Study Documents First Observed Civil War Among Wild Chimpanzees in Uganda

A new study published in the journal Science details the first observed instance of civil war among wild chimpanzees. The conflict occurred within the Ngogo chimpanzee community, the largest known group of its kind, located in Uganda's Kibale National Park. Observations spanning more than three decades revealed a permanent split in the group, resulting in sustained inter-group violence.

The Ngogo chimpanzees had maintained social cohesion from at least 1995 until 2015. In 2015, the group divided into two distinct factions: the western group and the central group. This division led to 24 coordinated attacks by the western group on the central group over the following seven years, from 2015 to 2022.

The attacks resulted in the deaths of at least seven adult males and 17 infants in the central group.

The western group's actions reduced the central group's survivorship to the lowest level ever documented in a wild chimpanzee community. Researchers attribute the violence to shifts in group identities and dynamics, drawing parallels to human civil conflicts.

Primatologist Aaron Sandel, who observed early signs of tension in June 2015, noted nervous behaviors among chimpanzees as subgroups approached each other.

Earlier that day, the group's alpha male had submitted to another chimpanzee, signaling a change in hierarchy. The deaths of several key older individuals in the years prior weakened social connections across neighborhoods. A disease outbreak in 2017 further contributed to the split.

This event likely expedited the polarization within the group. The study suggests that such disruptions in social structure can lead to organized aggression. > "Cases where neighbours are killing neighbours is more troubling and, in a way, it gets closer to the human condition.

suspect a similar rupture occurred in the 1970s within the chimpanzee group at Gombe, Tanzania, observed by Jane Goodall.

However, limited understanding of chimpanzee behavior at the time prevented full recognition of the in-group violence. The Ngogo case provides clearer evidence due to long-term monitoring. Evolutionary anthropologist Brian Wood, who studied the Ngogo chimpanzees but was not involved in the research, explained the attacks in terms of Darwinian fitness.

The western group increased its reproductive success by reducing that of the central group. Anthropologist Sylvain Lemoine described the event as the first thoroughly reported case of civil warfare in chimpanzees, highlighting the role of social ties in group cohesion. The study indicates that chimpanzee civil wars occur approximately every 500 years, based on genetic evidence.

Human activities such as deforestation, climate change, and disease outbreaks could increase the frequency of such conflicts by disrupting social cohesion. Chimpanzees are classified as threatened with extinction, raising concerns for conservation efforts.