Chimpanzees are highly intelligent primates that live in sophisticated, fission-fusion societies, exhibiting behaviors like cooperative hunting, tool use, and strong social bonds. However, their social life also contains a darker element: the consumption of their own species. Cannibalism is documented across several wild populations, occurring in distinct, context-dependent situations.
The Reality of Chimpanzee Cannibalism
Observed instances of chimpanzee cannibalism are rare but documented in long-term study sites across Africa, including Gombe, Mahale, Budongo, and Taï. This behavior is not a regular part of the chimpanzee diet, which primarily consists of fruit, leaves, and insects, supplemented by hunting monkeys or small antelopes. Consumption most often involves infants and is categorized based on whether the victim was killed or found already deceased.
The act of consumption is often partial, especially following an aggressive event, but it is consistent in certain contexts. In communities like Kibale, consuming a victim after a successful infanticide is considered the norm. Researchers distinguish between the killing, usually driven by social or territorial motives, and the subsequent consumption, which adds a nutritional component.
Behavioral Drivers: Infanticide and Intergroup Predation
The most frequently observed aggressive form of cannibalism is linked to infanticide, particularly within-group killings committed by adult males. This behavior is supported by the sexual selection hypothesis: males kill unrelated infants to hasten the mother’s return to fertility. A female whose infant is lost to infanticide may conceive approximately seven times faster than if the infant had survived the full nursing period.
This strategy increases the male’s reproductive success by creating an immediate mating opportunity. Documented cases show adult males snatching and cannibalizing newborns immediately after birth. This suggests that expectant mothers taking a “maternity leave” from the group to give birth alone may be a counterstrategy against the high risk of infanticide.
Cannibalism also follows lethal aggression during territorial battles between different chimpanzee communities. Intergroup conflicts involve coordinated patrols by males who sometimes lethally attack a chimpanzee from a neighboring group. The consumption of the remains by the attackers has been observed following the death of an adult or juvenile.
Consuming the body serves a dual purpose: it is a potent display of territorial dominance against rivals, and it provides a source of protein. However, the primary motivation for the attack is the elimination of rivals and the expansion or defense of territory, with consumption being a secondary outcome.
Opportunistic and Scavenging Consumption
A distinct category of cannibalism involves the consumption of an individual who was not killed by the consumer. This behavior is categorized as opportunistic or scavenging consumption and usually involves infants who died from natural causes, stillbirths, or those abandoned after death. Unlike aggressive incidents, this form appears driven by nutritional need or simple opportunity, often occurring in a non-aggressive context.
Maternal cannibalism, where a mother consumes her own infant, is extremely rare in chimpanzees compared to other animal species. In the few documented cases, the infants were often stillborn or died shortly after birth, and the mother did not appear ill. Researchers suggest that the strong mother-infant bond typical of chimpanzees likely prevents this behavior in most circumstances.
When a mother consumes a deceased infant, she may share the remains with other group members, treating the corpse similarly to meat from a successful hunt. This scavenging behavior highlights that chimpanzees will consume the remains of a deceased conspecific if the opportunity arises and there is a nutritional benefit.