NEWS - “Your enemy is our enemy” is a motto as old as the existence of animals on earth, and new research suggests it first occurred in big primates at least 5-6 million years ago. A perceived out-group threat can increase in-group cohesion.
%20moderate%20out-group%20threats%20while%20maintaining%20in-group%20cohesion.webp "Bonobos (Pan paniscus) moderate out-group threats while maintaining in-group cohesion")
Scientists have long known the mechanisms that increase in-group cohesion in societies shaped by out-group threat. However, the distribution and selection history of this association with intergroup relationships have varied across species.
In the face of threat from other groups, humans (Homo sapiens), chimpanzees (Pan troglodytes), and a number of other species draw closer together in their own groups. Since Charles Darwin, the link between out-group threat and in-group cohesion has been thought to be an adaptation to group-based competition.
Over the years, studies ranging from chimpanzees to mongooses have found evidence to support this view, but the crucial question remains: what about species without strong inter-group competition?
James Brooks of Kyoto University and an international team set up an experiment that closely mirrors previous studies in chimpanzees, using a sample of eight groups (N = 43 individuals) to test whether bonobos (Pan paniscus), which are notoriously peaceful, exhibit more affiliative in-group behavior following distant vocalizations from unfamiliar males.
"Without lethal intragroup competition, the link between in-group cohesion and out-group competition would not be adaptive, but if the effect predates the human-chimpanzee-bonobo evolutionary divergence, then it may still have traces in modern bonobos," Brooks says.
Bonobos were alert and attentive to vocalizations from other groups, but showed little increase in affiliation with their own group compared to chimpanzees. Bonobos sat upright more and rested less, with little reinforcement of social bonds.
The pan-Homo ancestors that lived 5-6 million years ago may have experienced group-based conflict, but as its intensity declined in bonobo evolutionary history, its effects became less intense and it was overcome, not just at the individual level but at the species level.
All ape species including gorillas, orangutans, chimpanzees, gibbons and humans have been observed killing each other in the wild. Bonobos may have found a way to end the pattern, not just to stop the lethal aggression, but more importantly, at some point in the last few million years, to somehow stop it.
"Humans are capable of both. We can do terrible things to people we perceive as outgroups, but we are also capable of collaborating and cooperating across boundaries," says Shinya Yamamoto of Kyoto University.
Bonobos show that how our ancestors treated other groups did not determine the fate of our descendants. Our species shares elements of both chimpanzee and bonobo group relationships. Yamamoto says it is important to understand how both have evolved.
Original research
Brooks J, van Heijst K, Epping A, Lee SH, Niksarli A, Pope A, et al. (2024) Increased alertness and moderate ingroup cohesion in bonobos’ response to outgroup cues. PLoS ONE 19(8): e0307975. DOI:10.1371/journal.pone.0307975
%20moderate%20out-group%20threats%20while%20maintaining%20in-group%20cohesion.webp "Bonobos (Pan paniscus) moderate out-group threats while maintaining in-group cohesion")
Scientists have long known the mechanisms that increase in-group cohesion in societies shaped by out-group threat. However, the distribution and selection history of this association with intergroup relationships have varied across species.
In the face of threat from other groups, humans (Homo sapiens), chimpanzees (Pan troglodytes), and a number of other species draw closer together in their own groups. Since Charles Darwin, the link between out-group threat and in-group cohesion has been thought to be an adaptation to group-based competition.
Over the years, studies ranging from chimpanzees to mongooses have found evidence to support this view, but the crucial question remains: what about species without strong inter-group competition?
James Brooks of Kyoto University and an international team set up an experiment that closely mirrors previous studies in chimpanzees, using a sample of eight groups (N = 43 individuals) to test whether bonobos (Pan paniscus), which are notoriously peaceful, exhibit more affiliative in-group behavior following distant vocalizations from unfamiliar males.
"Without lethal intragroup competition, the link between in-group cohesion and out-group competition would not be adaptive, but if the effect predates the human-chimpanzee-bonobo evolutionary divergence, then it may still have traces in modern bonobos," Brooks says.
Bonobos were alert and attentive to vocalizations from other groups, but showed little increase in affiliation with their own group compared to chimpanzees. Bonobos sat upright more and rested less, with little reinforcement of social bonds.
The pan-Homo ancestors that lived 5-6 million years ago may have experienced group-based conflict, but as its intensity declined in bonobo evolutionary history, its effects became less intense and it was overcome, not just at the individual level but at the species level.
All ape species including gorillas, orangutans, chimpanzees, gibbons and humans have been observed killing each other in the wild. Bonobos may have found a way to end the pattern, not just to stop the lethal aggression, but more importantly, at some point in the last few million years, to somehow stop it.
"Humans are capable of both. We can do terrible things to people we perceive as outgroups, but we are also capable of collaborating and cooperating across boundaries," says Shinya Yamamoto of Kyoto University.
Bonobos show that how our ancestors treated other groups did not determine the fate of our descendants. Our species shares elements of both chimpanzee and bonobo group relationships. Yamamoto says it is important to understand how both have evolved.
Original research
Brooks J, van Heijst K, Epping A, Lee SH, Niksarli A, Pope A, et al. (2024) Increased alertness and moderate ingroup cohesion in bonobos’ response to outgroup cues. PLoS ONE 19(8): e0307975. DOI:10.1371/journal.pone.0307975