A new study in Nature states that chimpanzees have warrior-like instincts on their own, and aren't more likely to get aggressive when humans are around.
Researchers looked at data from more than 50 years in 18 different chimpanzee communities, as well as data from four groups of bonobos, the kinder cousin of the chimpanzee. The data showed that killings between chimps are not more likely to happen when humans are somehow involved in their life, and bonobos do not kill each other, period.
Chimpanzees and humans share a common ancestor from about seven million years ago, which is why researchers are so fascinated by whether or not there is a link between chimp and human behavior. Michael Wilson, an evolutionary anthropologist at the University of Minnesota, says that although people often argue that combat between humans is caused by factors like the development of weapons and the start of agriculture, chimp behavior seems to suggest that warfare has "a long evolutionary history."