Why are monkeys always aggressive

Brutal desecration of corpses of chimpanzees

Surprisingly brutal: In the tree savannah of Senegal, chimpanzees apparently killed a former group member and continued to attack his corpse for hours afterwards. Especially the males of the squad were surprisingly aggressive towards the former leader of the squad. Even fatal violence between members of a chimpanzee group is extremely rare. The subsequent abuse of the corpse is even more unusual, the researchers report.

Great apes can become aggressive. This is evidenced by chimpanzees who attack rivals, hunt other monkeys together or take action against competing groups. However, severe aggression or even fatal attacks by members of a squad among themselves are extremely rare in the primates. "Most of the violence occurs between groups," says Jill Pruetz of Iowa State University.

What the anthropologist and her colleagues observed in Fongoli in Senegal in 2013 shocked even the experts: “It was cruel to watch and at first I didn't understand what was happening. I never expected the chimpanzees to be so aggressive with their bodies, ”reports Pruetz. What happened?

Aggressive desecration of corpses

When the scientists arrived at their research facility that day, they saw the lifeless body of a former group member lying on the floor: the chimpanzee Foudouko had once been the leader of the group, but had lived in exile for the last few years and only occasionally with them interacts with other chimpanzees in the group.

The desecration of the former group member was completely unexpected for the researchers. © Iowa State University

Now he was dead - and was brutally attacked by his former companions. For almost four hours, the chimpanzees repeatedly beat the body, attacked it and even displayed cannibalistic behavior. The young male chimpanzees were the most aggressive, as the team now reports. Overall, however, the entire group participated in the attack - only two of Foudouko's formerly closest allies showed no aggression.

Competitor switched off?

But what was the reason for this strange behavior? Certainly not mourning, says Pruetz. She even suspects that the group was to blame for Foudouko's death and killed him. "Chimpanzees are very social beings and it seems that Foudouko tried to be fully re-accepted into the group," says the scientist.

Could it be that the other males felt threatened and eliminated a possible competitor? In fact, the fight for females among the Fongoli chimpanzees is tough. Because there are more male than female monkeys in the area. Man could be to blame for the gender imbalance: Native residents hunt female primates to get young animals for trade. However, catching one every few years can have a huge impact, as chimpanzees rarely reproduce and tend to their offspring for a long time.

Disruptive human factor

Pruetz has long suspected man-made changes that disrupt the habitat and way of life of animals as the cause of aggression among conspecifics. Whether this was really the case with Foudouko is not certain, but it is not unlikely, the researchers write.

“Aside from humans, few animals show such deadly aggression. Experts have long argued about what triggers this violent behavior among primates, ”says Pruetz. It is important to understand this behavior - also because chimpanzees are acutely threatened with extinction anyway.

Foudoko's body buried Pruetz and her colleagues after the rest of the group disappeared. However, he is to be exhumed again later. The researchers then hope to be able to find out more about the cause of death. (International Journal of Primatology, 2017)

(Iowa State University, Feb 6, 2017 - DAL)

February 6, 2017