Chimpanzees and gorillas, two different great ape species thought to have split from a shared ancestor about 8 million years ago, are known to peacefully coexist in some regions, sharing food and shelter resources, and even playing together, with little to no conflict.
But in 2019, that notion was challenged when researchers observed chimps killing gorillas in the wild for the first time in two separate encounters.
“At first, we only noticed screams of chimpanzees and thought we were observing a typical encounter between individuals of neighboring chimpanzee communities,” study first author Lara Southern, a Ph.D. student at the Max Planck Institute for Evolutionary Anthropology in Germany, said in a statement.
“But then, we heard chest beats.”
The first lethal skirmish involved 27 chimps and just five gorillas. A camera hidden behind trees of the Loango National Park in Gabon, Africa, revealed a gang of excited chimps emitting deafening screams as they attack the gorillas for 52 minutes. The encounter left three chimps injured and one gorilla infant dead.
The second confrontation lasted over an hour, involving seven gorillas and 27 chimps, all of which were left unscathed. Yet another gorilla infant was killed. This time, however, the chimps ate the victim, nearly leaving only a naked skeleton.
Chimpanzees are omnivores, meaning they eat both plants and animals. They are also known to be hotheads within their own species — at least until now. By age 5, they are stronger than most human adults.
“Considering that female western gorillas can be almost twice the weight of a typical 100-pound male chimpanzee, while male gorillas can be three to four times as heavy as a male chimpanzee, the fact that chimpanzees can steal an infant gorilla from its mother is remarkable,” Richard Wrangham, an evolutionary biologist at Harvard University who was not involved in the study, told Gizmodo.
“Chimpanzees clearly revel in hunting and killing other primates, from monkeys to chimpanzees and even humans (mostly infants). Bonobos too kill various other species for meat, and there are even a few observations of their stealing infant monkeys away from their distraught mothers and then carrying them around, apparently to play with, until they died,” Wrangham said.
“Gorillas, by contrast, show very little interest in killing other species, whether in the wild or captivity.”
So, why all the fuss?
Researchers have two main theories to explain the lethal attacks: predation or competition, the latter of which may be triggered by climate change.
“It could be that sharing of food resources by chimpanzees, gorillas and forest elephants in the Loango National Park results in increased competition and sometimes even in lethal interactions between the two great ape species,” said Tobias Deschner, co-leader of the Loango Chimpanzee Project since 2005 and a primatologist at the Max Planck Institute for Evolutionary Anthropology.
But climate change could be complicating hunts for food. Researchers say changes in temperatures and other climate factors are causing “a collapse in fruit availability” in the tropical forests of Gabon.
“We are only at the beginning to understand the effects of competition on interactions between the two great ape species in Loango,” study co-author Simone Pika, a cognitive biologist at Osnabrück University in Germany and co-leader of the Loango Chimpanzee Project, said in the statement. “Our study shows that there is still a lot to explore and discover about our closest living relatives, and that Loango National Park with its unique mosaic habitat is a unique place to do so.”
The study was published Monday in the journal Scientific Reports.