The Bili Ape of the Congo

by Brian Dunning
August 20, 2019

In the darkest jungles of the Congo is said to lurk a recently discovered great ape: large, upright, aggressive, and distinct from both chimpanzees and gorillas. It is called the Bili ape, known from both eyewitness accounts and even directly evidenced with unusual skulls that cannot otherwise be classified. Cryptozoologists point to the Bili ape as proof that mysterious new species are out there for real, just waiting to be discovered. Today we're going to go there ourselves, and see if we can sort out what part of the Bili ape is legend, and what part of it has been confirmed by science.

The Bili Forest lies in the northern part of the DRC (Democratic Republic of the Congo) in a land almost entirely undeveloped and dense with jungle. About half the world's chimpanzees live in the DRC, so naturalists have always known — or at least assumed — that chimps would be found here as well. The range of the Bili ape is not formally established. Sometimes it's called the Bongo Ape (Bili and Bongo are two towns in the region), but scientists today refer to the 55,000 square kilometers where this population is found as the Bili-Uéré region, named for Bili and the Uéré river, a tributary of the larger Uélé river. Half the region is north of the Uélé and consists of scattered jungle and savannah; the other half is south of the river and is solid dense jungle. In the mid-1990s, a Swiss author, bushmeat activist, and photographer named Karl Ammann saw mysterious skulls in a Belgian museum that appeared to be neither gorilla nor chimp, and that were said to have been collected from the Bili-Uéré region by early colonists in 1898. Determined to find these creatures, Ammann went there in 1996 and right away began to find evidence of a new type of mystery ape, one that looked most like a chimpanzee but was larger and grayer, and had habits that were like those of gorillas. It slept on the ground, in defiance of the predators that drive ordinary chimps up into the trees, and did other things that were characteristic of gorillas, not of chimps. Most impressively, he brought back a skull that appeared to be chimpanzee, but was larger and had a gorilla's sagittal crest. Ammann also brought back legends from Congo locals, stories of aggressive mystery apes six feet tall, who walked erect and were immune to poison darts. In the local language, Zande, there were many names for these apes. Amman translated two of them to mean The ones which beat the tree! and The one which kills the lion.

For several years, civil war in the DRC made it impossible to mount a scientific expedition to follow up on Ammann's observations and evidence. But by the early 2000s, Ammann was able to return with a growing number of scientists. Among them was Dr. Shelly Williams, armed with a $20,000 research grant from National Geographic, who made sensational reports to the American press. 2003 saw a flood of articles promoting the mystery of giant apes in the Congo in publications like CNN, the Associated Press, and National Geographic, often citing Shelly Williams as the first scientist to document the creature. In 2005, Time magazine wrote that what she called the "mystery ape":

... had a much flatter face [than chimpanzees] and [a] straight-across brow like gorillas and turned gray early in life. Females lacked chimps' genital swelling. Two or three would nest on the ground, with others low in nearby branches. They made a distinct vocalization like a howl and were louder when the full moon rose and set. "The unique characteristics they exhibit just don't fit into the other groups of great apes," says Williams. The apes, she argues, could be a new species unknown to science, a new subspecies of chimpanzee or a hybrid of the gorilla and the chimp.

And that was where the legend of the Bili ape essentially stopped. Combined with numerous photographs of chimps with sensational captions, various skulls, video footage shot by Dr. Williams, and plaster casts of footprints, this is the extent of the pop-culture portrayal of the Bili ape. Quotes from Dr. Williams are the original source of the claims that the animal is a hybrid or otherwise different from any established species, or that it is of great size. And, as we see so often on Skeptoid, the urban legend goes just far enough to encounter problems.

The first indication that some skepticism was warranted was when it turned out Dr. Shelly Williams had no relevant credentials; her Ph.D was in experimental psychology. Moreover, it turned out that her claims of a possible hybrid were not representative of what the other scientists on site had already determined. In a 2003 letter blasting her popularly reported claims, Ammann wrote:

There are at least two pictures available of chimpanzees looking larger than what is considered average size, but the aforementioned scientists do not consider them conclusive. They are, however, a lot more conclusive than any of the video footage Dr. Williams returned with (much shot by one of the trackers, who has been with the project since 1999). Besides that footage, there is absolutely nothing Dr. Williams has contributed that was not known and established before she got involved.

Needless to say, that we are totally dismayed with Dr. William's unprofessional attitude and her unscientific and mendacious press release.

Tragically, Dr. Williams was injured and paralyzed in 2005 and was never able to continue her part in the Bili ape story. With the end of her participation came the end of the sensational press releases about giant mystery apes in the Congo. The scientists were still there studying the Bili-Uéré, and have been ever since; but the fact that we no longer get reports of giant mystery apes should tip us off that maybe that's not what the actual science says.

This actual science comes from the actual scientists — anthropologists, biologists, and primatologists — who were also there with Amman in the early 2000s, but who spent their time actually studying the apes, and not writing press releases for National Geographic. One, Thurston Cleve Hicks, presented the results of DNA analysis at the International Primatological Society in Uganda. Confirmed by three different labs, the Bili apes are — drum roll please — ordinary members of the common Eastern chimpanzee subspecies, Pan troglodytes schweinfurthii, the same as all the other chimps in the region. They are, beyond any doubt, not mutants or hybrids. They are common chimpanzees. When New Scientist magazine reported these results, Hicks found he had a plate full of "gorilla hybrid" misinformation from Williams' press releases that he already had to debunk. "I see nothing gorilla about them," he told New Scientist. "The females definitely have a chimp's sex swellings, they pant-hoot and tree-drum, and so on." Even after the article came out, Hicks saw that its authors had further embellished their description of the Bili-Uéré with more of Williams' sensationalism, and wrote the following in a letter to the editor a few months later:

Two points in your article about our work on Bili's "giant apes" require correction (1 July, p 14). It is an exaggeration to say that the chimps' skulls have a sagittal crest. Only one skull has been found with a small sagittal crest. You also state that recordings exist of the Bili apes howling at the moon. If these recordings exist, we would very much like to hear them. It must be stated very clearly: the Bili apes do not howl at the moon.

One of the main goals of this study has been to puncture the myths surrounding the Bili apes and paint a more realistic portrait of the genetics, behaviour and ecology of these chimpanzees, which, it is now clear, are not a hybrid or a new species.

About the only physical trait of the Bili-Uéré chimps that does seem to be unusual is that their heads may be somewhat larger than the average chimp, and some reports remain that their overall size may be a bit larger as well, and that they may gray earlier and more. How could we account for this, if they're not at least a distinct subspecies?

Recall your high school biology. You inherited one gene for eye color from your mother and one from your father. If you happened to get both recessive genes for blue eyes, you'll have blue eyes; otherwise, you'll have brown eyes. These alternative forms of the same gene are called alleles, and when you travel around the world you'll find populations where certain alleles are found in greater frequencies. Varying allele frequencies associated with traits like skin color, hair type, and face shape in places like Nigeria, China, and Norway are what gave rise to the idea of race; but as we now know, we're all exactly the same race — the human race — with different allele frequencies that can be endlessly mixed and matched. The chimpanzees in the Bili-Uéré region are one such population. Compare Bili-Uéré chimps with populations in other parts of the DRC and you may indeed find greater frequencies of alleles favoring large size and early graying of fur, to whatever extent these traits may actually exist in the Bili-Uéré population. Even the sagittal crest on the skull that Amman found is rare for chimps, but still within the range of normal variation.

Hicks went on to become the lead author in what is today the most authoritative paper published on the Bili-Uéré chimps. It's a 2019 article published in Folia Primatologica, the official journal of the European Federation for Primatology. It's called "Bili-Uéré: A Chimpanzee Behavioural Realm in Northern Democratic Republic of Congo" and documents the results of twelve years of field study between 2004 and 2016. Crucially, not once in the entire 62-page paper do any of the thirteen authors ever mention the Bili-Uéré chimps' size or anything unusual about their appearance; the paper talks only of their use of tools and other behaviors, and how it differs from other chimp populations. In short, the Bili-Uéré use different sizes and types of sticks to retrieve honey and ants and do the various other tasks chimps perform with tools. Thus the paper refers to the Bili-Uéré as a behavior realm, and not as a distinct subspecies. To the scientists who study the Bili-Uéré, the genetic differences in them from other chimps is so unremarkable that it is not even mentioned in current scientific literature.

And so we conclude the story of the Bili ape as we conclude so many exaggerated urban legends here on Skeptoid. Something happened — in this case, a particular population of chimps was studied — and then large parts of the story were greatly exaggerated and sensationalized by one imaginative author — in this case, Shelly Williams, working for National Geographic, a publication which (at that time) was just beginning its transformation from a respected science magazine into one that mixes in just enough mass-media sensationalism to keep the readers hungry for more. Pop culture snapped up and embraced that exaggerated story, and the inevitable result is found in today's YouTube videos and articles on cryptozoology websites promoting the Bili ape as some kind of mutant simian monster.

By Brian Dunning
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