Grieving baboon mothers in the wild carry their dead infants for up to 10 days in what researchers believe is a coping mechanism for dealing with their loss, according to a 13-year study on Namibian chacma baboons.

Chacma baboons live in large groups of up to 100 males and females and exhibit strong familial lines and hierarchies. Across a dozen observations of maternal responses to the deaths of their infants, including a miscarriage and two stillbirths, researchers found that the mother would carry her infant corpse for a varying amount of time, from one hour to 10 days. During this time, she grooms her infant frequently and treats the corpse much differently than she would a live infant, even one who is sick or lethargic.

"There are numerous hypotheses to explain primate responses to dead infants. Perhaps the strongest hypothesis is that carrying after death is an extension of nurturing behavior,” explained lead author Dr Alecia Carter, UCL Anthropology and Université de Montpellier, in a statement.

"We are not suggesting that the mothers are unaware that their infants are dead, but there is such strong selection on mother-infant bond formation that, once formed, the bond is difficult to break. It's less clear why only some mothers carry or protect their dead infant, but I suspect that a range of factors influences this behavior."

The unawareness hypothesis follows that the mother lacks the cognitive ability to understand the difference between an unresponsive and dead infant, further arguing that continued care is simply an adaptation in case the infant eventually recovers. Carter says this likely does not apply in chacma baboons as dead infants were seen carried by a limb or dragged along the ground – a behavior that is not observed with live infants. Instead, the researchers argue in Royal Society Open Science that mother chacma baboons are likely practicing what is known as “grief-management hypothesis”, whereby they carry their infant as a way of dealing emotionally with their loss. It is possible there is also an element of the “social-bonds hypothesis”, which argues that mothers carry their infants because of the intense social bond shared between the two during their lifetime.

Though the exact amount of time varies, it is likely impacted by the mother’s age, the cause of death, and perhaps the climate conditions.

"Other primates have been observed carrying their dead infants for much longer periods of time. Chimps and Japanese macaques, for example, have been observed carrying infants for over a month,” said Carter. “However, chacma baboons travel much longer distances on an average day and the desert environment is harsh, making it costly for a mother to carry her infant for long periods.”  

Males, usually the father, were also seen tending to and protecting the dead infant during this period. In one instance, a male was observed grooming the infant when the mother temporarily left.

"This is quite surprising behavior because it has rarely been reported by previous studies. Male baboons are not usually very paternal, but they regularly protect their infant from threats, especially from infanticidal attacks. That is where a male baboon kills another male's offspring in order to mate with the mother,” said study co-author Dr Elise Huchard, from Université de Montpellier.

The findings add to the scientific understanding of what is known as “thanatology”, or the study of reactions to death and dying and how that impacts surviving individuals. Understanding how animal responses differ from humans provides insight into the evolution of species’ minds and the origins of humanity’s awareness of death and dying.