Lethal aggression in pan troglodyte, or, Killer Chimps!

In homo sapiens, males account for 90% of the perpetrators of homicide, and 77% of victims (FBI data). The percentages for chimpanzees/bonobos are 92% and 73%. Maybe that Darwin fellow was onto something.

Lethal aggression in Pan is better explained by adaptive strategies than human impacts

• 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
• et al.

• Affiliations
• Contributions
• Corresponding author

Nature

 

513,

 

414–417

 

(18 September 2014)

 

doi:10.1038/nature13727

Received

 

03 March 2014 

Accepted

 

04 August 2014 

Published online

 

17 September 2014

Observations of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) provide valuable comparative data for understanding the significance of conspecific killing. Two kinds of hypothesis have been proposed. Lethal violence is sometimes concluded to be the result of adaptive strategies, such that killers ultimately gain fitness benefits by increasing their access to resources such as food or mates^{1, 2, 3, 4, 5}. Alternatively, it could be a non-adaptive result of human impacts, such as habitat change or food provisioning^{6, 7, 8, 9}. To discriminate between these hypotheses we compiled information from 18 chimpanzee communities and 4 bonobo communities studied over five decades. Our data include 152 killings (n = 58 observed, 41 inferred, and 53 suspected killings) by chimpanzees in 15 communities and one suspected killing by bonobos. We found that males were the most frequent attackers (92% of participants) and victims (73%); most killings (66%) involved intercommunity attacks; and attackers greatly outnumbered their victims (median 8:1 ratio). Variation in killing rates was unrelated to measures of human impacts. Our results are compatible with previously proposed adaptive explanations for killing by chimpanzees, whereas the human impact hypothesis is not supported.