The 23-year-old chimpanzee Wouter has died in Safari Park Beekse Bergen. The monkey suffered serious injuries during a fight with others of its kind. He died on the operating table. Lethal violence is not uncommon among chimpanzees. KIJK wrote an article about it in 2015, which you can read here.
This article originally appeared in KIJK 11/2015
No one had the murder of Pimu see coming. The alpha male lived a quiet life in a chimpanzee group near Lake Tanganyika in Tanzania. The biologists who observed him in the last hours before his death saw Pimu being groomed by two females when four males suddenly burst out of the bushes and pounced on him. When the fight was over an hour later, Pimu lay lifeless on the ground, with large wounds on his face, hands and feet.
Chimpanzees are ‘born killers’
It’s not just the alpha males that have to watch out for their own kind. Researchers in Uganda watched as a group of young male chimpanzees came across two females with babies from another group and chased them until one of the young fell to the ground. The baby was beaten to death and eaten, skin and hair.
These horrific incidents are no exceptions. Murders occur regularly among chimpanzees, sometimes for no apparent reason. The big question is whether violence is part of their natural behavior. For decades, the killings have been dismissed as the excesses of “sick” individuals: monkeys that had come into contact with humans too often or had been hunted.
But a growing group of scientists believe that chimpanzees are simply “born killers.” Killing would be second nature for the animals to increase their chances of survival. According to these researchers, there are even lessons for humans to learn from violence, since we are related to chimpanzees.
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Torn off genitals
The American primatologist Michael Wilson published the largest study to chimpanzee violence ever. The University of Minnesota researcher, with the help of dozens of colleagues in the field, collected data on 152 cases of lethal violence between the monkeys.
“The murders are happening everywhere; they have been observed in seventeen of the eighteen chimpanzee populations under observation,” says Wilson. The murders are often accompanied by excessive violence. “Chimpanzees usually bite the victim’s throat, but they often tear off body parts with their teeth; the genitals, for example. Sometimes even parts of the body are eaten.”
Wilson carefully mapped out the circumstances of each murder case in his study. He looked at whether there was a food shortage in the area, how densely populated the monkeys’ habitat was and what the population composition was like.
But he mainly kept track of whether there was any human intrusion into the area. In the eyes of some scientists, humans are the biggest suspect in the question of guilt surrounding chimpanzee violence. The American anthropologist Robert Ferguson argued in 2011 that the continuing massacres of chimpanzees are the result of advancing cities and ever-expanding agricultural areas. According to him, the restriction of their living space increases competition for food and leads to deadly conflicts.
Eliminate competition
But Wilson found no connection between the number of fatal chimpanzee incidents and proximity to humans. In fact, most of the killings appeared to have occurred in the area where the number of human intrusions was smallest: Uganda’s Kibale National Park. He therefore suspects that the monkeys simply kill others of their kind to increase their chances of survival and reproduction. Mutual violence between animals of the same species is not unique, he emphasizes. “Lions sometimes also kill competitors or their young.”
Chimpanzees in most cases kill members of competing groups, Wilson’s study shows. “Attacking and fatally wounding invaders from other groups is likely to their advantage because it eliminates potential competitors.”
It is also striking that the murders are most often committed by males (93 percent) and that the victims are also usually male (73 percent). This indicates that many incidents have to do with ranking. “Males spend a lot of time doing that. It is likely that lower-ranking individuals sometimes forge a pact to eliminate the alpha male, as in the case of Pimu.”
Deadly confrontations
The Dutch biologist Liesbeth Sterck recognizes the image of violent males. “Male chimpanzees also have the strongest weapons,” she adds. “Their canines are longer than those of females. They can easily bite the throat of a fellow with it.”
Sterck has been researching primate behavior at the University of Utrecht for years and agrees with Wilson’s conclusions. “The study neatly lists all forms of violence among chimpanzees. And then it turns out that the presence of people has little or no influence, while the presence of many males does.”
According to her, the monkeys’ lifestyle also leads to deadly confrontations. Chimpanzees regularly travel alone or in a small group. During these trips, groups of chimpanzees sometimes come across a stray individual from another area. Observations show that the monkeys then often attack. “They apparently cannot resist the temptation and approach such an individual very quietly, as if they were hunting,” says Sterck.
Tribal conflict?
The idea that chimpanzees kill out of self-interest is not accepted for the time being by the scientists who hold humans responsible for chimpanzee violence. They believe that Wilson has not mapped out the influence of human activity on chimpanzees well enough. The American noted for each chimpanzee group whether it was fed by humans, how large the habitat was and how often local residents were spotted there. “But those factors are too simple to properly determine the impact of humans on the monkeys,” says Robert Ferguson The New York Times.
According to Wilson, his opponents are ashamed of their murderous ‘cousins’. “Chimpanzees have similar bodies, use tools and sometimes even hunt animals with spears, just like our ancestors,” he explains. “I think some scientists have the idea that you also justify killing for people if you label it as natural behavior in chimpanzees.”
According to the primatologist, this fear is unfounded. “We are distinguished from monkeys by our civilization. I dare say that in many places in the world we have succeeded in reducing the number of violent incidents in our society. That proves that we have much more self-control.”
Wilson thinks that we can learn from the violent behavior of chimpanzees. He sees the fights between monkeys from different groups as a primitive tribal struggle. “It cannot be ruled out that these types of arguments are the origins of modern warfare.”
War and peace
The idea that chimps’ murderousness and humans’ warlikeness can be traced back to the two species’ shared ancestor is consistent with several studies. For example, the German sociologist Gunnar Heinsohn discovered at the beginning of this century that violence breaks out relatively often in populations with many (young) men; just like in groups of chimpanzees. There is also evidence that hunter-gatherers in the Amazon often attack when they encounter more or less helpless individuals from other tribes.
Being on the other side not all monkeys are violent. Wilson also studied confrontations between bonobos. During all observations, only one case was recorded in which a bonobo was killed by members of its own species. The Dutch primatologist Frans de Waal is therefore not convinced of Wilson’s theory about the origins of war. “The evidence that apes are naturally violent is solid, but the claim about the origins of warfare is full of holes: you can’t just ignore the bonobo.” Evolutionarily speaking, bonobos are as close to humans as chimpanzees. “Their genome has recently been mapped,” says De Waal.
According to De Waal, archaeological evidence for the first wars between humans goes back at most 12,000 years. This corresponds to the period in which humans invented agriculture, started keeping livestock and settled permanently in certain areas. “That agricultural revolution may have been the moment when warfare arose between villages and countries. It may well be that our ape-like ancestors did not wage war at all.”
Wilson admits that more research needs to be done on his theory of war. “It’s guesswork. Perhaps chimpanzees and bonobos have a common ancestor that passed on war to only one species,” he suggests. “One primate is not the same when it comes to violence.”
Text: Dennis Rijnvis
Tags: Chimpanzees regularly kill kind
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