Japanese macaques, close relatives of the toque and rhesus macaques. These monkeys live on the slopes of southern Japan’s Mount Takasakiyama. Infant mortality is high, as we would expect in a wild population; based on an intensive nine-year period of data collection, the death rate within a year of rhesus birth was 21.6 percent. Maternal carrying of the dead was observed over a twenty-four-year span, during which 157 cases were recorded out of 6,781 rhesus births. The researchers compiled statistics on factors like infant’s age at death and duration of corpse-carrying by the mother. Within a week of death, 91 percent of rhesus the infants had been abandoned by their mothers. The longest maternal carry lasted seventeen days, by which time the small carried body was decomposing, fly-ridden, and reeking with a bad odor. Most of the other monkeys avoided that mother, and when juveniles showed an interest in the decaying body, they were rebuffed by her.
In presenting these data, Sugiyama and his coauthors pose a key question: Does the carrying of dead infants signal maternal emotion or does it instead point to the mothers’ lack of awareness that their infants have died? The null hypothesis for this case must take into account the need for wild animals to budget their energy. The carrying behavior does, after all, represent a substantial energy expenditure by the mother. At Takasakiyama, the monkeys must traverse a steep hill every day, and with a dead infant in tow, mothers lose the free use of one hand. Their movement and their foraging are most certainly compromised. So why do they do it? What does it mean that mothers carried infants significantly more often if the death occurred within thirty days of birth? It was especially common if the infant lived more than one day but died within several days; as Sugiyama’s group notes, this pattern matches up with the time when the infant, not yet able to move around well on her own, begins to cling and breast-feed regularly. Not all dead infants were carried, however. It’s not as if some trigger associated with infant size, weight, or age pushes the mother into an innate response of carrying.
What’s most curious to me is that infants who lived longer, and who presumably enjoyed a longer period of emotional connection with their mothers, were not carried longer than infants who were barely known by their mothers. Taking all of the data together, I can’t see that the behaviors described for these monkeys fit comfortably with a claim of monkey grief.
Maternal corpse-carrying behavior has also been described by Peter Fashing and his colleagues, who study the gelada monkeys of Guassa, Ethiopia. Large-bodied and long-haired, the Guassa geladas dwell in the grasslands of the Ethiopian highlands. Over a three-and-a-half-year period, fourteen females at Guassa carried dead infants, some for only an hour, others for much longer. Most carrying episodes lasted between one and four days, with three females carrying their infants for significantly longer periods: thirteen, sixteen, and forty-eight days. In these extended cases, the infants’ bodies gradually became mummified, and as with the Japanese macaques at Takasakiyama, they emitted an unpleasant smell.
Forty-eight days is a long time to carry a dead body, and suggests to me a decisively willed action on the part of that mother. She resumed reproductive cycling while carrying her dead infant, and was even seen copulating while clutching the infant’s body with one hand. The timing of carrying and then abandoning the body cannot, in this case at least, be explained by hormonal changes that occur when an infant suddenly stops nursing. This mother carried her dead infant right through that period and beyond.
Beyond the length of the carrying episodes, what’s striking at Guassa is the interest shown in the corpse by females other than the mother. In two cases, juvenile females were allowed to carry and groom the bodies of
In presenting these data, Sugiyama and his coauthors pose a key question: Does the carrying of dead infants signal maternal emotion or does it instead point to the mothers’ lack of awareness that their infants have died? The null hypothesis for this case must take into account the need for wild animals to budget their energy. The carrying behavior does, after all, represent a substantial energy expenditure by the mother. At Takasakiyama, the monkeys must traverse a steep hill every day, and with a dead infant in tow, mothers lose the free use of one hand. Their movement and their foraging are most certainly compromised. So why do they do it? What does it mean that mothers carried infants significantly more often if the death occurred within thirty days of birth? It was especially common if the infant lived more than one day but died within several days; as Sugiyama’s group notes, this pattern matches up with the time when the infant, not yet able to move around well on her own, begins to cling and breast-feed regularly. Not all dead infants were carried, however. It’s not as if some trigger associated with infant size, weight, or age pushes the mother into an innate response of carrying.
What’s most curious to me is that infants who lived longer, and who presumably enjoyed a longer period of emotional connection with their mothers, were not carried longer than infants who were barely known by their mothers. Taking all of the data together, I can’t see that the behaviors described for these monkeys fit comfortably with a claim of monkey grief.
Maternal corpse-carrying behavior has also been described by Peter Fashing and his colleagues, who study the gelada monkeys of Guassa, Ethiopia. Large-bodied and long-haired, the Guassa geladas dwell in the grasslands of the Ethiopian highlands. Over a three-and-a-half-year period, fourteen females at Guassa carried dead infants, some for only an hour, others for much longer. Most carrying episodes lasted between one and four days, with three females carrying their infants for significantly longer periods: thirteen, sixteen, and forty-eight days. In these extended cases, the infants’ bodies gradually became mummified, and as with the Japanese macaques at Takasakiyama, they emitted an unpleasant smell.
Forty-eight days is a long time to carry a dead body, and suggests to me a decisively willed action on the part of that mother. She resumed reproductive cycling while carrying her dead infant, and was even seen copulating while clutching the infant’s body with one hand. The timing of carrying and then abandoning the body cannot, in this case at least, be explained by hormonal changes that occur when an infant suddenly stops nursing. This mother carried her dead infant right through that period and beyond.
Beyond the length of the carrying episodes, what’s striking at Guassa is the interest shown in the corpse by females other than the mother. In two cases, juvenile females were allowed to carry and groom the bodies of
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