Death among primates: a critical review of non-human primate interactions towards their dead and dying

Carrying the dead: behavior of a primiparous capuchin monkey mother and other individuals towards a dead infant

The evolutionary origins of caring for dead conspecifics are not completely understood. While nonhuman animals' understanding of changes in the state of a dead conspecific is debated, some exhibit behaviors consistent with experiencing emotional distress. Among nonhuman primates, the most common behavioral patterns related to the death of a group member include carrying and taking care of the deceased individual. The behavioral responses of the mother and other conspecifics towards a dead infant can be quantified to explore the underlying mechanisms and the evolutionary roots of these behaviors. Here, we report and quantify a probable case of infanticide in a wild group of capuchin monkeys, Sapajus xanthosternos, followed by the carrying and caring of the corpse by a primiparous mother. In our observation, the female maintained contact with the dead infant for 90% of the observed time, allowing other group members to approach and inspect the dead body, although only adult females and youngsters showed interest. The carrying of the corpse despite locomotion challenges, grooming and protecting it, and the apparent gradual adjustment to its unresponsive state (evidenced by unconventional carrying) suggest a potential coping strategy for dealing with the lack of feedback from the deceased. This study contributes to the field of comparative thanatology by documenting post-mortem behaviors in a primate species for which no prior record exists, broadening our understanding of such responses beyond humans.

Death, love, and evolution: Conceptions of death beyond terror

Recent years have seen an influx in interest on the role of death anxiety in human behavior. Terror Management Theory prevails as the leading theoretical and empirical paradigm utilized in the literature; however emerging research has revealed serious shortcomings with the paradigm. In this paper we examine the concept of death anxiety from a socio-evolutionary perspective. We outline how the attachment system evolved to prevent death during an extended period of juvenile vulnerability and is further co-opted into adulthood to maintain survival. Through a broader understanding of contemporary evolutionary thinking, including attachment theory, we propose that the hitherto inconsistent and amorphous definition of death anxiety be more usefully re-conceptualized as a fear of premature death. We explore how this re-conceptualization can be used to help explicate phenomena that existing paradigms have until now struggled to explain.

Recognising depression in non-human primates: a narrative review of reported signs of depression

Major depressive disorder (depression) is a highly heterogenous human mental disorder that may have equivalents in non-human animals. Research into non-human depression teaches us about human depression and can contribute to enhance welfare of non-human animals. Here, we narratively review how signs of depression in non-human primates (NHPs) can be observed based on symptoms of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Furthermore, we propose diagnostic criteria of NHP depression and we review reports on signs of depression in NHPs. We diagnose an NHP with depression when it shows a core sign (depressed mood or anhedonia) alongside at least three other DSM-5-derived signs of depression. Results show that four out of six observable signs of depression are present in NHPs, occasionally lasting for months. However, only a group of six NHPs in one study met our proposed criteria for a diagnosis of depression. We call for more research into the co-occurrence of depressive symptoms in individual NHPs to establish the prevalence of depression in NHPs.

Necrophilic behaviour in wild stump-tailed macaques (Macaca arctoides)

Necrophilic behavior (attempted copulation with corpses) has been scarcely reported in non-human primates, especially in the wild. Here is the first case of necrophilic behavior observed in wild stump-tailed macaques in Thailand. Six groups of total N > 460 individuals have been identified and habituated. The corpse of an adult female was found and directly observed for 2 days and by camera trap for 3 days. The cause of death could not be identified, but no prominent physical injury was detected. Within 3 days of the observation, three different males attempted copulation with the corpse. Noteworthy for this observation was that not only males in the group of the dead female but also males from different groups interacted with the corpse. Taken together, these observations suggest that some cues emanating from the corpse coupled with a nonresistant/passive orientation may have triggered these responses in the males. Given that necrophiliac responses have been scarcely reported in non-human primates, our findings provide new insight into these behaviors and to comparative thanatology in general.

Reactions to a dead adult female in Japanese macaques at Arashiyama: Why did a non-affiliated female groom the corpse?

Reporting reactions to death in nonhuman primates can provide valuable information for understanding the evolutionary origin of human ways of dealing with death. Although many studies have reported nonhuman primates' reactions to infant corpses, less is known about their reactions toward dead adults or adolescents. The deaths of adult primates, who usually form complex social relationships, may have social impacts. Here, we described in detail the reactions of Japanese macaques (Macaca fuscata) to the corpse of an adult female in a free-ranging multi-male multi-female group. We analyzed quantitative data on the whole group to determine how death-related behaviors were related to social relationships. Most group members in this case, including social partners of the deceased, exhibited no notable interest in the corpse. Only one adult female, who was not a grooming partner of the female before she died, touched and groomed the corpse. We examined four possible reasons why this female groomed the corpse: unawareness of death, learning about death, desire to consume insects, and reputation-building with other group members. This study highlights the potential value of closer examination of associations between reactions to dead adults or adolescents and social relationships before and after death in primate groups.

Dead-infant carrying by chimpanzee mothers in the Budongo Forest

It has been suggested that non-human primates can respond to deceased conspecifics in ways that suggest they experience psychological states not unlike humans, some of which could indicate they exhibit a notion of death. Here, we report long-term demographic data from two East African chimpanzee groups. During a combined 40-year observation period, we recorded 191 births of which 68 died in infancy, mostly within the first year. We documented the post-mortem behaviour of the mothers and describe nine occasions where Budongo chimpanzee mothers carried infants for 1-3 days after their death, usually until the body started to decompose. We also observed three additional cases of extended carrying lasting for more than 2 weeks, one of which was followed by the unusual extended carrying of an object and another which lasted 3 months. In each case, the corpses mummified. In addition, we report four instances of recurring dead-infant carrying by mothers, three of whom carried the corpse for longer during the second instance. We discuss these observations in view of functional hypotheses of dead-infant carrying in primates and the potential proximate mechanisms involved in this behaviour.

Thanatology in the northern muriqui (Brachyteles hypoxanthus)

Primate thanatology, or the study of primate responses to dying and death, has become increasingly relevant in recent years. However, the number of reports remains small and the quality of published records is highly variable. Here, we extend the literature on comparative thanatology with observations on a population of the northern muriqui (Brachyteles hypoxanthus). We compiled all seven cases of muriqui responses to dead, dying, or abandoned infants observed by trained researchers of the Muriqui Project of Caratinga between 1998 and 2020. Four different adult females were observed carrying their dead offspring (n = 4) and one of these females was also observed carrying her dead grand-offspring (n = 1). Five of the seven cases involved dead newborns, one involved a newborn abandoned by its mother on the forest floor, and one involved a 1.6-year-old infant that was visibly ill and died after its mother left it on the ground. Dead newborns were carried for 1-3 days, and all cases occurred during the dry season months. No other age-sex classes were observed to interact with the dead or dying immatures. Our observations are consistent with hypotheses concerning the predominance of dead-infant carrying in other primates, and with the effects of climate on rates of corpse disintegration. They also show the value of long-term studies for obtaining and understanding anecdotal records of rare behavior.

Staring death in the face: chimpanzees' attention towards conspecific skulls and the implications of a face module guiding their behaviour

Chimpanzees exhibit a variety of behaviours surrounding their dead, although much less is known about how they respond towards conspecific skeletons. We tested chimpanzees' visual attention to images of conspecific and non-conspecific stimuli (cat/chimp/dog/rat), shown simultaneously in four corners of a screen in distinct orientations (frontal/diagonal/lateral) of either one of three types (faces/skulls/skull-shaped stones). Additionally, we compared their visual attention towards chimpanzee-only stimuli (faces/skulls/skull-shaped stones). Lastly, we tested their attention towards specific regions of chimpanzee skulls. We theorized that chimpanzee skulls retaining face-like features would be perceived similarly to chimpanzee faces and thus be subjected to similar biases. Overall, supporting our hypotheses, the chimpanzees preferred conspecific-related stimuli. The results showed that chimpanzees attended: (i) significantly longer towards conspecific skulls than other species skulls (particularly in forward-facing and to a lesser extent diagonal orientations); (ii) significantly longer towards conspecific faces than other species faces at forward-facing and diagonal orientations; (iii) longer towards chimpanzee faces compared with chimpanzee skulls and skull-shaped stones, and (iv) attended significantly longer to the teeth, similar to findings for elephants. We suggest that chimpanzee skulls retain relevant, face-like features that arguably activate a domain-specific face module in chimpanzees' brains, guiding their attention.

Cloning and Embryo Splitting in Mammalians: Brief History, Methods, and Achievements

Embryo splitting is one of the newest developed methods in reproductive biotechnology. In this method, after splitting embryos in 2-, 4-, and even 8-cell stages, every single blastomere can be developed separately, but the embryos are genetically identical. Embryo splitting, as an approach in reproductive cloning, is extensively employed in reproductive medicine studies, such as investigating human diseases, treating sterility, embryo donation, and gene therapy. In the present study, cloning in mammalians and cloning approaches are briefly reviewed. In addition, embryo splitting and the methods commonly used in embryo splitting and recent achievements in this field, as well as the applications of embryo splitting into livestock species, primate animals, and humans, are outlined. Finally, a perspective of embryo splitting is provided as the conclusion.

Why do some primate mothers carry their infant's corpse? A cross-species comparative study

Non-human primates respond to the death of a conspecific in diverse ways, some of which may present phylogenetic continuity with human thanatological responses. Of these responses, infant corpse carrying by mothers (ICC) is the most frequently reported. Despite its prevalence, quantitative analyses of this behaviour are scarce and inconclusive. We compiled a database of 409 published cases across 50 different primate species of mothers' responses to their infants' deaths and used Bayesian phylogenetic regressions with an information-theoretic approach to test hypotheses proposed to explain between- and within-species variation in ICC. We found that ICC was more likely when the infant's death was non-traumatic (e.g. illness) versus traumatic (e.g. infanticide), and when the mother was younger. These results support the death detection hypothesis, which proposes that ICC occurs when there are fewer contextual or sensory cues indicating death. Such an interpretation suggests that primates are able to attain an awareness of death. In addition, when carried, infant age affected ICC duration, with longer ICC observed for younger infants. This result suggests that ICC is a by-product of strong selection on maternal behaviour. The findings are discussed in the context of the evolution of emotion, and implications for evolutionary thanatology are proposed.

First observation of a chimpanzee with albinism in the wild: Social interactions and subsequent infanticide

Albinism—the congenital absence of pigmentation—is a very rare phenomenon in animals due to the significant costs to fitness of this condition. Both humans and non‐human individuals with albinism face a number of challenges, such as reduced vision, increased exposure to ultraviolet radiation, or compromised crypticity resulting in an elevated vulnerability to predation. However, while observations of social interactions involving individuals with albinism have been observed in wild non‐primate animals, such interactions have not been described in detail in non‐human primates (hereafter, primates). Here, we report, to our knowledge, the first sighting of an infant with albinism in wild chimpanzees (Pan troglodytes schweinfurthii), including social interactions between the infant, its mother, and group members. We also describe the subsequent killing of the infant by conspecifics as well as their behavior towards the corpse following the infanticide. Finally, we discuss our observations in relation to our understanding of chimpanzee behavior or attitudes towards individuals with very conspicuous appearances.

Observations of wild non‐human primates with albinism are extremely rare

We report the first observation of a chimpanzee with albinism in the wild

We describe interactions between the infant with albinism and other group members

We describe the subsequent infanticide of the individual with albinism

We discuss these observations in light of our understanding of chimpanzee behavior

Are They Really Trying to Save Their Buddy? The Anthropomorphism of Animal Epimeletic Behaviours

Simple Summary

Anthropomorphism, defined as attributing human traits to animals and other entities, seems to have appeared during evolution to improve an individual’s understanding of other species (or indeed the world in general). Yet anthropomorphism can have beneficial or harmful consequences especially for animals, and there seems to be little interest in monitoring the potential danger of this approach. Few studies have focused on the factors affecting how we attribute intentions or beliefs to animals, and more quantitative studies are needed to identify how and why humans attribute mental states and cognitive abilities to other animals. In this study, participants answer questions about three videos in which an individual (a sparrow, an elephant and a macaque, respectively) displayed behaviours towards an inanimate conspecific that suddenly regained consciousness at the end of the footage. A fourth video showed a robot dog being kicked by an engineer to demonstrate its stability. These questions were designed to measure how far participants attribute humanlike intentions, beliefs or mental states to non-human animals and robots. Men and older participants are less likely to attribute humanlike mental states to animals. Similarly, people who work with animals or have at least one pet at home demonstrated less naïve anthropomorphism. Conversely, we found that members of animal protection associations showed more biophilia (affinity for other living organisms), attributed more intentions and mental states to animals and were further from biological reality (current scientific knowledge of each species) than non-members. Understanding the potential usefulness of these factors can lead to better relationships with animals and encourage human-robot interactions.

Abstract

Anthropomorphism is a natural tendency in humans, but it is also influenced by many characteristics of the observer (the human) and the observed entity (here, the animal species). This study asked participants to complete an online questionnaire about three videos showing epimeletic behaviours in three animal species. In the videos, an individual (a sparrow, an elephant and a macaque, respectively) displayed behaviours towards an inanimate conspecific that suddenly regained consciousness at the end of the footage. A fourth video showed a robot dog being kicked by an engineer to demonstrate its stability. Each video was followed by a series of questions designed to evaluate the degree of anthropomorphism of participants, from mentaphobia (no attribution of intentions and beliefs, whatever the animal species) to full anthropomorphism (full attribution of intentions and beliefs by animals, to the same extent as in humans) and to measure how far the participants had correctly assessed each situation in terms of biological reality (current scientific knowledge of each species). There is a negative correlation (about 61%) between the mental states attributed to animals by humans and the real capability of animals. The heterogeneity of responses proved that humans display different forms of anthropomorphism, from rejecting all emotional or intentional states in animals to considering animals to show the same intentions as humans. However, the scores participants attributed to animals differed according to the species shown in the video and to human socio-demographic characteristics. Understanding the potential usefulness of these factors can lead to better relationships with animals and encourage a positive view of human-robot interactions. Indeed, reflective or critical anthropomorphism can increase our humanity.

Spontaneous (minimal) ritual in non-human great apes?

The potential for rituals in non-human great apes (apes) is an understudied topic. We derive a minimal definition of ritual and then examine the currently available evidence for it in untrained and non-enculturated apes. First, we examine whether such apes show evidence for the two main components of our minimal definition of ritual: symbolism and copying. Second, we examine if there are actual cases already identifiable today that may fit all aspects of our minimal definition of ritual-or whether there are at least cases that fit some aspects (proto-ritual). We find that apes are not likely to spontaneously practise minimal ritual, but we claim that the highest expected likelihood of occurrence is in the results-copying domain. Yet, we did not find actual cases of minimal ritual in apes-including those involving environmental results. We did, however, find some cases that may match at least part of our minimal ritual definition-which we termed proto-ritual. At least two out of three potential cases of such proto-rituals that we identified (rain dance, object-in-ear and surplus nest-making procedures) do revolve around results. Overall, apes do not show much, or very clear, evidence for even minimal ritual, but may sometimes show proto-ritual. However, dedicated ape ritual studies are currently lacking, and future work may identify ape ritual (or clearer cases of proto-ritual). We discuss the implications of our preliminary finding for inferences of ritual in the last common ancestor of humans and apes. This article is part of the theme issue 'Ritual renaissance: new insights into the most human of behaviours'.

Homo neanderthalensis and the evolutionary origins of ritual in Homo sapiens

There is a large, if disparate, body of archaeological literature discussing specific instantiations of symbolic material culture and the possibility of ritual practices in Neanderthal populations. Despite this attention, however, no single synthesis exists that draws upon cognitive, psychological and cultural evolutionary theories of ritual. Here, we review the evidence for ritual-practice among now-extinct Homo neanderthalensis, as well as the necessary cognitive pre-conditions for such behaviour, in order to explore the evolution of ritual in Homo sapiens. We suggest that the currently available archaeological evidence indicates that Neanderthals may have used 'ritualization' to increase the successful transmission of technical knowledge across generations-providing an explanation for the technological stability of the Middle Palaeolithic and attesting to a survival strategy differing from near-contemporary H. sapiens. This article is part of the theme issue 'Ritual renaissance: new insights into the most human of behaviours'.

Issues of theory and method in the analysis of Paleolithic mortuary behavior: A view from Shanidar Cave

Mortuary behavior (activities concerning dead conspecifics) is one of many traits that were previously widely considered to have been uniquely human, but on which perspectives have changed markedly in recent years. Theoretical approaches to hominin mortuary activity and its evolution have undergone major revision, and advances in diverse archeological and paleoanthropological methods have brought new ways of identifying behaviors such as intentional burial. Despite these advances, debates concerning the nature of hominin mortuary activity, particularly among the Neanderthals, rely heavily on the rereading of old excavations as new finds are relatively rare, limiting the extent to which such debates can benefit from advances in the field. The recent discovery of in situ articulated Neanderthal remains at Shanidar Cave offers a rare opportunity to take full advantage of these methodological and theoretical developments to understand Neanderthal mortuary activity, making a review of these advances relevant and timely.

Why chimpanzees carry dead infants: an empirical assessment of existing hypotheses

The study of non-human primate thanatology has expanded dramatically in recent years as scientists seek to understand the evolutionary roots of human death concepts and practices. However, observations of how conspecifics respond to dead individuals are rare and highly variable. Mothers of several species of primate have been reported to carry and continue to interact with dead infants. Such interactions have been proposed to be related to maternal condition, attachment, environmental conditions or reflect a lack of awareness that the infant has died. Here, we tested these hypotheses using a dataset of cases of infant corpse carrying by chimpanzees in Gombe National Park, Tanzania (n = 33), the largest dataset of such cases in chimpanzees. We found that mothers carried infant corpses at high rates, despite behavioural evidence that they recognize that death has occurred. Median duration of carriage was 1.83 days (interquartile range = 1.03-3.59). Using an information theoretic approach, we found no support for any of the leading hypotheses for duration of continued carriage. We interpret these data in the context of recent discussions regarding what non-human primates understand about death.

Responses to death and dying: primates and other mammals

Although some definitions of thanatology-broadly definable as the study of death and dying-exclude nonhumans as subjects, recognition of the scientific value of studying how other species respond to sick, injured, dying and dead conspecifics appears to be growing. And whereas earlier literature was largely characterized by anecdotal descriptions and sometimes fanciful interpretations, we now see more rigorous and often quantitative analysis of various behaviors displayed towards conspecifics (and sometimes heterospecifics) at various stages of incapacitation, including death. Studies of social insects in particular have revealed chemical cues that trigger corpse management behaviors, as well as the adaptive value of these behaviors. More recent research on other taxonomic groups (including aquatic and avian species, and mammals) has sought to better document these animals' responses to the dying and dead, to identify influencing factors and underlying mechanisms, and to better understand the physiological, emotional, social and psychological significance of the phenomena observed. This special issue presents original short reports, reviews, and full research articles relating to these topics in New World monkeys, Old World monkeys and apes, as well as equids and proboscids. The range of events, data, hypotheses and proposals presented will hopefully enrich the field and stimulate further developments in comparative evolutionary thanatology.

Callitrichid responses to dead and dying infants: the effects of paternal bonding and cause of death

Many primates show responses to dead infants, yet testing explanations for these behaviors has been difficult. Callitrichids present a unique opportunity to delineate between hypotheses, since unlike most species, male caretakers form closer social bonds with infants than mothers. Callitrichids are also known to commit infanticide, leaving obvious wounds that may enable them to more readily recognize death. We present: (1) a case study of a wild common marmoset (Callithrix jacchus) group responding to an infant's natural death, and (2) a review of published infant deaths across callitrichids (N = 16), testing for trends in the sex of reacting individuals and cause of death. In our case study, several group members frequently interacted with the dead infant, attempting to carry it. However, the strongest response was from a male that remained with the corpse for ~ 3 h, despite his group leaving the area. Across callitrichid species, corpse interactions were significantly sex-biased: 100% (N = 6) of accidental deaths involved corpse interaction by males (p = 0.007), compared to 60% (N = 3 of 5) by females (p = 0.095). Cause of death also played a significant role, with individuals attempting to carry dead infants in 100% (N = 6) of accidental deaths, but only 11.1% (N = 1 of 9) of infanticides (p = 0.001). Although the available literature is small and potentially subject to publication biases, these data support the idea that visually obvious wounds may influence callitrichids' perception of dead conspecifics. Additionally, male-biased patterns of corpse interaction in callitrichids indicate that social bonds likely shape reactions to the dead, in addition to kinship. While published data on primate thanatology are limited, this study demonstrates quantitative approaches that can provide empirical insights into primates' responses to dead conspecifics.

Reaction to the death of the oldest female in a group of chimpanzees at the Municipal Zoological Garden, Warsaw

In March 2017, the oldest female of a group of chimpanzees living in the Municipal Zoological Garden in Warsaw, died in her sleep at the age of 53, due to natural causes. The article reports reactions of the eight other individuals in the group, four males and four females, including the daughter and the granddaughter of the old female, the following day. The corpse generally elicited more interest in the females than in the adult males. The females touched the body gently and groomed it more often than the males, who tended simply to look at and sniff it. However, the most diverse reactions, ranging from gentle touching to jumping on and hitting the corpse, were seen in the youngest male. By contrast, the oldest male never approached the corpse. In general, the chimpanzees at the zoo reacted in a manner much milder than is often reported from the wild.

Primate thanatology and hominoid mortuary archeology

In recent years, a thanatology of primates has become a respectable research topic, and although still sparse, observations among several taxa have shown how complex responses to the dead can be. In human evolutionary archeology, re-analysis of old ‘burial’ sites is slowly revising our view on the development of specifically human responses to the dead. We propose here the means of integrating information from the two disciplines of primatology and archeology, in support of the field of primate thanatology. We propose a terminology and a shared set of research questions, from which we generate a number of observations that can be utilized in the field, in order to establish a working dialogue and foster greater collaboration across the two disciplines.

Prolonged care and cannibalism of infant corpse by relatives in semi-free-ranging capuchin monkeys

Cannibalism is a quite common behaviour in animals that can have survival value when food is scarce or in the case of overpopulation. Conversely, cannibalism can also increase pathogen transmission and reduce fitness. In primates, some cases of cannibalism are associated with infanticide or are performed by mothers after their newborn has died (filial cannibalism). We report here the first observation of cannibalism, specifically infant cannibalism, in a semi-free-ranging group of brown capuchin monkeys (Sapajus apella). The baby was likely stillborn, as parts of the cranial bones were missing and no fresh injuries were visible. After half a day of taking care of the dead infant, the mother ate part of the corpse's skin and the highly nutritional viscera, possibly thereby compensating for the physiological costs of pregnancy. After attentively watching his mother's behaviour, the older brother of the dead newborn similarly ate parts of the corpse. Although we cannot rule out idiosyncrasy and vertical social transmission, it is possible that cannibalism is a normal-albeit rare-part of the behavioural repertoire of capuchin monkeys.

Reaction to allospecific death and to an unanimated gorilla infant in wild western gorillas: insights into death recognition and prolonged maternal carrying

It is still unclear to what extent animals possess knowledge of death. Primates display a large variety and often contradictory behaviors toward conspecific corpses, particularly those of infants (e.g., prolonged carrying and care). This study reports on reactions in a wild, habituated western gorilla group (Gorilla gorilla, 11-13 individuals) in the Central African Republic to an unanimated conspecific infant, and to an allospecific corpse. Individuals' reactions were compared to their usual behavior using both continuous focal animal sampling and 10-min instantaneous scan sampling. In the first observation, an infant gorilla fell out of a tree and looked dead. The mother retrieved it and remained unusually close to another adult female, until the infant started to move again, almost 1 h later. Cases of infants regaining consciousness after almost-fatal accidents may act as positive reinforcement for continued carrying by mothers, which might be socially learned. In the second case, three immature gorillas reacted to a dead red river hog. For 20 min they stared at the corpse from tree branches above, while chest beating, defecating, and urinating several times. They showed fear and did not approach the corpse. These observations show that non-predatory species, such as gorillas, may be able to acquire and develop some knowledge about death even though they do not kill other vertebrates.

Responses to a dead companion in a captive group of tufted capuchins (Sapajus apella)

The observation of specific reactions by animals to dead conspecifics raises questions about their capacity to understand death. We describe the behavior of a captive group of tufted capuchins in the hours following the death of an adult female. The behavior of 12 subjects was recorded over a 5-h period. Most group members displayed exploratory behaviors toward the corpse, peering at it, smelling, touching, lifting or pulling it at least once. Interactions with the corpse were particularly frequent in the first hour, then decreased in the following hours. The relatives of the deceased female were the most involved individuals, and her daughter spent more time near her body than the other members of the group. Rates of interaction with the body were especially high in subadult individuals. Most of the behaviors directed to the body of the deceased individual appeared to be investigative.

Responses to dead and dying conspecifics and heterospecifics by wild mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes schweinfurthii)

Comparative ["evolutionary")] thanatology is devoted to investigating how animals respond to signs of death and dying, in conspecifics and other species. Responses to corpses often involve fear and confusion, and "deceased infant carrying" by females is widespread in nonhuman primates. Such behavior could result from "animacy detection malfunctions" (Gonçalves and Biro in Philos Trans R Soc (B) 373:20170263, 2018): corpses have attributes of animate agents, but-like objects-they do not act, but instead are acted upon by outside forces. Many or most nonhuman primates have core cognitive mechanisms for detecting animacy, but these might not resolve this paradox. Skeletons of conspecifics, seriously injured or ill individuals behaving oddly and not responding as expected to social acts and signals, and corpses, skeletons, and sick or injured individuals belonging to other species could trigger milder animacy detection malfunctions. A central question is whether any nonhuman primates learn from experience that death involves permanent loss of biological functionality and is universal. The relevant literature is mostly anecdotal or devoted to case studies, and this question is open. In response to calls for more information, I describe 25 cases of responses to corpses, skeletons, and mortally injured or ill individuals, both conspecifics and heterospecifics, seen during fieldwork on mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes schweinfurthii). Observations were generally consistent with the animacy detection malfunction hypothesis, although cases of prolonged deceased infant carrying are problematic. Also, one case in gorillas apparently involved sympathetic concern for a dying individual, and sympathetic concern might have occurred in a chimpanzee case.

Corpse-directed play parenting by a sterile adult female chimpanzee

The study of representational play in nonhuman primates, including chimpanzees (Pan troglodytes), provides interspecific perspectives on human cognitive development and evolution. A notable form of representational play in chimpanzees is play parenting, wherein parental behavior is directed at inanimate objects. Though observed in captivity, unambiguous examples of play parenting by wild chimpanzees are rare. Here, we report two cases from Ngogo in Kibale National Park, Uganda, in which a wild adult female chimpanzee (P. t. schweinfurthii) directed parental behaviors at corpses. Both cases involved the same adult female chimpanzee, aged 20-21 years. The first case was observed on 5 March 2016, and the play object was the corpse of a bushbaby (Galago thomasi); in the second case, observed on 6 May 2017, the play object was a recently deceased chimpanzee infant postmortally stolen from the mother. The chimpanzee possessed the first and second play objects for approximately 5.5 h and 1.8 h, respectively. In both cases, she performed a variety of maternal behaviors, including co-nesting, grooming, and dorsally carrying the play objects. In contrast to previous observations of play parenting in captivity, the play parent was a presumably sterile adult female, well beyond the average age of first birth. These observations contribute to the expanding literature on chimpanzee interactions with the corpses of both conspecifics and heterospecifics.