UT researchers found the largest known group of wild chimpanzees has permanently split into two, according to an April 9 study published in the journal “Science.”
The study documents the split of the Ngogo chimpanzees, a community of wild chimpanzees in Kibale National Park in Uganda, that have been documented for over 30 years. Two clusters within the community — the Western cluster and the Central cluster — began undergoing group polarization in 2015. Complete fission and violence started in 2018, according to the study. Genetic evidence suggests that chimpanzee community fissions happen once every 500 years, according to the study.
The clusters interact in a “fission-fusion” dynamic, where the chimps will intermingle with members from other clusters, Aaron Sandel, associate professor of anthropology and lead researcher of the study, said. Today, the communities’ Western and Central clusters are spatially separated, he said.
Sandel said observing polarization among the chimps can offer hypotheses to test human behaviors.
“I think a deeper understanding of some of the parallels between humans and chimps could potentially change the way we relate to ourselves and resolve conflicts,” Sandel said.
Researchers followed chimpanzees, recording their proximity and affiliations to one another, according to the study. Isabelle Clark, an anthropology doctoral candidate at UT who worked on the study, said that systematic data collection methods allow researchers to remain objective while documenting the chimpanzees. One such method was using pre-defined behaviors, like grooming and aggression, that researchers agree on.
“You’re just trying to do your best to capture as much as you can,” Clark said. “You’re surrounded by potentially dozens of chimpanzees, all screaming, running around, tearing through the vegetation.”
Sandel pointed to an incident in June 2015 as the first sign of group division. When chimps from the Central and Western communities met, rather than uniting in typical fission-fusion fashion, the Central chimpanzees chased the Western ones away, he said.
The Western cluster conducted the first territorial patrol against the central cluster in 2016, and territorial patrols conducted by both clusters increased through 2018, according to the study. The Western cluster conducted the first lethal attack against the Central cluster in January 2018, killing a young adult male, Sandel said. At least six adult males and 14 infants have since been killed, with the Western cluster initiating the attacks, according to the study.
Sandel said social and demographic changes, like the death of five adult chimps in 2014, a change in the community’s alpha male chimp in 2015 and a disease outbreak that killed 25 in 2017, may have contributed to group division.
Blessing Asianzu, an anthropology PhD student and researcher on the project, said seeing the conflict among the chimpanzees can challenge people to understand their conflicts through an interpersonal lens.
“I think that what’s happening with the chimps is a challenge to humans,” Asianzu said. “A lot of times we like to hide behind the frames of, ‘Oh, I belong to this tribe, or I belong to this ethnic group or I belong to this political group,’ when, in actual sense, some of the conflicts that we are actually fighting are conflicts that are relational.”
