Few actions orchestrated in the animal kingdom are awarded a headline that would befit mankind. The chimpanzee, however, is the exception.
“Chimp leader assassinated by gang of underlings,” read the headline last year in New Scientist. It told the story of Pimu, who led his cohort of chimpanzees until a violent day in March last year when Pimu picked the wrong fight. Four chimpanzees appeared out of nowhere, according to New Scientist, and beat Pimu to death with their hands and feet. It was a grisly end for a species that, along with humans, are among the only animals to coordinate attacks on their own kind.
But such a murder was a natural action, according to a study published Wednesday in Nature. The paper, which analyzed data from 426 combined years of observation and 18 separate chimp sites, argues chimps are not driven to violence by their contacts with humans, which some scientists have previously contended. Chimps, rather, are natural born killers.
“Variation in killing rates was unrelated to measures of human impacts,” said the paper, which was researched by an international team of 30 scientists. “… The adaptive strategies hypothesis views killing as an evolved tactic by which killers tend to increase their fitness through increased access to territory, food, mates and other benefits.”
The research feeds into a lengthy debate over the nature of chimp violence, and what it means for humanity’s own propensity for murder. “We’re trying to make inferences about human evolution,” lead researcher Michael L. Wilson, an anthropologist at the University of Minnesota, told the New York Times. Even in areas where humanity’s hand and habitat loss were not discernible, the chimps conveyed the same bellicosity, the research found. It signified that competition over resources — even when abundant — drove the chimp wars.
The findings: Among 152 killings, males were the aggressors 92 percent of the time, and the victims 73 percent of the time. Most of the killings were “intercommunity attacks,” meaning that a gang of chimps would gang up on one. The average ratio? Eight to one.
“Chimpanzees often fragment into temporary parties that travel and forage independently within their community’s home range,” wrote anthropologist Joan Silk in an accompanying article. “When parties of males encounter single individuals from other communities, they sometimes launch brutal assaults that leave victims gravely wounded or dead.”
The fact that chimps kill is agreed upon. They’re sometimes even violent against humans. In the mid-1990s, one chimp named Saddam roamed remote villages of Uganda, targeting people. He was named for the Iraqi dictator Saddam Hussein, reported a New York Times Magazine article published last year. “One victim was grabbed from a blanket as her mother was picking millet nearby. Saddam later pulled a small child off the back of a woman digging into a cassava field. He grew bolder, and by the summer of 1998, he had attacked seven children, killing at least two of them.”
But the question remained: Why are chimps violent? One early study reported that after researchers fed bananas to chimps in 1962 at the Gombe National Park in Tanzania, the primates began attacking each other. After the bananas stopped, so did the violence. It led “some researchers to conclude that these killings were the consequence of human intervention,” Silk wrote.
The rate of killing, rather, seems more dependent on how many males were in each band of chimps as well as population density. It’s inter-community tension — not outer-community tension.
Just as chimps appear to reflect some humanity’s better traits, they also reflect the bad, Silk wrote.
“The behavior of non-human primates, particularly chimpanzees, are often distorted by ideology and anthropomorphism, which produce a predisposition to believe that morally desirable features, such as empathy and altruism, have deep evolutionary roots, whereas undesirable features, such as group-level violence and sexual coercion, do not,” she wrote. “This reflects a naive form of biological determinism.”