John Mitani, a primatologist who co-founded the Ngogo Chimpanzee Project in Uganda's Kibale national park, has described witnessing what may be the first recorded “civil war” among wild chimpanzees – a conflict that killed nine males and 19 infants.
Mitani first arrived in Kibale in the summer of 1995, coming from work with chimpanzees in the Mahale mountains of Tanzania. At the time, Mahale was home to the largest known chimp population, with about 100 individuals. But rumours suggested that this section of Kibale – only reachable via a 12-hour drive from the capital, Kampala – might host an even more unusual abundance of apes.
“It only took a few days to realise that something weird was going on at this place,” Mitani, now 72, recalls. “There were chimps everywhere.”
Building trust with the Ngogo chimpanzees
With his colleagues, Mitani counted nearly 200 chimpanzees living peacefully together in the forests of Ngogo, a research area in the central section of Kibale first established in the 1970s for the study of red colobus monkeys. Such a large chimp troop was then unheard of in primatology.
Later that year, Mitani co-founded the Ngogo Chimpanzee Project with Yale university primatologist David Watts, using a $500,000 (£380,000) award from the US National Science Foundation. Three decades on, the project is one of just 12 long-term studies worldwide of chimpanzees in their natural environment.
It took years to build trust with the population. The chimps were not accustomed to human presence and would run away whenever researchers approached. The first ape to break the ice was a 25-year-old male with an easily identifiable cleft palate that Mitani later named Hare.
Stunning discoveries and a violent split
Mitani estimates he has spent 85 months of his life hiking the forests of Ngogo, or approximately seven years. The findings from Ngogo have stunned the scientific world. Mitani and his colleagues documented the lowest mortality ever recorded for a wild chimp population, and found that unrelated males could form strong alliances and cooperate.
But the most notable – and disturbing – finding began on a June day in 2015. Mitani and his fellow researchers were observing a cluster of the group when the chimps began to display nervous behaviour and scattered at the sounds of approaching group members. “All of a sudden, the individuals I was following just ran down the hill for no apparent reason,” Mitani says. “Chaos erupted. They started to run around and chase each other.”
That moment was the first sign of what would become a years-long bloody conflict, chronicled in the 2023 Netflix series Chimp Empire, between a once close-knit group of chimps. In a study published this April in the journal Science, Mitani and his colleagues describe what may be the first “civil war” among wild chimps.
Personal toll and a warning about funding
By 2018, two distinct chimp groups had formed in Ngogo. Nine males and 19 infants have been killed during the conflict. Scientists later found that the unexpected result of this lethal aggression was that female fertility doubled and offspring survival increased substantially at Ngogo.
For Mitani, witnessing the split was far more personal. “I was in denial. I was still in this mindset that they were doing so well together as a big group,” he recalls. “It’s been hard to watch. In the first 20 years, going back to see the chimps was fun. I always looked forward to these visits. But it’s gotten to be increasingly difficult to go back and see this, to see these killings continue.”
It took him more than a decade to write the paper on the dark events. “I think I was dragging my heels because maybe I didn’t really want to write about this.”
Mitani pushes back against the takeaway that the civil war says anything about humans’ evolutionary propensity for violence. This behaviour has not been witnessed among bonobos, with whom we also share a common ancestor dating back approximately 8m years. “Many of us who study chimps emphasise the similarities, and for good reason,” Mitani says. “But when it comes to the behavioural similarities, sometimes I think my colleagues stretch things a bit too much. If there is one thing I’ve learned from studying chimps all these years, it is that they are not us.”
Though the greatest threat the Ngogo chimps now face is, in a way, themselves, Mitani says the presence of researchers over many decades has helped to conserve these populations. Researchers work with the wildlife authority to remove snares for other wild game that occasionally trap a chimp by mistake.
Mitani worries for the future of research at Ngogo. The project has received the bulk of its funding from the US National Science Foundation’s behavioural and cognitive sciences division. Under the Trump administration’s proposed 2027 budget, that funding is due to be eliminated.
“The chimps there have many more important stories to tell us,” Mitani says. “This is one of the reasons I am so concerned about the war on science and truth in this country.”
He will return again to Ngogo this month – and for as long as he is able. “The funny thing is that the hills at Ngogo get increasingly steeper every year. And the distance between the trails seems to get longer. But I feel blessed that I still can do it.”
If there is any legacy to his life’s work, he hopes that being able to impart some knowledge of the complex lives of these animals will give people a better appreciation of the chimpanzees. “That would be the grand, big hope.”
