Chimp Civil War Observed by Jane Goodall Began With Tensions Between Three Males
The only civil war ever observed in wild chimpanzees was fueled by power, ambition, and jealousy, new research finds.
Leakey was a male elder in Tanzania. When he died in October 1970, a large male named Humphrey rose from the beta to the alpha position and was poised to assume a leadership position. The anticipated simple transition was not to be
Two brothers who lived to the south of Humphrey, Charlie and Hugh, ganged up on the alpha male and intimidated him. Humphrey, in turn, threw rocks during charging displays. Other males watched the aggressive moves.
Then the real battle began. Humphrey and other males moved into the rebel territory and savagely beat victims, often taking over their land. The bloodshed went on for four years, during which seven rebel males died or vanished. At the end of the battle, the southern community, by then known as Kahama, was extirpated.
Humans can engage in similar, brutal behavior, but the players in this case were chimpanzees at Gombe National Park, which were studied by renowned primatologist Jane Goodall.
The "Four-Year War" from 1974–1978, as Goodall later described it, represents the only civil war ever observed in wild chimpanzees. Her newly digitized field notes enabled researchers to take a closer look at the seeds of the conflict, which are reported in the American Journal of Physical Anthropology.
The authors conclude that the power struggle between Humphrey, Charlie, and Hugh, along with an increasing ratio of males to reproductively available females, likely caused the once united community to split — known as a fission — and erupt into violence.
"Although the scale of the violence after the fission may be unusual, inter-community violence and killings are a ubiquitous feature of chimpanzee social behavior, so the post-fission violence is not unique," lead author Joseph Feldblum of Duke University's department of evolutionary anthropology told Seeker.
"What was unprecedented," he added, "was the division of the community, and given the extirpation of the Kahama community, it makes sense that permanent fissions are pretty rare in chimpanzees."
Senior author Anne Pusey, also from Duke, has spent the last 25 years archiving and digitizing Goodall's copious hand-written notes and check-sheets. Pusey was a doctoral student at Gombe from 1970-1975 and witnessed many of the key events firsthand.
"I remember an occasion in 1972 when I was following a group of mostly northern chimps towards the south," Pusey told Seeker. "There was a big group ahead, pant-hooting loudly, and Humphrey and another mature male touched hands and headed back north, while the others, including young northern males, went on and eventually joined the group that included most of the southern males, with much excitement and calling."
Later, at the beginning of 1975, when the two groups had completely separated and some of the southern males had already been killed, Pusey was with some northern chimps as they traveled south, rested silently on the top of the ridge at the edge of their territory and suddenly spotted Sniff — an adult male — and some of the other Kahama chimps in the trees in the valley below.
"Sniff and the others climbed down and disappeared," she said, "and the chimps I was with started stalking them, moving very stealthily and sniffing the vegetation as they went, but they didn’t find them and eventually turned back to their territory, and pant-hooted loudly after they had got back over the ridge."
Curious about the shifting alliances among these and the other male chimps, 19 in total, Pusey and her colleagues mapped the chimps' social networks at different periods between 1967 and 1972 to pinpoint when relations began to fray.
The analysis went back into the 60s in part because, beginning in 1963, initial observations of the original study chimpanzee community were made at a "feeding station," where other researchers used bananas to habituate the chimps and to facilitate observations.
By 1966, these researchers recognized that, of the 19 mature and adolescent males, some spent more time to the north of the feeding station and others spent more time to the south. These are the once loosely defined subgroups that later became known as Kahama to the south and Kasekela to the north.
In more recent years, some scientists have suggested that the friction between the groups was sparked by the feeding station. As Ian Morris writes in his book War! What Is It Good For? (Farrar, Straus and Giroux, 2014): "Goodall, they insisted, had caused the war. In her efforts to get the chimpanzees comfortable around humans, she had fed them bananas, and competition over this rich food, the critics suggested, had corrupted the chimps' naturally peaceful society and turned it violent."
Researchers ended provisioning in Gombe in 2000.
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While Feldblum, Pusey, and co-authors Sofia Manfedi and Ian Gilby cannot rule out the possibility that provisioning had some effect on the chimps' community cohesion, the new network analysis paints a different picture of the causes than do Goodall's critics.
For the new analysis, Feldblum and his team charted all of the 19 males and considered that, if two were spotted arriving together at a feeding station together more often than other pairs, they had a social bond.
As for what leads to such bonds, relatedness and social status appear to be factors.
"Maternal brothers seem to cooperate and associate with each other more than unrelated individuals, and males in our population tend to be more gregarious in general than females," Feldblum said. "There's some evidence also that males of similar ranks might be more likely to form social bonds."
Next, the researchers identified the most tightly knit groups in each network and determined how much their members changed over time. The authors show that, from 1967-1970, males in the original group intermingled.
Following Leakey's death, the clusters of males grew more distinct, with some spending more time in the north, and others in the south. By 1971, the northern and southern males met less and less often. When they did encounter each other, as Pusey later witnessed, they would hurl branches, hoot and charge through the forest as a show of strength.
Within a year, the cliques began to harden and became increasingly exclusive, the network analysis reveals. Where once the chimps groomed and spent time with other males both inside and outside their subgroup, by 1972 they socialized almost exclusively with males on the inside, with minimal range overlap between northern and southern males.
The two territories were similar to each other, in terms of their landscape.
The national park as a whole consists of "a very mosaic habitat," Feldblum explained, "and the good areas are those in valleys through which streams run, and luckily there are lots of such valleys in Gombe."
The researchers are unclear what led to the increasing ratio of males to reproductively available females throughout the northern and southern chimp communities.
"In a social group of the size observed in Gombe, random fluctuations could certainly account for significant changes in sex ratio," Feldblum said, adding that another possibility "is that there were other females that weren't habituated yet."
Female chimps can be the victims of male violence. In some areas of Uganda, for example, researchers have observed male chimps routinely beating the females with whom they mate. The beatings, it is theorized, could deter the females from mating with others.
Female chimps may also be the aggressors. Goodall and her team, for example, observed a mother and daughter grab, kill and consume infant chimps from their own community. Similar brutality has also been observed in Uganda.
Humans, of course, are capable of all of these violent behaviors: rape, sexual abuse, warfare, killings, kidnappings, and land grabs.
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A possible driver of such actions in both chimps and humans is what author Gregory Johnson, in the book Theory and Explanation in Archaeology (Academic Press, 1982) termed "scalar stress." This refers to difficulties maintaining or keeping track of relationships, particularly within groups of increasing size.
"There's evidence from several species of primates and other mammals that there's an optimal group size, which is reflected in reproductive patterns, stress hormones, and space use," Feldblum said. "Things may be more complicated in chimpanzees and humans, though."
He explained that chimpanzees live in a "fission-fusion" society, where animals temporarily split from the larger group to do things like forage, but then go back to the larger group, often to sleep in one place.
Feldblum said that because of this type of society, "all members of the community are rarely together, so group size probably limits chimpanzee group formation differently than it does in some other primate species. Further, because of their intense territoriality, selection probably leads to larger group sizes in chimpanzees."
He continued, "Humans are more complicated still because of their multi-level social organization, and researchers who study pre-industrial human populations tell me that even getting a handle on what constitutes a group for the calculation of group sizes can be tricky."
Chimpanzees and humans are closely related, so determining their optimal group sizes, factors underlying social bonds, and reasons for cohesion breakdown could provide clues about the forces that bind social groups together in the first place.
Feldblum is expanding on the recent work with a follow-up project investigating the predictors of community structure in two communities of east African chimpanzees: one in Gombe and the other in Uganda.
He said, "I plan to extend these efforts by using the network structure of groups to investigate the costs and benefits of group living, with a view to making broader comparisons among non-human primate and human groups."