Chimpanzees unite against a common enemy

In the face of threats from other groups, humans become more cohesive and cooperative with their own, an association that Charles Darwin said could be an evolved ability. Today, a research group from Kyoto University has experimentally demonstrated for the first time that this propensity is shared with chimpanzees, one of our closest relatives.

“Despite the importance of understanding how humans can cooperate with their group and continue to commit acts of extreme aggression outside the group, there have so far been few studies on whether the association between these behaviors is valid in non-human primates ”. says first author James Brooks.

Drawing on field research that suggested chimpanzees were more cohesive on the days and months they had out-of-group encounters, the team tested the direct relationship between out-of-group threat and cohesion within the group. by simulating an out-of-group meeting and observing the subjects. behaviour.

Five groups of chimpanzees listened to vocalizations of unknown individuals, as well as a check of crow vocalizations. The team found that subjects who heard out-of-groups became more alert and stressed, but instead of translating this into tension within the group, the chimpanzees grew closer to each other, engaged in more affiliated behaviors. and were less aggressive when given little food. compared to the control group.

This suggests that in chimpanzees, as well as in humans, competition between groups promotes cohesion, and further that intergroup competition in human evolution may have led to our ability to maintain cooperative and tolerant relationships in de large groups in the presence of a common enemy.

“This is the first experimental evidence that humans share this propensity with chimpanzees,” explains study supervisor Shinya Yamamoto, “but it remains to be tested whether this is due to the strong evolutionary history of the two species of intergroup competition. or to a more common trait shared with other great apes. “

The team is currently investigating whether the same pattern is seen in bonobos – the other closest relatives of humans – who are known not to commit fatal assault outside of the group.

The study “Uniting against a common enemy: the threat of outgroups promotes in-group cohesion in chimpanzees” will appear on February 24, 2021 in the journal PLOS ONE.