Dead Reckoning

Comparative thanatology confronts the Grim Reaper

“Man is the only animal that has to be encouraged to live” – Friedrich Nietzsche

When did humans begin to understand that life was finite, that death was an essential fact of life? And what does death mean for creatures other than humans? I think there are two aspects: the awareness that death is real and comes to us all, and the processing of it. For you and I this process amounts to acceptance, and grieving. The understanding, the taking it in and the dealing with it. The mourning.

I was once struck deeply by an image that was published in the November 2009 issue of National Geographic [see footnote 1]. The image depicted workers at Cameroon’s Sanaga-Yong Chimpanzee Rescue Center removing the body of a 40-year old female chimpanzee named Dorothy from the compound. She was lying in a wheelbarrow wrapped in a blanket with just her head showing; a worker cradles Dorothy’s head in her hands. In the background, on the opposite side of a wire fence, are 16 (at least) of Dorothy’s fellow rescued chimpanzees, male and female, old and young, present as if mourning. It is hard to deny that this was the case, but how were they processing this loss? How does a chimpanzee mourn? Chimpanzees are our nearest evolutionary relative, which may make it easier to accept that they possess this capacity, but how far does it extend into other animal domains? This question is the province of comparative thanatology, and it is fascinating!

James R. Anderson, emeritus professor of psychology at Kyoto University, has written several articles on chimpanzee responses to death among conspecifics, and on evolutionary approaches to comparative thanatology [see footnote 2]. He notes that among adult humans, the conception of death embraces four elements: inevitability (all organisms will die), irreversibility (there is no coming back from death), non-functionality (the dead do not perceive, think, feel or act) and causality (one or more vital functions has lost viability, through age, disease, injury etc.) [see footnote 3]. Though humans might broadly empathize when people unknown to us personally die, as a matter of shared humanity, it is the proximity of our relationship with a deceased person that is determinative of our personal grieving process. Does the same hold for other creatures? Writing in The Descent of Man in 1871 (p. 73, italics mine), Charles Darwin posed the question: “It is often difficult to judge whether animals have any feelings towards others’ sufferings. Who can say what cows feel, when they surround and stare intently on a dying or dead companion?”  

However, before we can approach animal grief, we must first ask another – do non-human creatures recognize that a conspecific has died, and if so, then how so? Put another way, how does a dead individual communicate the fact of their death to the living? What senses are at play; what thought processes?

Living creatures do one very significant thing that the non-living do not: self-propelled movement (aka animacy, of either body parts such as limbs, heads, eyes, or of whole bodies). At the same time, non-living organisms do one thing that the living do not do: decay, a process accompanied by characteristic ‘death scents’. Such scents are termed necronomes (cadaverine/putrescine, the strong odors associated with the break-down of amino acids or fatty acids). Perhaps those aspects – motion and decay – are good places to begin seeking clues for death detection!

In a 2018 publication, Gonҫalves and Biro noted that responses to a dead conspecific might include avoidance, consumption, or moving the remains, all of which tend to be elicited by unambiguous scents (chemical signals). It is likely that these responses are ancient, what evolutionary biologists refer to as ‘highly conserved’, suggesting a significant adaptive value. Responses such as avoidance (among vertebrates) or movement (among many eusocial insects such as ants or bees) would be highly adaptive in terms of predator avoidance or potential for disease transmission. Among humans, decades of research ponders the origin of funerary behavior, first definitively recognized for Neandertals, particularly burial of the dead and associated ritual activities. Burial might be considered the penultimate form of corpse movement (with the ultimate being corpse destruction, the modern form of which would include cremation). Currently, one can only wonder at the role of necromones as ‘potential threat signals’ as a motivating factor in the evolution of this behavior. We can wonder, however, which in and of itself is a beautiful thing!

The second indicator for death detection noted earlier is movement – or should I say, lack thereof in the ‘no-longer-living’. As the process of decay, and olfactory signs of such, occur some time after death, the absence of movement would be the first indication that a conspecific has passed on. Again, Gonҫalves and Biro discuss a number of aspects of non-scent elicited responses to death among a number of animal taxa, including corvids (crows, jays), proboscids (elephants), cetaceans (whales) and non-human primates. Mobbing behavior, body inspection and loud congregations are noted for many corvids species. Elephants have been observed to inspect a corpse with feet or trunks, vocalize, defend the body from predation and in some instances, females have carried the body of a dead infant for several weeks (a time frame in which putrescine odors would indeed also be present). Of course, there are the apocryphal stories of elephant graveyards, where elderly elephants would leave the herd to die among the remains of generations of conspecifics before them. While there is no evidence for such locations or behaviors, living elephants have been observed to interact intimately with the skeletal remains of dead elephants they come across, most especially skulls and tusks – interestingly, the latter an extant elephant might recognize also as a visible symbol of life.

We’ll consider non-human primates in more detail later, especially chimpanzee responses, but Gonҫalves and Biro discuss complex ‘thanatological behaviours’ among primate species when confronted with the inert body of a conspecific. These include mobbing, vocalizing, infant carrying, grooming, dragging, attempted sexual mounting, and beating among others. Transport of dead infants by the mother has been noted in both New and Old World primate species, and while the motivation for this particular response is not known, it has been hypothesized that physiological mechanisms (hormones) that act to form and strengthen the mother-infant bond may be at play.

When considering (any) behavior in the context of highly intelligent, social creatures such as primates it is fair to ask to what degree learning might play in the performance of such acts? If one female chimpanzee, for example, were to observe another female carrying her dead infant, might that translate at some point into the observer carrying her own dead infant in the future? A valid question for which we currently have no answer.

Let us return to grief and grieving, as inward and outward projecting manifestations of suffering. Among non-human animals, some of the more well-known instances of apparent grieving have been recorded among cetaceans. In 2018 an orca whale belonging to the Southern Resident pod inhabiting the Salish Sea off the southern coast of British Columbia, Canada, was recorded carrying the body of her dead calf for 17 days. This mother, J-35, was seen to this behavior in January of 2025. And, as I write this in September of the same year, another female member of the same pod, J-36, has been observed exhibiting the same behavior. Scientists monitoring these mammals refer to this response to the death of a calf as ‘a tour of grief’. Such incidents are in fact not isolated. In 2108, Melissa A.L.V. Reggente and several of her colleagues reported on 106 cases of what they referred to as epimeletic death responses (81 whales and 25 non-whales (e.g., sea otters)) across 28 different species of aquatic mammals. (Epimeletic behaviors involve healthy individuals providing care to injured, dying or dead conspecifics.) Differences in such behaviors between whales and non-whales were hypothesized to reflect maternal investment – whale calves are dependent upon their mothers for 5 – 10 years; non-whale calves for 1 year or less. But are ‘tours of grief’ by cetaceans bone vide indicators of grieving?

As an evolutionary question we might turn to our closest primate relatives for insight into grieving in non-human animals. As noted earlier, various primate species have responded to the dead body of a conspecific in numerous complex ways. Although groups members unrelated to the dead individual have been known to interact with a corpse directly (e.g., touching) or indirectly (e.g., visitation, guarding), the more intriguing relationships exist between a mother and her offspring, usually an infant. Here we need to consider – as noted earlier – the nature of the bond between mother and infant, which has been deemed the ‘most essential social bond among mammals’ [see footnote 4]. Most reports of these situations note that maternal carrying of a dead infant is typical, but highly variable in duration, from several days to weeks and even months. Interpretation of this behavior suggests a transition from an intense attachment to the body immediately after death toward a gradual lessening of this connection with the passage of time. This transition is associated with increasing permissiveness on the part of the mother to other group members interacting with the dead infant. How might this reflect the initial strength of the mother-infant bond and how it changes over time with increasing death awareness? And to what degree is the mother mourning the loss of the infant as opposed to the loss of the bond, i.e., the social connection of care-giving and response? It should also be noted that mothers carrying a dead infant, while the most common thanatological behavior observed among primates, is likely maladaptive, as it would be problematic for normal locomotion and thus interfere with foraging behavior and, in theory, predator avoidance.

In a 2019 review paper on primate thanatology, Gonҫalves and Carvalho tabulated 8 different hypotheses that have been proposed for why a primate mother might carry a dead infant. Given that many are not mutually exclusive, it is likely that carrying an infant’s corpse is not attributable to a single cause. Yet, among these various hypotheses, only one invoked the notion of bereavement, with Gonҫalves and Carvalho noting: “Carrying a dead infant may be a form of active grief-coping behaviour. The continued physical contact with the dead infant acts as an ‘emotional buffer’, relieving maternal distress and helping the mother adjust to the loss”.

Two final considerations to wonder about.

First, though a focus in this discussion has been on a mother’s response to the loss of an infant, death is not a one-way street. Infant and adolescent primates have shown complex behaviors attached to the death of a mother, perhaps most famously documented in the 1991 National Geographic film by Hugo van Lawick, ‘People of the Forest: The Chimps of Gombe’ in which the infant chimpanzee Flint is filmed over several days despairing the death of his mother, the matriarch Flo. Leaving artistic license and anthropomorphism aside, Flint is shown in a  depressive state and refusing to leave his mother’s corpse for several weeks, even to eat, and eventually dies [see footnote 5].

And second, as Gonҫalves and Carvalho suggest, does grief presuppose an awareness of death? Among humans, one of the defining features of death awareness is consolation, and while primates do show a range of complex thanatological behaviors, consolation does not appear to be among them. Consider that many social animals, living in groups marked by individuals coming and going (such as chimpanzees in fission-fusion societies), display greeting behaviors (vocalization, physical signals and contact) but only humans exhibit leaving behaviors – notably, chimpanzees do not. This leaves us to wonder then, is there a distinction to be had between a group member leaving with an expectation of return, and knowing that a group member is gone for good?

A final note: In considering how unique – or not – humans might be in awareness of mortality, their own or that of conspecifics, one relationship with death is undoubtably uniquely human. This is the capacity to look at life and ask: ‘Is it all worthwhile?’, and in consideration of the answer choose to take their own life. Nicholas Humphrey, psychologist, philosopher and emeritus professor in the London School of Economics, considered this exact question in his 2018 paper ‘The lure of death: suicide and human evolution.’ An interesting read.

Footnote 1: The photograph was taken by Monica Szczupider, a volunteer at the rescue center at the time. Dorothy died in September 2008 of congestive heart failure. She arrived at the center in 2000 following 25 years of abuse at a Cameroonian “amusement park” following capture after her mother was killed by a hunter. The image can be found here: https://www.nationalgeographic.com/travel/article/behind_our_photo_of_the_grievi 

Footnote 2: In 2018, Anderson and his colleagues, zoologist Dora Biro and archaeologist Paul Pettitt, coined the phrase evolutionary thanatology as a name for a new field of study that would examine diverse aspects of death-related processes and activities from multiple perspectives: biological, psychological, sociological, historical, physiological / archaeological and so forth. Such a field would also embrace responses to death and dying across species, from eusocial insects, to birds, aquatic forms, and of course non-human primates. 

Footnote 3: We are not concerned here with philosophical or cultural arguments around reincarnation. Anderson notes that, in children, an adult-level comprehension of death as something inevitable and irreversible appears around age 10.

Footnote 4: This assertation comes from a 2011 paper published by Katherine Cronin and her colleagues, reporting on interactions of a chimpanzee mother to the death of her 16-month-old infant.

Footnote 5: Van Lawick had been married to Jane Goodall (from 1964 to 1974) having met will he was filming the lives of chimpanzees at Gombe Stream National Park in Tanzania. The events of Flint and Flo are documented as well in Goodall’s 1986 book Chimpanzees of Gombe: Patterns of Behaviour.

Note: All of the 2018 articles mentioned in this piece come from a special issue of the Philosophical Transactions of the Royal Society B 373:20170263 issue titled: ‘Evolutionary thanatology: impacts of the dead on the living in humans and other animals’.