Political Assassinations Among Chimpanzees?

On January 7, 1974, six adult chimpanzee males of the Kasakela community in Gombe National Park, Tanzania, attacked as a gang against a lone male from the neighboring Kahama community.  Although the victim was still alive when his attackers left, he was never seen again, and so he was presumed to have died.  One month later, another gang of six Kasakela males brutally attacked another lone male from the Kahama community, who also disappeared and was presumed dead.  Over a period of three years, such attacks led to the extinction of the Kahama community, and the Kasakela community took over the territory of the Kahama community.

When Jane Goodall first reported this violent warfare between two chimpanzee communities, it shocked the world, because Goodall had previously reported that chimpanzees were peaceful--indeed, much more peaceful than human beings.  After years of studying this intercommunity warfare at Gombe, Goodall concluded that this was evidence for an instinctive propensity to warfare in the primate species that is the closest living evolutionary relative of human beings, and thus suggests the possibility that such warfare is an inherited propensity for human beings.  Richard Wrangham, Michael Wilson, and others have elaborated this "chimpanzee model" for explaining the evolution of warfare among human ancestors.

Goodall's observations of chimpanzee intercommunity violence have now been confirmed by similar observations from many chimpanzee communities across Africa.  What is most surprising about this is that lethal violence within chimpanzee communities is extremely rare (Newton-Fisher and Emery Thompson 2012).  Chimpanzees often become aggressive in conflicts with one another, but they usually resolve their conflicts without physical contact; and even if there is some physical violence, it is almost never lethal, even though chimpanzee canines are powerful weapons for wounding and killing victims.  Most aggression between adult males consists of bluffing attacks without physical contact--threatening gestures and vocalizations and charging displays.  (This is also true for human beings, who often engage in bluffing displays of aggression, but for whom homicide is rare, despite the publicity given to homicidal violence.)

After decades of observations of chimpanzee communities across Africa, there have been only four documented cases of lethal violence between adult males of the same community, in which a coalitional gang of adult males killed a lone victim.  Kaburu et al. (2013) point out that the individuals killed in these cases were either low-ranking males or they were previously deposed alpha males.

In the revised edition of his Chimpanzee Politics, Frans de Waal reported that in the summer of 1980, Luit--the alpha male of the chimpanzee community in the Arnhem Zoo in the Netherlands--was attacked brutally and killed by Nikkie and Yeroen, who had previously been alpha males (de Waal 1998, 211-214).  De Waal describes the bloody scene: "Apart from bitting off fingers and toes and causing deep gashes everywhere, the two aggressors removed Luit's testicles, which were found on the cage floor."  This looks like a political assassination.  But it's hard to know whether this case of lethal violence among captive chimpanzees is an abnormal consequence of their captive conditions.  The killing of Luit occurred at night, when the chimps were confined in their night cages.

Kaburu et al. claim to report the first case of lethal violence among wild chimpanzees in which the victim was the incumbent alpha male.  PM was the alpha male of the M-group of chimpanzees in the Malale Mountains National Park in Tanzania when he was killed on October 2, 2011.  He had been the alpha male since 2007.  After a bloody fight between PM and PR, the beta male, PR left.  A weakened PM  was then attacked brutally by a coalition of four other adult males, including two former alpha males (AL and DE).  AL was the alpha male overthrown by PM in 2007.  After the killing, there was a period of social instability.  AL became the alpha male for a short time.  But by November, PR had become the alpha male and is now the alpha male of the M-group.

Kaburu et al. explain this as an opportunistic attempt by AL (the third ranking of 10 adult males) to seize the alpha position once he saw that PM was weakened by the fight with PR, although AL was unable to hold his alpha position for long against the challenge of PR.

When I asked Michael Wilson (a primatologist at the University of Minnesota) about whether there were any other cases of alpha males being killed, he mentioned two cases at Gombe.  Vincent was the alpha male of the Mitumba community at Gombe.  He fell from a tree and severely injured himself.  He lived for another three months before two adult males attacked and killed him.  Michael says he has not yet written a report of this case.

The second case was that of Goblin, another alpha male at Gombe.  He was severely attacked and would have died if a vet had not treated his wounds.  Kaburu et al. mention this case, but they claim that Goblin had been deposed from his alpha position before the attack.

I would like to know more about how common the killing of alpha males might be for chimpanzees and how this compares with the history of political assassinations among human beings.

REFERENCES

de Waal, Frans. 1998. Chiampanzee Politics. Revised edition. Baltimore: Johns Hopkins University Press.

Kaburu, Stefano S. K., Sana Inoue, and Nicholas E. Newton-Fisher. 2013. "Death of the Alpha: Within-Community Lethal Violence Among Chimpanzees of the Mahale Mountains National Park." American Journal of Primatology 75:789-797.

Newton-Fisher, Nicholas e. and Melissa Emery Thompson. 2012. "Comparative Evolutionary Perspectives on Violence." In The Oxford Handbook of Evolutionary Perspectives on Violence, Homicide, and War, 41-60. Eds.Todd K. Shackelford and Viviana A. Weekes-Shackelford. Oxford: Oxford University Press.

Some of my posts on chimpanzee politics can be found here, here, here, here, here, and here.