted. “I never thought that I would introduce a ‘love you’ button for her to tell me, ‘Love you. No,’ when she’s mad at me,” she says. “But it’s just amazing to see all the thoughts that are going on in her head.”

Stella isn’t the only dog to have opened a window to her inner life in this way. In recent years, other dog owners have used communication devices with their pets. The trend prompted Federico Rossano, a cognitive scientist at the University of California, San Diego’s Comparative Cognition Lab, to launch a study in which almost 3,000 dog and cat owners have sent reports of their pets using buttons to express words.

PAYING RESPECTResearchers have found ample evidence that elephants, like dolphins and whales, grieve. They’ve seen the animals linger where their relatives have died, rather than leave to forage for food. And they’ve watched elephants, like these in Botswana, gently touch the bones of their kin with their trunks. “It was curiously and heartbreakingly similar to that of a mourning ritual,” says Beverly Joubert, a photographer and National Geographic Explorer.
PHOTOGRAPH BY BEVERLY JOUBERT

Rossano says he’s seen numerous examples of dogs inquiring about a family member because the person has been absent. They express their desire to play with specific doggy friends by combining the word “park” with the name of the dog. “It’s fascinating how many instances we see where there’s two animals in the household and one asks the human for help for the other one,” he says. In one video he shared with me, a terrier named Bastian watches his housemate, an old cat named Hallie, sit down because she’s having trouble moving. He runs over to the buttons and presses “concerned” and “walk.”

I haven’t signed Charlie up for this study, but I can imagine he might be eager to tell me what he thinks of my making fun of his lack of sniffing talent all these years: “Funny. No.”

Diana Reiss, Whose eyes light up when the subject is marine mammals, was filming bottlenose dolphins in an aquarium in the 1980s when she made a startling discovery. She saw one swim to the bottom and exhale a ring of air from its blowhole. As this silvery ring was rising to the surface, the dolphin blew a second, smaller one that rose faster than the first, merging with it to make a bigger ring. The dolphin then swam through it. Reiss, now a cognitive psychologist at Hunter College, couldn’t believe what she was seeing. “This was the first time you saw an animal create its own object of play themselves,” she says.

GRIEF OBSERVEDA short-finned pilot whale tows a dead calf near the Canary Islands, a behavior also seen in orcas. Scientists increasingly think animals grieve. Asha de Vos, a Sri Lankan marine biologist and National Geographic Explorer, notes that pilot whales live in family pods. “Mourning is a reflection of the strong social bonds that are formed through their lifetimes,” she says.
PHOTOGRAPH BY JORDI CHIAS, NATURE PICTURE LIBRARY

It wasn’t a one-off. Reiss and others have since observed dolphins in aquariums make rings and toy with them in myriad ways. In the wild, dolphins play chase with one another. They’re just one of many species—in addition to dogs and cats, as everyone knows—that engage in play. Baboons have been seen teasing cows by pulling their tails. While studying elephants in Africa, Richard Byrne, who researches the evolution of cognition, often observed young elephants pursue animals that posed no threat, such as wildebeests and egrets. Scientists also have collected evidence of playful behaviors in fish and reptiles, according to Gordon M. Burghardt, an ethologist at the University of Tennessee, Knoxville. He’s observed Vietnamese mossy frog tadpoles repeatedly riding air bubbles released from the bottom of a tank all the way to the top.

Play expends energy and even risks injury, yet it does not always serve an immediate purpose. So why do animals engage in it? Researchers believe play evolved because it helps strengthen bonds between members of social groups. It also helps animals practice skills, such as running and leaping, that improve their chances of survival. That’s the explanation for why play evolved, but what’s the impulse that makes an animal engage in it? A plausible answer—according to Vincent Janik, a biologist at the University of St. Andrews in Scotland—is the pursuit of joy. “Why does an animal do something? Well, because it wants to,” he says. In the absence of any other benefit in the moment, it seems likely that play gives animals pleasure, enriching their inner life.

LOVE THY NEIGHBORViktor, a bonobo at the Fort Worth Zoo in Texas, is known for interacting with visitors. Frans de Waal, an expert on primate behavior, thinks bonobos may have a greater sense of empathy than humans. In bonobos, he says, areas of the brain responsive to the distress of others are larger and pathways to tamp aggression more developed.
PHOTOGRAPH BY VINCENT J. MUSI

How rich are the inner lives of animals that live in social groups, as we do? Anthropologist Sarah Brosnan of Georgia State University conducts experiments to try to peer into the minds of capuchin monkeys. She took me on a walk around the research facility, which houses six groups of capuchins. Each group has its own outdoor wire-mesh enclosure where the monkeys hang out for most of the day—eating or grooming or playing. It was the middle of the afternoon, and the staff had just finished scattering food.

Of all the food the capuchins get there, grapes are a favorite. Brosnan used that knowledge to devise an experiment to probe their emotional life. She put two capuchins in side-by-side compartments separated by a wire mesh and played a game with them. In the game, which the monkeys learned quickly, they had to hand a “token” to Brosnan—a small object, like a piece of wood—to receive a reward. Sometimes Brosnan gave both capuchins a piece of cucumber, which the animals liked about as much as kids like oatmeal. Other times, she offered one capuchin a cucumber slice and the other a grape. In a third arrangement, there was only one capuchin. Brosnan rewarded this lone monkey with cucumber, but every time she did, she also dropped a grape into the empty compartment.

When both monkeys got cucumber pieces, they ate them without complaint. But when one monkey kept getting a grape, the one stuck with cucumber became visibly upset. It dropped the cucumber or flung it toward Brosnan. The unfairness—or the inequity—was evidently too much for it to handle. In the test with just one monkey that saw grapes accumulating in the adjacent compartment, the animal initially tended to refuse the cucumber but over time went back to eating it. “So they don’t seem to mind the contrast as much as they mind the inequity,” Brosnan says. The study suggests that an expectation of fairness—and a sense of grievance when it’s not met—is probably not unique to humans.

In the absence of any other benefit in the moment, it seems likely that play gives animals pleasure, enriching their inner life.

Some primates appear sophisticated enough to have a sense of humor. There is consensus among researchers that chimps—and other great apes—laugh, usually when they’re playing. But they also have been seen laughing in other contexts. De Waal tells the story of a colleague who put on a panther mask and emerged out of the bushes across a moat from some chimpanzees. “And the chimps were very angry and threw all sorts of things at him,” de Waal says. Finally, the researcher, who was familiar to the chimps, took off the mask and revealed himself. “And some of the chimps—the older chimps—they laughed at this.”

I learned of another example from Marina Davila-Ross, a psychologist at the University of Portsmouth, who showed me a video of a young chimpanzee named Pia that she had filmed at an animal park in Germany. Davila-Ross caught the chimp pulling her father’s hair in what looked like an attempt to initiate play. When he didn’t respond, Pia lay down on the grass.

Shortly after, without any triggering event, Pia’s face opened into a wide smile. Then she broke into what can only be described as exuberant laughter, throwing her head back and folding her arms over her eyes, like a child watching a hilarious cartoon.

In Davila-Ross’s interpretation, which she includes in a recent research paper, Pia could have been laughing at her recollection of the playful moment with her dad. That surmise can’t be proved, of course, but her spontaneous mirth points to an interplay between memory and emotion that would suggest a more complex inner life than we might have imagined. Watching the video brought an immediate smile to my face. I made a mental note to show it to my wife.