Published in Biology Letters, the research reveals that bereaved macaque mothers rest significantly less in the first two weeks following their infant's death compared to non-bereaved mothers. This initial increase in activity may reflect a "protest" response, similar to those observed in previous studies on mother-infant separations in other primates.
However, the researchers found no subsequent phase of behavioral despair, which is commonly documented in humans coping with loss. The absence of such extended behavioral shifts suggests fundamental differences in how primates and humans experience grief.
This investigation marks the first systematic effort to compare death-related behavioral changes in primate mothers with those seen in human grieving processes. It adds new insight to the emerging field of evolutionary thanatology, which explores death and bereavement across species.
The study observed 22 female rhesus macaques at the Caribbean Primate Research Center on Cayo Santiago, Puerto Rico. Eleven mothers had recently lost infants, with an average time since death of 16 days, while the other eleven formed a control group. Researchers tracked behaviors such as resting, feeding, grooming, and displacement activities using the CyberTracker mobile application over a 16-day span.
Dr Alecia Carter of UCL Anthropology explained: "Following the loss of an infant, we had expected the macaque mothers to spend more time resting, as is common among bereaved humans. What we actually observed was the opposite. The bereaved macaque mothers spent less time resting in the first two weeks after an infant's death and there was no difference of their time spent foraging, grooming, or doing displacement behaviours."
She noted the brevity of this restlessness phase: "The mothers' period of restlessness was surprisingly short, but this short-term response can also be seen in primate mother-infant separation studies, which show a relatively short period of 'maternal disturbance' after separation from their infant."
Lead author and UCL MSc student Emily Johnson said: "Death is an inevitable part of life and how we respond to death can vary greatly, even among humans. We wanted to explore how the behavioural response to death, the experience of grief, differs between primates and humans. Is grief a uniquely human experience?"
The researchers drew a distinction between bereavement and grief, defining bereavement as the condition of having experienced a loss, while grief involves the emotional and behavioral manifestations of that loss.
Emily added: "Anthropologists have long questioned whether animals are capable of experiencing grief, and many pet owners will report their beloved cat or dog grieves after the death of a fellow pet. But these are reports from owners who are often themselves grieving. Grief-like behaviour, such as reduced activity, could simply be because they have lost a playmate.
"Our findings show no behavioural markers of grief in the way humans understand it among the macaque mothers, so we recommend further study in this area and greater data collection on primates' responses to bereavement."
Research Report:Paper Pending
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