Note that in about 50 years of study, there were only 152 killings with which this study was concerned, 58 (38%) that were observed, 41 (27 percent) that were inferred, and 53 (35 percent) that were suspected. So, 62 percent of the killings were not actually seen. The authors also conclude that human impacts on chimpanzees are not responsible for violent behavior. The Times essay presents different points of view on the study and its conclusions (see this also).
There has only been one known chimpanzee war
I've written about nonhuman violence before, most recently in an essay called "Animals Are Not Warmongers: An Important Media Corrective" in which I wrote on a report by Colin Barras in New Scientist magazine titled "Only known chimp war reveals how societies splinter" (the print edition version is called "Secrets of the only known chimp war"). Despite media often reporting and inferring that many nonhuman animals (animals) are typically violent, this is a misrepresentation of how they really live. Robert Sussman, an anthropologist at Washington University in St. Louis, and his colleagues Paul Garber and Jim Cheverud, reported in 2005 in The American Journal of Physical Anthropology that for many nonhuman primates, more than 90 percent of their social interactions are affiliative rather than competitive or divisive (see cooperation+altriuism">here for an update on what we're learning about cooperation in other animals). Because there's only one known chimpanzee war, a point made by Duke University's Joseph Feldblum who, with a number of colleagues, analyzed this unique event, claiming we inherited our widespread destructive behavior from "them" is not a credible conclusion.