These monkey mothers actually carry around the corpses of their young

Imagine a new mother walking down a sunny sidewalk in a big city. She has a coffee in one hand, a bag over her shoulder, and swaddled at her chest is an infant. She is happy. She is going about her daily routine. The only thing strange about the scene: the infant is dead.

For a human being, this may seem outrageous, but for Japanese macaques—with whom human beings share about 93 percent of our genome—the scene is not strange at all. In fact, it is common. According to a 2009 research paper published in the journal Anthropological Science, some 15 percent of infants that die within about the first year of life are carried around by their mothers for a period of time. “Japanese macaque mothers sometimes persist in carrying infant corpses until they are covered with flies and completely decayed,” the study reported. “Occasionally a corpse may be carried until it is mummified.”

On average, the mother macaques carried their infants for about three days. The longest recorded observation was a mother that carried her dead infant for 17 days.

The monkey’s that were observed in this study live on Mount Takasaki, located in southern Japan, a warm and humid region that does not receive snowfall. Temperatures here are much warmer than in Nagano Prefecture, on Japan’s main island of Honshu, where the snow monkeys that Digital Dying reported on earlier this week live. After running our article I received an email from Dr. Takafumi Ishida of the University of Tokyo, who passed along the Anthropological Science paper. The study was done over a 24-year period that began in 1971 and ran through much of the 2000s. The authors are a Kyoto University researcher, a municipal official from the nearby city of Oita, and a researcher from the Takasakiyama Natural Zoo.

This paper is unique because it attempts to stake out exactly why the mother monkeys carry around their dead infants. “In the absence of precise data, this behavior had previously been interpreted anthropomorphically as a reflection of maternal affinity for the infant,” the paper reported. “It is equally possible, however, that mothers lack a concept of death.” In other words, the macaques are carrying around their dead infants because they have failed to realize they are actually dead.

But to me this seems like a pretty dubious claim. How could any mammalian mother not know whether their offspring was alive or dead? For example, on numerous occasions cats have been observed trying to revive or resuscitate dead kittens. This seems to imply that the mama cat knows its offspring has crossed a threshold, from this place we call alive to this place called dead, and the mama cat is trying to bring the kitten back across that threshold. Our own anthropomorphic ranking of species places the cat below the monkey on a scale of intelligence. So if a cat knows its kittens are dead, how could a monkey not know its young ones are dead?

Either way, the practice, known as “infant-corpse-carrying behavior,” is exceptional in its sheer energy. The monkeys of Mount Takasaki make a fairly strenuous daily migration. A mother macaque, with a one to two pound dead infant strapped to her chest, will descend from near the top of a 1,500 foot ridge, where the animals tend to sleep to a valley near sea level where they forage on sweet potatoes and wheat that farmers leave out for them. The carrying of an infant corpse on this journey clearly “encumbers” the mothers, the authors noted, and makes foraging difficult. “This behavior is puzzling from a biological point of view,” the paper stated, “as it is a waste of energy and seems to be of no benefit to the mother.”

Another aspect of the mystery is that both older mothers and new mothers have been observed carrying dead infants, thus researchers do not believe that this is a learned behavior.

So what is happening? “Further detailed observations will be required,” the authors stated, “to analyze the exact reasons for this curious behavior.”

But one interesting point. The authors explained that this behavior is rarely observed in other animals, “because only anthropoid primates can carry the corpse of a dead infant for extended periods without using their mouth.” This makes sense, as clearly at some point an animal carrying a dead infant in its mouth will have to put down the child in order to eat. Still, other primates have been observed performing some pretty intimate acts, even with their dead infants still attached.

In a case involving geladas, baboon-like primates that live in Ethiopia and subsist primarily on grass, one mother was observed carrying her dead infant even as she began her subsequent reproductive cycle. “The female,” explained a 2011 article in WIRED, “began copulating again two weeks before abandoning the body, even carrying the smelly carcass during mating.”

The practice of infant-corpse-carrying has been reported among chimpanzees in West Africa, as well as mountain gorillas in Rwanda.

In one case from West Africa, a two and a half year-old wild chimpanzee juvenile died and its mother carried the corpse for 27 days. “Instead of decomposing, it was almost mummified,” according to the WIRED article, “as the season was very dry and hot.” This appears to be the infant-corpse-carrying record.

Yet the WIRED article raised some interesting points in cautioning us humans about overly-humanizing primate death practices.

“Chimpanzees are undoubtedly highly-intelligent, social creatures that have emotions, but what the apes in the photograph were thinking and feeling will always be a mystery to us,” the WIRED author stated, in referring to a famous 2009 National Geographic photo that appears to show a chimpanzee funeral ceremony—Digital Dying actually wrote about this photograph.

“The context of the photo made it easy to believe that they were in mourning,” the article explained. But, the paper continued, “to say that the chimpanzees were grieving, or were somber witnesses to a chimpanzee funeral, says more about what we wish to see than what is clearly visible.”

Perhaps the same can be said for infant-corpse-carrying.

Either way, a big thanks to Dr Takafumi Ishida for passing along the paper!