A groundbreaking study by researchers at University College London (UCL) delves deep into the enigmatic behavioral responses of macaque mothers following the death of their infants, challenging long-held assumptions about grief as a uniquely human experience. Published in the esteemed journal Biology Letters, this research provides an unprecedented and systematic examination of primate mourning behaviors, revealing that while macaque mothers undergo a brief period of physical agitation after the loss of their offspring, they do not exhibit the extended emotional suffering characteristic of human grief.
The study meticulously monitored 22 female macaques residing on Cayo Santiago, an island off Puerto Rico known for its free-ranging primate population. Half of these mothers had recently endured the tragic death of an infant, with losses averaging sixteen days prior to the onset of observation, while the other half remained infant-bereaved-free, serving as a critical control group. Over sixteen days, behavioral data were collected using CyberTracker software on smartphones, providing highly granular insights into a range of activities including resting, feeding, grooming, and displacement behaviors such as pacing and self-touching.
Contrary to prior expectations that bereaved macaque mothers would exhibit increased resting behavior—mirroring certain human reactions such as lethargy or withdrawal—the findings revealed a counterintuitive pattern. Bereaved mothers spent notably less time resting during the initial two weeks following infant death. This heightened physical restlessness, the researchers propose, may be analogous to a ‘protest’ phase observed in primate mother-infant separation studies, wherein mothers demonstrate agitation at the separation but do not progress to ‘despair’ or other prolonged grief-related behaviors.
The notion of an initial ‘protest’ phase is reminiscent of reaction patterns identified in attachment and separation literature, where primates display heightened locomotion and agitation immediately after losing contact with their infants. However, the absence of a subsequent decline into behavioral despair in macaques contrasts sharply with human grief, where withdrawal and diminished appetite often prevail for extended periods. This divergence signals potential evolutionary distinctions in how species process bereavement, emphasizing the complexity and specificity of grief as potentially a uniquely human phenomenon.
This research holds profound implications for the burgeoning field of evolutionary thanatology, which seeks to understand death, bereavement, and grief through a comparative lens across species. Despite anecdotal claims by pet owners and popular culture references suggesting animal grief, there remains a dearth of empirical evidence supporting the existence of equivalent emotional experiences outside humans. The UCL study’s rigorous observational approach contributes a critical empirical baseline, substantiating that while certain primate species exhibit initial behavioral disruptions following loss, these do not align with human definitions of grief marked by sustained behavioral or emotional withdrawal.
Intriguingly, the macaque mothers’ behavior displayed no significant variation in other key activities such as feeding, grooming, or displacement behaviors, which further reinforces the selective nature of their response to infant death. The targeted reduction in resting time suggests a distinct, short-lived disruption rather than a generalized malaise or depressive state. Such specificity invites a reevaluation of how scientists interpret observed ‘grief-like’ behaviors in animals, highlighting the necessity of distinguishing between genuine emotional states and mere behavioral consequences of social loss or environmental change.
The differentiation between bereavement—the objective condition of having lost a conspecific—and grief—the subjective, emotional experience accompanying such loss—emerges as a pivotal conceptual framework in this study. By separating these constructs, the researchers emphasize that observable behavioral changes do not necessarily equate to affective experiences akin to human grief. This nuanced perspective is vital for reframing future research endeavors in animal psychology and anthropology, advocating for more sophisticated methodologies to discern between outward expression and internal emotional states.
UCL anthropologist Dr. Alecia Carter, co-author of the study, expressed surprise at the findings, noting “Following the loss of an infant, we anticipated increased resting behaviors among macaque mothers, paralleling human patterns of bereavement.” Instead, she observed an unexpected reduction in resting, underscoring a short but intense period of agitation rather than prolonged withdrawal. This observation aligns with earlier studies on maternal disturbance in non-human primates, suggesting that the immediate post-loss period triggers a behavioral alarm that quickly subsides.
Lead author Emily Johnson, an MSc student at UCL Anthropology, reflected on the broader implications of the study, remarking, “Grief and our responses to death vary widely, even among humans. Our exploration into primate behaviors following infant death challenges assumptions that grief is a universal, cross-species experience.” Johnson advocates for expanded inquiry into the evolutionary roots of grieving behavior, positing that while animals may broadly respond to loss, grief as a sustained psychological state might be a more complex, uniquely human attribute.
Adding a technical dimension, the study’s observational methodology underscores the critical role of technology in ethology. The use of CyberTracker software on mobile devices facilitated precise, real-time behavioral logging amidst naturalistic conditions, minimizing observer bias and disturbances. This approach sets a methodological benchmark for future animal behavior research, combining technological innovation with rigorous scientific scrutiny.
The researchers call for future studies to harness cross-disciplinary tools from neuroscience, psychology, and anthropology to deepen the understanding of animal responses to death and bereavement. Integrating hormonal assessments, neural imaging, and longitudinal behavioral tracking could illuminate whether the absence of overt grief behaviors corresponds to the absence of underlying emotional processes, or if more subtle affective states remain undetected by current observational techniques.
Ultimately, this UCL study reframes grief within an evolutionary context, delineating the behavioral contours of mourning in macaque mothers and challenging narratives rooted in anthropomorphic interpretations of animal emotion. The findings contribute significantly to discourse on animal welfare, evolutionary biology, and the social complexities of primate species, marking a pivotal step towards comprehending the rich tapestry of life’s emotional experiences across the animal kingdom.
Subject of Research: Animals
Article Title: ‘Macaque mothers’ responses to the deaths of their infants’
News Publication Date: 16-Apr-2025
Web References:
DOI: 10.1098/rsbl.2024.0484
Keywords: Primates, Grief, Mothers, Animal research, Nonhuman primates, Animal locomotion, Animal psychology, Animals, Anthropology, Social sciences
