It has been observed in nature many times by researchers: Primate species ranging from baboons and apes carrying their babies around after they have died. It also happens in non-primate species. However, it is not known what the motivation or purpose behind this behavior.
A new study, which is the most comprehensive analysis of this behavior in primates, suggests that infant corpse carrying (ICC), could be part the grieving process. There are also links between the strength and duration of the mother-infant relationship.
This research examined 126 studies that covered 409 cases in which primate mothers responded to the death or near death of their infants. The analysis included 50 primate species. 80 percent showed some type of ICC behavior.
"Our study suggests that primates may be capable of learning about death in similar ways as humans. It might take experience to realize that death results in a prolonged 'cessation in function', which is one concept of death that humans have," Alecia Carter, an anthropologist at University College London (UCL), in the UK.
"What we don’t know and may never know is whether primates are able to understand that death is universal and that all animals, including humans, will die."
Although it is difficult to determine if primates understand that their infants are dead, research shows that infanticides or accidents were more common in younger mothers.
ICC was most common in Old World monkeys and great apes. These two species also had the longest lives after their deaths, which meant that ICC was more frequent. The infants who died younger were therefore more likely to be bonded with their mothers and carried them for longer periods of time.
Climate was not taken into account. The 409 cases of infants being carried around by their mothers were not all the same. Lemurs and other primates don't exhibit ICC behavior, but they do occasionally return to the body to keep mother-infant contact.
"Our study also showed that primate mothers might gain greater awareness of death through experience with external cues and death, and so 'decide not' to take their dead infant with them," said Elisa Fernndez Fueyo, a biological anthropologist at UCL.
Researchers point out that our shared evolutionary history suggests that primate social connections are similar to ours. However, more research will be needed to determine exactly what is happening here.
It is possible that infant death was treated in the same manner as how we see primates here. This could explain why the modern rituals surrounding death evolved from the ancient human practice of infanticide.
The team is now looking for more links between primates and humans in relation to their thanatological behavior. They have created ThanatoBase, a website that allows researchers to collect more information about primates' reactions to death and their feelings.
Carter says that Carter's study has implications for our understanding of grief processing among non-human primates. "It is known that human mothers who have experienced a stillbirth and can hold their baby are less likely than those who suffer from severe depression. This is because they are able express their love.
"Some primate mothers may need to take the same time as their children, which shows how important maternal bonds can be for primates and mammals in general."
Proceedings of the Royal Society B has published the research.
