Are animals humanly grieving? Scientists and animal lovers have long wondered on the question. We understand that all humans have a universal experience of grief when they lose loved ones, but little is known about the emotional worlds of animals. Elephants lingering at the carcasses, dogs seen to retire following the loss of a friend, we are increasingly seeing evidence that grief is not a human trait.
A revolutionary study published in 2025 by scientists at University College London, in Biology Letters, pursues this question further by looking at the reactions of rhesus macaque mothers (Macaca mulatta) to the deaths of their babies.
The findings shatter suppositions regarding animal sorrow, and open up fresh perspectives in the expanding discipline of comparative thanatology the examination of how various species react to death.
Why Study Grief in Animals?
Human grieving is marked by such changes in behavior as decreased appetite, apathy, anxiety, and social isolation. Although such symptoms might appear maladaptive, two reasons have been advanced by evolutionary biologists:
Byproduct hypothesis Grief is an emotional by-product of close social relationships. When a loved one dies, distress is caused by the brain that it is a permanent separation.
Adaptive hypothesis Grief could be selected as it is an indicator of loyalty and commitment, which is valued in social groups.
The examination of animal grief would be useful in understanding whether these mechanisms are human specific or that they have deep mammalian origins.
The Research: Observing Mothers After Loss.
The study was done over the free ranging group of rhesus macaques in Caribbean Primate Research Center in Cayo Santiago, Puerto Rico. The authors looked at 11 bereaved mothers whose infants died naturally compared to 11 matched controls (women of comparable age with no infants) over three months in 2022.
Those investigating behaviors paralleling human grief were interested in:
Hypersomnia and stupor (symptoms of a depression like withdrawal)
Vomiting profile (loss of appetite)
Displacement responses (self scratching, self grooming indicators of stress)
Grooming and interpersonal communication (social withdrawal)
The mothers were observed following 20-minute sessions each, and the time they spent at the activities was noted.
Key Findings
To their astonishment, the findings failed to conform to human patterns of grief:
Less Resting: During the initial 2 weeks following the infant loss, bereaved mothers had shorter resting periods than control females. This was contrary to what was expected, which was that they would turn lethargic.
No Significant Change: There were no distinct differences between bereaved and non bereaved females in feeding, grooming or stress related behaviour.
Short Term Response: The only apparent effect appeared to be a temporary depression of rest not of despair.
Results: Protest vs. Despair.
Researchers hypothesise that macaque mothers can also pass through a stage of protest mourning as primate babies do when they do not see their mothers. This stage is characterized by impatience, hyperactivity and increased motion. However, unlike humans, the mothers did not develop a period of desperation in the grieving process that is marked with lethargy and withdrawal.
The difference poses some interesting questions:
Do primates have bereavement recovery wiring?
Is grief in its human manifestation a specially protracted reaction conditioned by culture and thought?
Is the separation reaction in animals possibly a response of agitation, rather than of grief?
Alternative Explanations
The researchers point out three other possible explanations of their results:
No Grief at All? Macaque mothers maybe do not grieve in a similar manner to humans.
Limitations of the sample size: Only 11 bereaved mothers were used, and subtle changes of behavior could have been overlooked.
Personal variations: As human grieving differs across the board, so may that of the primate mothers, based on age, personality, or age of the infant at death.
Interestingly, mothers of very small babies (usually less than 2 weeks old) may not have experienced sufficient closeness to be able to grieve. This may be the reason why responses were subdued.
Why This Matters
This work is among the earliest systematic surveys of maternal grief in non human primates. Its results drive the field of comparative thanatology in a more subtle direction:
Grief is not necessarily one but a two stage process; protest (temporary agitation) and despair (permanent withdrawal).
Not every single species not even every single individual may evolve into despair.
Social complexity, caregiving and survival strategies could be associated with the evolution of grief.
Comprehending grief in animals not only broadens our research on evolution and cognition, but also reveals how we treat animals in zoos, sanctuaries and conservation.
Conclusion
Do macaque mothers grieve? It seems to be yes but not as humans. They respond with momentary restlessness, instead of a lasting sadness and withdrawal. This makes us question our anthropocentric understanding of mourning and realize that feelings in animals are multi layered, varied and have a long evolutionary history.
Further studies using more samples, physiological evidence (such as stress hormones), and comparisons of animals across different species will assist us in realizing the extent of grief, as we know it in the animal world. What becomes evident though is that grief human or animal is not pertainable to death, but rather the attachments that constitute life.
Reference
Johnson, E.A., Talyigás, F., & Carter, A. (2025). Macaque mothers’ responses to the deaths of their infants. Biology Letters, 21: 20240484.