Murder comes naturally to Chimpanzees

The concept of murder is thought of as a uniquely anthropological trait. Death in the animal kingdom is rife, but seldom is it without direct need. This need is usually either for food or to eliminate rival competition. Lions, for example, are known to regularly commit infanticide if another male sired the young of their partner. However it is only humans, and our most closely related ape, the chimpanzee, which will gang up on others of the same species and deliberately eliminate them. Until now there has been debate around whether or not murder in chimpanzees is an adaptive trait, or has come about through human influence. It has been hypothesized that human impact increases the aggression of chimpanzees through activities such as deforestation, disease introduction, hunting and giving of food. However this hypothesis has been found to lack supporting evidence, with the alternative becoming much more widely accepted.

A paper published last year in Nature by Wilson et al. looked at the killings associated with chimpanzee (Pan troglodytes) and bonobo (Pan paniscus) populations over a 5-decade period. 152 killings by chimpanzees were observed, with only 1 by bonobos. 92% of the attackers were male, and 73% of the victims the same. 66% of the killings that took place between rival groups, and, perhaps most importantly, the median ratio of attacker to victim of 8:1. This is very reminiscent of gang collaboration in human killings. The sole bonobo killing is reflective of the idea that they are less violent than their chimp cousins.

These results support the hypotheses that murder has become adaptively beneficial to chimps, and whilst this is not the first paper to support this, it is the first to test the two conflicting hypotheses within the same environment. It now seems very likely that murder helps chimpanzees to succeed in life.

A link to original paper can be found at :http://www.nature.com/articles/nature13727.epdf?referrer_access_token=ElhlhDVf-yYLmiXWt-XSFtRgN0jAjWel9jnR3ZoTv0NpG5ubYJPB-kwLr549EZvXYPpUc__-dtTkQd7PyXLDqL5SCYRQO09IRyq5QHhQMwxJwdEdGuuPPM9t3kFL8yoF

References

Wilson, M., Boesch, C., Fruth, B., Furuichi, T., Gilby, I., Hashimoto, C., Hobaiter, C., Hohmann, G., Itoh, N., Koops, K., Lloyd, J., Matsuzawa, T., Mitani, J., Mjungu, D., Morgan, D., Muller, M., Mundry, R., Nakamura, M., Pruetz, J., Pusey, A., Riedel, J., Sanz, C., Schel, A., Simmons, N., Waller, M., Watts, D., White, F., Wittig, R., Zuberbühler, K. and Wrangham, R. (2014). Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature, 513(7518), pp.414-417.

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Jamie Graham

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