Chimps have been spotted killing and then eating their former tyrannical leader.

Jill Pruetz, an professor of anthropology, said that she found it "very difficult and quite gruesome to watch" the group of chimpanzees kill a member of their own community and then abuse the animal's dead body.

Professor Pruetz has described how she saw a group of the animals discover the body of a chimp called Foudouko, a former leader of the Fongoli community who had since been exiled for five years and who was probably killed by members of the group. After they came across the dead body, they abused and ate it for nearly four hours, the Iowa State University anthropologist described.

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Scientists still aren't sure why the chimps exhibited such strange and disturbing behaviour, and finding out may help show why few animals apart from humans show such deadly aggression and help answer questions about why chimps are going extinct. It's likely that man-made environmental changes have disrupted the chimp's environment and led them to be upset, and competition for a mate and a power struggle with younger chimps might also be responsible for his death.

Even the fact that Foudouko was able to survive in isolation for so long is rare, according to the scientists. No chimp has been recorded living on their own for so long, and scientists watched as he trailed the group from a distance and sometimes privately interacted with his allies.

But the chimp's downfall may have come from an attempt to make his way "back into the social group", according to Professor Pruetz. If he was more submissive he may have stood a chance, but he was probaly killed because of his aggression, they said.

The young chimps – who were most aggressive in their abuse of the body – may have felt that they were under threat from Foudouko, who was very dominant and widely feared when he was a leader. Since those younger animals were larger in number and more physically fit, they were able to get rid of Foudouko by killing him in front of his allies.

But even once Foudouko was dead, it was clear that the other chimps were still afraid, said Professor Pruetz. If his body would move or jerk during the attacks they would react in fear, for instance.