LONDON — Primate mothers carry their dead infant’s body for up to several months as a way of grieving, according to new research. The largest-ever study of the behavior, known as “infant corpse carrying,” suggests that the mothers may possess an awareness of death, or be able to learn about it over time.
Researchers say that their findings have implications for our understanding of how non-human animals experience emotion. The University College London-led team compiled data from anecdotes reported in 126 publications on primate behavior, looking at 409 cases of infant corpse carrying across 50 species.
“Our study indicates that primates may be able to learn about death in similar ways to humans: It might take experience to understand that death results in a long-lasting ‘cessation of function’, which is one of the concepts of death that humans have. What we don’t know, and maybe will never know, is whether primates can understand that death is universal, that all animals — including themselves — will die,” says study co-author Dr. Alecia Carter, in a statement.
“Our study also has implications for what we know about how grief is processed among non-human primates. It’s known that human mothers who experience a stillbirth and are able to hold their baby are less likely to experience severe depression, as they have an opportunity to express their bond. Some primate mothers may also need the same time to deal with their loss, showing how strong and important maternal bonds are for primates, and mammals more generally,” she adds.
Four out of five species in the study (80%) were found to perform corpse-carrying behavior. Although widely distributed across the primate order, the behavior was found to most frequently occur in great apes and Old World monkeys, who also carried their infants after death for the longest durations.
The team found that the primate species was a strong determinant of whether the bodies of infants were carried. Primates that diverged long ago, such as lemurs, did not carry infant bodies after death. They were still found, however, to express grief through other behaviors, such as returning to the corpse or giving “mother-infant contact calls”.
Both the age of the mother at the time of the infant’s death and the way in which the infant died were found to influence the likelihood of infant corpse-carrying. The research team found that younger mothers were more likely to carry their infants after death. Traumatic deaths, such as infanticides or accidents, were less likely to result in corpse-carrying, compared to deaths caused by non-traumatic events, such as illness.
The study also reveals that among those species that carry their dead infants, the length of time spent carrying the corpse varies depending on the strength of the mother-infant bond, indicated by the age of the infant at the time of their death. Infants were carried for longer when they died at younger ages, with a sharp decline once they reached around half the weaning age.
“We show that mothers that were more strongly bonded to their infant at death carry the corpse for longer, with emotions possibly playing an important role. However, our study also shows that, through experience with death and external cues, primate mothers may gain better awareness of death and therefore ‘decide’ not to carry their dead infant with them, even if they may still experience loss-related emotions,” says study co-author Elisa Fernández Fueyo, also of UCL.
“We found that bonds, particularly the mother-infant bond, possibly drive primates’ responses to death. Because of our shared evolutionary history, human social bonds are similar in many ways to those of non-human primates. Therefore, it is likely that human mortuary practices and grief have their origins in social bonds. The thanatological behaviors that we see in non-human primates today may have been present in early human species as well — and they may have transformed into the different rituals and practices during human evolution. However, we need more data to enable us to further develop our understanding of this, and of the extent to which primate behaviors relating to death may not only be explained by bonds but also by the associated emotions and, thus, resemble human grief,” Fueyo adds.
The findings are published in the journal Proceedings of the Royal Society B.
South West News Service writer Stephen Beech contributed to this report.