Do Animals Know That They Will Die?

M oni the chimpanzee was still new to the Dutch zoo when she lost her baby. The keepers hadn’t even known that she was pregnant. Neither did Zoë Goldsborough, a graduate student who had spent months jotting down every social interaction that occurred among the chimps, from nine to five, four days a week, for a study on jealousy. One chilly midwinter morning, Goldsborough found Moni sitting by herself on a high tree stump in the center of her enclosure, cradling something in her arms. That she was by herself was not surprising: Moni had been struggling to get along with the zoo’s 14 other chimps. But when Goldsborough edged closer, she knew that something was wrong. Moni had a newborn, and it wasn’t moving.

Goldsborough raced downstairs to a room where the zookeepers were preparing food for the chimps, and told them what she’d seen. At first, they didn’t believe her. They said that Moni was probably just playing with some straw. After the keepers saw the baby with their own eyes, they entered the enclosure and tried to take it away from her. Moni wouldn’t part with it. They decided to wait and try again.

By this point, another female chimp named Tushi was lingering nearby. Tushi was one of Goldsborough’s favorites. A few years earlier, she’d achieved global fame for executing a planned attack on a drone that was recording the chimps for a documentary. Long before that, she’d had a miscarriage of her own. For Tushi, the sight of Moni and her baby may have brought back that memory, or even just its emotional contours. For the next two days, she stayed near Moni, who held the tiny carcass. Finally, in a tussle with the keepers, it fell from Moni’s grasp and Tushi snatched it up and refused to give it back. Moni grew extremely agitated. The keepers separated Tushi in a private room. Moni pounded at the door.

Goldsborough wasn’t sure how to interpret this behavior. Moni seemed to have been driven by fierce maternal attachment, an emotion that is familiar to humans. Tushi could have been responding to an echo of this feeling from deep in her past. But it’s not clear that either of the chimps really understood what had happened to the baby. They may have mistakenly believed that it would come back to life. It’s telling that we can’t say for certain, even though chimpanzees are among our nearest—and most closely watched—neighbors on the tree of life.

T his past June, more than 20 scientists met at Kyoto University for the largest-ever conference on comparative thanatology—the study of how animals experience death. The discipline is small, but its literature dates back to Aristotle. In 350 B.C.E., he wrote about a pair of dolphins that he’d seen gliding beneath the surface of the Aegean Sea, supporting a dead calf, “trying out of compassion to prevent its being devoured.” Most of the literature in comparative thanatology consists of anecdotes like these. Some are short, like Aristotle’s, but others, like the story of Moni and her baby, which was published in the journal Primates in 2019, and to which we shall return, contain extraordinary social details.

Scientists would like to go beyond these isolated scenes. They want to understand what feelings surge inside animals when they lose kin. They want to know whether animals are haunted by death, as we are. But they’re hampered by certain practicalities. They cannot interview animals (or at least not yet ). They can monitor their hormonal shifts—baboon cortisol levels spike when they lose someone close—but these can be triggered by other stressors. They don’t give us the texture and grain of their grief, if indeed it is grief that they feel.

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So far, the best comparative-thanatology data has come from observations of animals in the wild or captive populations in zoos. But here, too, there are problems. The species that react most interestingly to death—the usual suspects: nonhuman primates, whales, and elephants—have long lifespans. Their communities don’t lose individuals very often. Capturing systematic data about their reactions to death tends to require years’ or decades’ worth of work.

Alecia Carter, an evolutionary anthropologist at the University College of London, told me that she has identified a colony of more than 1,000 rhesus macaques on Cayo Santiago, an island off Puerto Rico, that would be perfect for such a study. The monkeys are highly social, and tend to live for 15 or 20 years—long enough to form deep relationships, but not so long that their deaths would be too few and far between. As a start, one of Carter’s grad students recently spent nearly a summer there collecting data. Only 11 monkeys died. “It was a great season for them, but terrible for us,” Carter said.

H umans have spent months in steamy jungles or zoo enclosures, dodging feces, to pursue this work. We are death-obsessed animals, after all, and have been since the dawn of recorded history, if not before. Our oldest work of epic literature tells the story of King Gilgamesh and his struggle with mortality. “Death is sitting in my bedroom, and wherever I turn, there too is death,” he says, before setting out in search of a plant that promises immortality. Human cultures have devised richly symbolic rituals to precede death and to follow it. For more than 10,000 years, we have laid our lost children in the ground, surrounded by flowers. We are a species of faithful mausoleum attendants, pyramid builders, inventors of the three-volley salute. We have imagined a great many afterlives for our dead, in heaven above or here on Earth aboard the great turning wheel of reincarnation. We have sicced our philosophers, armed with fine distinctions and caveats, on death; their definition of it now runs to more than 10,000 words. We have even projected our finitude onto the universe itself. Scientists tell us that it too will die after the last galaxies unwind and the black holes evaporate, particle by particle, trillions upon trillions of years from now.

These elaborate human conceptions of death are not passed down through our genes. They develop over decades in the minds of individuals, and in our cultures, they accrete over centuries. Human children tend to learn that death is not a temporary or reversible state somewhere between the ages of 4 and 7, or a bit earlier if they lose a beloved family member or animal. A 2004 paper in Cognition argued that, at this developmental stage, children understand death as a permanent loss of agency.

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In her new book Playing Possum: How Animals Understand Death , the Spanish philosopher Susan Monsó argues that many other animals likely share this simple concept of death. That may seem like common sense, but without access to their minds, it is difficult to know for sure. Mammals, fish, birds, reptiles, and insects are all cognizant of agency in the natural world. They monitor their environments for movement. They distinguish between inanimate objects and those that crawl or swim in pursuit of some goal. And some of them behave in ways that suggest an understanding that other animals can lose this agency forever. The hard part is knowing whether these behaviors flow from a conceptual recognition of death, or if they’re simply instincts.

Consider the termite. At the June meeting in Kyoto, an urban entomologist at LSU named Qian Sun presented a paper on the corpse-management practices of the eastern subterranean variety. More than 1 million of these insects may pack into labyrinthine underground colonies that sprawl for hundreds of feet. When worker termites come across a dead colleague in one of the colony’s tunnels, they react in different ways, depending on the state of the corpse. Fresh ones, they devour. Old and moldering ones, they bury. Other social insects that live in close quarters engage in similar practices. (Aristotle noted that bees carry their dead out of the hive.) But these behaviors don’t appear to be driven by a concept of death. Termite corpses produce oleic acid, which appears to trigger the burial behavior, as it does in several different social insects. When E. O. Wilson dabbed this chemical onto a live ant, its fellow colony members did not pause to consider whether the still-moving animal had suffered a permanent loss of agency. They simply carried it outside, even as it kicked its legs in protest.

C himps are not termites . Their large, complex brains are better-equipped to entertain a concept like death, and there is evidence to suggest that they feel something like grief. Several species of nonhuman primates have been known to gather around a community member that has recently died. In many cases, they will touch its body gently. These gatherings tend to dissipate slowly and in a patterned way: the individuals who were closest to the deceased animal stay longest. Jane Goodall observed an eight-year-old chimp lingering by his dead mother so long that he died, too.

Other mammals also tend to congregate around their dead. When giraffes do it, they swing their long necks at scavengers to keep them at bay. In India, the bodies of five young elephants have been found with branches and dirt scattered over them, leading some scientists to suggest that they’d been buried. André Gonçalves, an expert in comparative thanatology from Kyoto University, cautioned me about making too much of this anecdote. The elephants were found in trenches that they may have fallen into, he said. The dirt and branches could have piled up as family members tried desperately to dig them out.

In her book, Monsó argues that too much has been made of all these grief responses. She reminds her readers that animals live in a bloody world where predators pounce in the dark of night, or plunge down, talons-first, from unseen heights. The lurid violence of their environment provides a rich text for understanding death. Monsó imagines a young stag watching a dominance struggle between two older bucks. After their horns crack together a few times too many, the weaker combatant fails to get up. The young stag begins to understand the basics of mortality. If the lesson doesn’t take, he will likely have many occasions to relearn it.

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This education would presumably be accelerated in carnivores, who see death frequently and at close range. Gonçalves told me that he’s not so sure. Many animals eat other animals while they are still alive, he said. It’s not clear that they are trying to bring about death, or that they conceive of it as a separate state of being. They might simply be trying to get a moving food source into their mouths, like frogs that shoot their sticky tongues at everything moth-like, just as a matter of reflex. Gonçalves noted that even the precise one-bite kills deployed by big cats are instinctual, not learned behaviors.

Among chimpanzees, acts of wanton violence, up to and including murder, suggest a deeper understanding of death. Like wolves and lions—and people—chimps sometimes team up to kill members of rival groups. These attacks can have an air of premeditation. Two or three males will cross into terrain occupied by another group. They will move quickly and with stealth, and won’t stop to eat, even when passing by prime food sources. They target lone victims, and coordinate their attacks to avoid sustaining bruises or cuts of their own. In some cases, they will keep on striking long after a victim has signaled submission and let up only when the unlucky animal has ceased to breathe.

If indeed chimpanzees do have a concept of death, it is not as layered or intricate as ours; that much is certain. Humans know what death is, and we know that someday it will happen to us. James Anderson, an emeritus professor at Kyoto University, who is widely regarded as the godfather of comparative thanatology, has argued that chimps do not have a similar sense of their own mortality. He does not believe that anyone has ever really seen a chimp attempt suicide, in all the many thousands of hours that we have observed them. According to Anderson, only an animal that knows that it can die will try to bring about its own death. That there are no reliable reports of chimps, he says, or any other animals, engaging in this behavior suggests that the existential burden of mortality is uniquely ours to carry.

Anderson doesn’t know for sure, of course. Comparative thanatologists aren’t really in the business of giving answers, at least not yet. They can tell us that a chimp’s conception of death is grander than a termite’s, but much else is mysterious and maybe always will be. We can only hope that by continuing to watch chimps, we will notice new behaviors that betray a bit more of their interiority, or at least give us new grounds to speculate. The story of Moni and her baby may be one of them. Before coming across it, I’d read many papers about the way that chimps react to their deceased, but very few about how they treat the bereaved.

After the zookeepers got Tushi alone, they decided to let things cool off. They kept her away from the others until the next day. In the meantime, for Moni, everything had changed. She had previously struggled to connect with her fellow chimps in the enclosure. She had a way of pulling other females’ fur too hard during grooming, and she often sat too close to them, staring awkwardly. On the day that Tushi rejoined the group, Moni was surrounded by the other chimps. When she saw Tushi, she leapt up to perform an aggressive threat display. She even slapped her.

Tushi didn’t fight back, and in the 30 days that followed, she and the other chimps interacted with Moni more than they ever had before. No other chimp experienced an equivalent increase in attention. Almost all of the chimps contributed. They embraced Moni and gave her extra body kisses. But they did not contribute equally. Some cared for Moni more than others, and none more than Tushi. Something important seems to have passed between the two chimps. A few months later, things largely went back to normal in the enclosure. Moni stopped getting extra kisses. The males started bullying her again. But she and Tushi still often sat together. Even today, I am told, they remain close.

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