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Chimpanzees' 'Lethal Aggression' is a Natural Trait and is not Influenced by Human Activity

An analysis of chimpanzee behaviour, using data from 22 different communities, has shown that chimpanzee aggression, including organised killings, is not influenced by human activity, but stems from natural, evolved tendencies.

A group of male chimpanzees listening to the communications of a neighbouring group. Photo: John Mitani.

A group of male chimpanzees listening to the communications of a neighbouring group. Photo: John Mitani.

Chimpanzees display violent behaviour within and between communities, an observation known for some decades but with long-standing and opposing explanations.

One explanation describes chimp violence as being a by-product of human activity. Neighbouring humans can compete with chimpanzees for food and space, limiting the resources available to the chimps.  This theory suggests that human induced resource limitation puts strains on chimpanzee social bonds thus drawing out violent tendencies that wouldn’t otherwise manifest.

An alternative theory suggests that chimpanzee violence is an adaptive trait, evolved to promote chimpanzee survival and reproductive success just like any other characteristic. Through the violence exhibited by chimpanzees, individuals can secure more territory from rival groups, more food from rival chimps, and more offspring from rival suitors.

When I mention ‘chimpanzee’, by the way, I am referring to the common chimpanzeePan troglodytes. There are actually two species of chimpanzee: the common chimp and the pygmy chimp, or bonobo. In the 2 million years since these species split in the evolutionary tree, they have developed substantially different social structures. The more well-known species, the common chimpanzee (which I’ll continue to call ‘chimpanzee’), has a more male dominant society and is the more violent of the two species.

The present study analysed chimp-chimp killings from 18 chimpanzee communities and 4 bonobo communities using data collected over 50 years. The primatologists then compiled data on the degrees of human disturbance in these communities, comparing chimp killings with exposure to human activity. There was no correlation between the two, i.e. humans did not influence the incidence of violence amongst chimpanzee groups.

Almost all recorded killings were from the common chimpanzee, mostly males (92%) killing males (73% of victims). Though this was a study of violence in the genus Pan, the numbers are interesting to compare with Homo sapiens. In the United States between 1980 and 2008, 90% of murderers were male, and 77% of victims were male.

Though the adaptive benefits of chimpanzee violence are plentiful, violence is not the only way. Out of the 153 killings included in this study, just one was committed by a bonobo. And since us humans are equally related to both the common chimp and bonobo, this study is no reflection on human nature.

In conclusion, humans might occasionally get primates drunk or give them assault rifles*, but it seems that lethal aggression is not our fault, but has instead evolved in the common chimpanzee lineage because of its varied benefits for their fitness.

 *Promo for ‘Rise of the Planet of the Apes’

Originally published on Think Inc.

Story source: ScienceAlert

Research paper: Michael L. Wilson, Christophe Boesch, Barbara Fruth, Takeshi Furuichi, Ian C. Gilby, Chie Hashimoto, Catherine L. Hobaiter, Gottfried Hohmann, Noriko Itoh, Kathelijne Koops, Julia N. Lloyd, Tetsuro Matsuzawa, John C. Mitani, Deus C. Mjungu, David Morgan, Martin N. Muller, Roger Mundry, Michio Nakamura, Jill Pruetz, Anne E. Pusey, Julia Riedel, Crickette Sanz, Anne M. Schel, Nicole Simmons, Michel Waller, David P. Watts, Frances White, Roman M. Wittig, Klaus Zuberbühler, Richard W. Wrangham. Lethal aggression in Pan is better explained by adaptive strategies than human impactsNature, 2014; 513 (7518): 414 DOI: 10.1038/nature13727