Do primate mothers grieve the loss of their infants in the same way that humans do? A new study from University College London, published in Biology Letters, sheds light on this question, revealing surprising differences in bereavement responses between macaque mothers and humans.
While human mothers often experience grief characterized by lethargy, appetite loss, and despair after the death of an infant, macaque mothers exhibit a different pattern. The study found that macaque mothers displayed a short period of physical restlessness in the first two weeks following their infant's death, spending less time resting than non-bereaved females. This restlessness, researchers suggest, could represent an initial "protest" phase, similar to what's observed in primate mother-infant separation studies. However, this phase wasn't followed by the extended period of "despair" or other behavioral markers of grief commonly seen in humans.
The researchers observed 22 macaque mothers at the Caribbean Primate Research Center on Cayo Santiago, Puerto Rico. Half of these mothers had recently lost an infant, while the other half served as a control group. The study systematically recorded behaviors like resting, feeding, grooming, and displacement behaviors (locomotion, pacing, self-grooming, self-touching) over a 16-day period using smartphones and CyberTracker software.
"Following the loss of an infant, we had expected the macaque mothers to spend more time resting, as is common among bereaved humans," said co-author Dr. Alecia Carter (UCL Anthropology). "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 behaviors."
This research contributes to the emerging field of evolutionary thanatology – the study of death, bereavement, and grief across different species. By understanding how different species respond to death, we can gain insights into the evolutionary origins of grief and its unique manifestations in humans.
Lead author MSc student Emily Johnson (UCL Anthropology) emphasized the importance of distinguishing between bereavement and grief in these studies. While bereavement simply describes the state of losing someone to death, grief encompasses the negative emotional and behavioral responses to that loss.
"Anthropologists have long questioned whether animals are capable of experiencing grief," Johnson said, "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."
The study highlights the complexity of grief and the need for further research to understand the diverse ways in which different species cope with loss. While primate mothers may not exhibit grief in the same way as humans, their responses to infant death provide valuable insights into the evolution and expression of emotions across the animal kingdom. Future studies could investigate other primate species and explore the underlying neurological and hormonal mechanisms involved in bereavement responses.
