Published: April 2008 Fongoli Chimps
Almost Human
On the savannas of Senegal, chimpanzees are hunting bush babies with spearlike sticks. This hothouse of chimp "technology" offers clues to our own evolution.
By Mary Roach

Daybreak is sudden and swift, as though an unseen hand had simply reached out and raised a dimmer switch. Cued by the dawn, thirty-four chimpanzees awaken. They are still in the nests they built the previous night, in trees at the edge of an open plateau.

A wild chimpanzee does not get out of bed quietly. Chimps wake up hollering. There are technical names for what I'm hearing—pant-hoots, pant-barks, screams, hoos—but to a newcomer's ear, it's just a crazy, exuberant, escalating racket. You can't listen without grinning.

These are not chimps you've seen in these pages before. They're savanna-woodland chimps, found in eastern Senegal and across the border in western Mali. Unlike their better-known rain forest kin, savanna-woodland chimps spend most of their day on the ground. There is no canopy here. The trees are low and grow sparsely. It's an environment very much like the open, scratchy terrain where early humans evolved. For this reason, chimpanzee communities like the Fongoli group—named for a stream that runs through its range—are uniquely valuable to scientists who study the origins of our species.

By 8 a.m. my chintzy key-chain thermometer says it's 90 degrees. Our shirts are marked by the same white salt lines that appear on people's boots in winter. Here it's salt from sweat. The plateau we're crossing is a terrain of nothing, of red rocks and skin cancer, with no trees to break the fall of equatorial sun. In our backpacks we each carry three liters of water. It was cool when we set out. By noon it will be hot enough to steep tea.

I'm not complaining. I'm making a point. Life on the savanna—even so-called mosaic savanna, tempered by patches of lusher gallery forest along the streambeds—is exceptionally harsh. If you are a primate used to greener terrain, you must adjust your behavior to survive. Our earliest hominin (meaning bipedal ape) ancestors evolved more than five million years ago during the Miocene, an epoch of extreme drying that saw the creation of vast tracts of grassland. Tropical primates on the perimeter of their range no longer had plentiful fruits and year-round streams and lakes. They were forced to adapt, to range farther in their search for food and water, to take advantage of other resources. In short, to get creative.

In 2007 Jill Pruetz, an anthropologist at Iowa State University, reported that a Fongoli female chimp named Tumbo was seen two years earlier, less than a mile from where we are right now, sharpening a branch with her teeth and wielding it like a spear. She used it to stab at a bush baby—a pocket-size, tree-dwelling nocturnal primate that springs from branch to branch like a grasshopper. Until that report, the regular making of tools for hunting and killing mammals had been considered uniquely human behavior. Over a span of 17 days at the start of the 2006 rainy season, Pruetz saw the chimps hunt bush babies 13 times. There were 18 sightings in 2007. It would appear the chimps are getting creative.

There are individuals who are uncomfortable with Pruetz's tales of spear-wielding chimps, and not all of them are bush babies. Harvard professor of biological anthropology Richard Wrangham, who has studied chimpanzee aggression in Uganda's Kibale National Park, has been skeptical. Wrangham is widely known for his "demonic male" theory, which holds that the savage murders carried out by male chimps while policing their turf are suggestive of a violent nature at the core of man. Primatologist Craig Stanford, author of The Hunting Apes, also downplays the importance of Pruetz's findings. "This behavior is fascinating, but the observations are so preliminary that it merits only a short note in a journal."

The report ran in the major journal Current Biology, and people seemed to find it interesting. In the week that followed, Pruetz's findings were featured in more than 300 news and science outlets, including New Scientist, the New York Times, the Washington Post, and NPR's Science Friday. The Smithsonian Institution requested one of the spears. In short, it was the most widely talked about primatology news since the reports of infanticide and cannibalism at Jane Goodall's site at Gombe in the 1970s.

Pruetz and I watch the chimps climb from their nests. A large male hangs from a low branch by one arm, swinging gently, in no hurry. The silhouette is utterly erect, arrestingly humanoid. He lets go, drops to the ground, and moves off across the plateau. The symbolism is impossible to miss. Here is a chimpanzee, thought by many to be the closest thing we have to a living model of our early hominin ancestors, literally dropping from the trees and moving out into the open expanses of the savanna. It is as though we are watching time-lapse footage of human evolution, the dawn of man unfolding in our binoculars.

Chimps that live on the ground, rather than in the safety of treetops, tend to be wary of large strangers. Jill Pruetz spent four years getting the Fongoli chimpanzees accustomed to the presence of humans—what primatologists call habituating them—and the past three summers observing them. Six days a week, from dawn to dusk, she follows the chimps.

It is not glamorous work. It's hot and filthy and exhausting. Home is a mud-walled hut and a drop toilet shared with 30 Fongoli villagers. Dinner is peanut sauce over rice, except when it's peanut sauce over millet. If the chimps wander unusually far, Pruetz gets back to the village so late that her portion has long ago been fed to the dogs. Sometimes, rather than hike the five miles back to camp, she curls up and sleeps on the ground (or takes a nap in an abandoned chimp nest). She has gotten malaria seven times.

Yet you rarely meet people who love what they do as much as Pruetz does. Right now she is sitting on the ground, jotting notes with one hand and slapping sweat bees with the other. Blood from a blister has soaked through the heel of her sock. To listen to Pruetz, we might as well be in Paris. "Sometimes," she says, scratching a bite, "I think I'm going to wake up and it's all a dream." The payoffs have been dramatic. In addition to using tools to hunt, Fongoli chimps have been exhibiting some other novel behaviors: soaking in a water hole, passing the afternoon in caves.

At 24 square miles, Fongoli is the largest home range of any habituated chimpanzee group ever studied. (Jane Goodall's Gombe chimps, by comparison, roam over five square miles.) Craig Stanford likens foraging over a large range to knowing one's way around an enormous supermarket. Like Pruetz, he believes the chimpanzees are not foraging at random, but moving with foresight and intent. "You don't stroll down the aisles hoping to catch a glimpse of the broccoli. You know where each item is, and in which months seasonal foods are likely to be in stock." The same, he thinks, holds true for chimpanzees.

"Ecological intelligence" is the name of the theory that some primates, including those of our lineage, have evolved larger, more complex brains because it helped them adapt to the challenges of surviving in a less giving habitat. "The first push toward a larger brain," writes Stanford, "may have been the result of a patchily distributed, high-quality diet and the cognitive mapping capabilities that accompanied it."

High-quality, meaning: meat. The shift toward eating more meat may have played an important role in the evolution of a larger, more sophisticated brain. Here's how the thinking goes. Brains are, to use terminology coined by researchers Leslie Aiello and Peter Wheeler, "expensive tissue." To keep a bigger brain functioning, some other organ or system needed to become more streamlined. A chimp doesn't have to eat nearly as much of an energy-rich food like meat as he would of low-nutrient plant matter. Expending less energy on digestion means you can afford to apply it elsewhere, perhaps to power an expanded brain.

As if on cue, a female named Tia appears in our sight lines 20 feet ahead, sitting on a boulder pulling raw flesh off a limb like a picnicker with a comically huge drumstick. Pruetz raises her binoculars, then lowers them again. "Holy crap! It's a bushbuck." She can tell from the white markings on the hide, a long strip of which hangs from the leg. "That's the biggest animal I've seen them eat." She surmises it was a fawn. Gombe chimps have occasionally killed bushbuck fawns as well. They are the largest prey on record for a chimpanzee.

Hunting at Fongoli coincides with the rainy season, and Pruetz has some theories about why this is. As water holes fill and shoots and other greenery become more plentiful with the rain, the land provides enough sustenance to support a sizable group of chimps on the move. There are advantages to traveling in a large group. A single chimp or small group that heads out on its own can easily lose track of the community for days at a time. For a chimp, sociability is important. Pruetz points to an estrous female named Sissy, her pink swelling bobbing behind her like a bustle. "Otherwise you miss out on that." She means, of course, the chance to mate, to pass along your genetic material.

Right now, two rains into the rainy season, there's enough water and food for the group to travel together, but just barely. Pruetz believes it is this scenario—large crowd competing for limited resources—that has pushed certain members of the community to try their hand at novel things.

Things like sharpening sticks to spear bush babies. It is a different kind of hunting than the organized colobus monkey raids documented at other sites. A chimp who comes across a dead, hollow tree limb—promising real estate for day-sleeping bush babies—will sometimes break off a branch from a nearby tree, remove the leaves and the flimsy ends, and then use its teeth to whittle one end to a point. This tool is then stabbed into an opening in the tree limb until the animal inside is out of commission. Whereupon it is eaten, head first, Pruetz says, "like a Popsicle."

Adult female and juvenile chimps—the low rankers—have been seen hunting bush babies most often. This makes sense. Dominant males are not generous with food they find, and no one can force them to share. Fongoli females appear to have taken matters into their own hands.

Now here comes Farafa, her baby Fanta on her back and a bushbuck haunch in her jaws. It's a complicated, messy piece of anatomy, with sinew and hide hanging off one end. Tia sees her and stands up to move away. My last glimpse of Tia is with her now bare bone brandished above her head, standing erect, as though reenacting the "dawn of man" scene from 2001: A Space Odyssey.

Fongoli chimps have a flair for the dramatic.

The media ruckus spurred by Pruetz's report of spear-wielding chimps made her absence as a speaker at last year's Mind of the Chimpanzee conference perplexing. She was in the audience but wasn't invited to present a paper. On top of that, Pruetz's post-doc adviser, Cambridge University primatologist William McGrew, made a passing reference to the Fongoli hunting behaviors but did not credit her with the work. He credited her co-author and former student Paco Bertolani, now a student of McGrew's. Bertolani witnessed the first—of now 40—observed instances of the behavior, but scientific etiquette would call for the principal investigator to be mentioned. McGrew apologized afterward. Some primatologists took Pruetz to task for overstating the bush-baby-spearing behavior. When your prey is smaller than your hand, are you really hunting? Male primatologists tend to make the distinction along gender lines: The traditional view has been that chimpanzee hunting—along with aggression and murder—is the domain of the male. "Small mammals that females and juveniles obtain are 'gathered,' " Pruetz says, "while males 'hunt.' " Females, the thinking goes, don't hunt because they don't need to; male chimps are thought by some to trade meat for sex, but Pruetz hasn't seen this at Fongoli.

I'm going to weigh in, for what it's worth. One day while accompanying Pruetz, I watched a young chimp named David at a bush baby tree hole. We heard him well before we saw him: a resounding THONK that caused Pruetz to stop in her tracks and go, "Hold on, hold the phone, that sounds like a spear!" We looked around, and there he was, standing on a branch in a kino tree, holding on with one hand and waving a thick, three-foot-long stick over his head. He slammed it down into the hole, then examined the tip. Concluding that no one was home, he took off, leaving the spear protruding from the hole. The violence and foresight with which he undertook his task did not suggest an animal quietly foraging. His aim was unmistakable: to kill, or at least incapacitate, whatever was in there.

Many of Pruetz's reviewers tripped over the word spear. For one thing, it suggests a projectile and a more Cro-Magnon-esque technique: something aimed and thrown. (Pruetz says she had spearfishing in mind when she chose the noun.) Stanford suggested bludgeon. But bludgeons are blunt, not sharpened. Another offered dagger. Someone else wanted bayonet. In the end, Pruetz took spear out of the title and worded her text more cautiously, making reference to a tool "used in the manner of a spear." (The press picked up on it anyway. "Spear-Wielding Chimps Snack on Skewered Bushbabies" ran the giddy NewScientist.com headline.)

I asked Pruetz if perhaps she's been the victim of an alpha male primatologist conspiracy. She laughed it off. "Yeah, maybe I'm not pant-grunting enough." (The pant-grunt is an expression of submissiveness; a chimp that encounters a higher ranked peer and fails to pant-grunt is asking for trouble.) It's also possible that humans are simply resistant to the notion that anyone other than a human makes weapons for killing.

You would think that primatologists, more than other scientists, would be comfortable with the shifting boundaries between chimpanzee and human. Their gene sequences are around 95 to 98 percent the same. (This is less meaningful than it sounds. Humans share more than 80 percent of their gene sequence with mice, and maybe 40 percent with lettuce.) A recent exploration of the human and chimpanzee genomes, undertaken by David Reich and colleagues at the Broad Institute of MIT and Harvard in Cambridge, Massachusetts, suggests that chimpanzees and early hominins may have interbred after the two lines initially split. Yet there seems to be a lingering discomfort with findings that, as Pruetz puts it, "chip away at our superiority."

Since the earliest days of primatology, discoveries of chimp behavior that threaten to undermine the specialness—the apartness—of human beings have met with rancorous resistance. Many anthropologists bristled at the first references to chimpanzee "culture"—a concept widely accepted today. Jane Goodall's first reports of chimps making tools (for termite fishing) were as contentious in their day as more recent claims of teaching chimps to use language. At the Great Ape Trust, in Des Moines, Iowa, a bonobo named Kanzi has learned to communicate through symbols. Kanzi commands about 380 symbols and shows signs of understanding their meaning. When he was frightened by a beaver, an animal for which he had no symbol, he selected the symbols for "water" and "gorilla" (an animal that scares him). Critics say the communications are purely conditioned behavior. Novel uses of symbols—e.g., "water gorilla"—are dismissed as coincidence.

An exception to these attitudes has long been found at the Primate Research Institute at Kyoto University. Japanese primatology is consistent with the Buddhist precept that humans are a part of the natural world, not above or separate from it. At the Mind of the Chimpanzee conference in Chicago last year, Tetsuro Matsuzawa spoke of primatology's early years, when scientists "didn't know how much close we are." He added, with unabashed awe: "So close, like horse and zebra." In the background of one Japanese researcher's slides was what looked to be a chimp wearing glasses. I turned to the man next to me. "I'm sorry," I said. "I must be losing my mind. Was that chimp wearing glasses?" The man told me the Japanese primatologists had noticed the chimp was nearsighted and had him outfitted with prescription lenses. (I later learned he was wrong: This chimp was just playing with the glasses. There once was a research chimp whose caretakers ordered her glasses, but that was in the U.S., not Japan.)

No one around Fongoli is sending chimps to the optician, but the animals are accorded a remarkable amount of respect by locals. Kerri Clavette, Pruetz's intern, interviewed villagers about their beliefs regarding chimpanzees and whether they hunted them. Among the region's main tribes—the Malinke, Bedik, Bassari, and Jahanka—chimps, compared with monkeys, have an elevated, almost human status. "Chimpanzees came from man, as they have similar hearts," a villager told Clavette. Behaviors normally associated with a baser nature—such as walking on all fours—were given a respectful spin: "Chimpanzees walk on their knuckles to keep their hands clean to eat with." Chimpanzee origin myths feature humans running off into the woods for some reason—war, fear of circumcision, fear of being punished for fishing on Saturday—and staying there so long that they turn into chimpanzees.

Despite a local history of killing chimpanzees for medicinal reasons—the meat laid on a person's arm or eaten for strength, the brains prepared with couscous to treat mental illness—villagers rarely hunt chimpanzees in eastern Senegal today. Sadly, the taboo against eating one's almost kin has broken down in central Africa, where turmoil has worsened dire economic circumstances and chimps are sold as bush meat.

Attitudes in the West have been shifting gradually over the past few decades. The sequencing of the chimp genome, completed in 2005, has focused attention anew. New Zealand, the Netherlands, Sweden, and the United Kingdom have all passed legislation limiting experimentation on great apes, and the Balearic Islands in Spain passed a resolution in 2007 granting them basic legal rights. In 2006 an Austrian animal rights organization submitted an application to a district court in Mödling to appoint a legal guardian for a chimp named Hiasl. The strategy was to establish "legal person" status for the hairy defendant. (The judge was sympathetic but refused.) It is perhaps less problematic to view the situation as does The Third Chimpanzee author Jared Diamond: not that chimps are a kind of human, but that humans are a kind of chimp.

The chimp named Sissy sits motionless and hunched at a low termite mound twenty feet from us.

Only her right arm moves, pushing a saba vine probe into a hole and gently withdrawing it, with termites clinging to it. She raises it carefully to her mouth like a pensioner spooning soup. The mound is across an open lay of pebbly, brick-colored laterite that gives the ground the look of a clay tennis court.

Like fly-fishing, termite fishing is a meditative, deceptively nuanced activity. I tried it a few times and could not even find an active hole. My probe never sinks farther than an inch or so; the chimps regularly bury theirs a foot or more. They can find active holes by smell, inserting a probe and then sniffing the end of it for the smell of soldier termite pheromone.

Fongoli chimps eat termites year-round, not just in the dry season, when other foods are scarce. Termites make up, at bare minimum, 6 percent of the Fongoli chimps' diet. We know this because most evenings at six o'clock research assistant Sally Macdonald sits down with a set of sieves and buckets, and one or two ziplock bags of the chimp feces that the researchers bring back most days. She scans the fruit seeds, estimates the percentage of fiber from leaves and shoots, and takes note of bones and termite pincers. "Science in all its glamour," deadpans Macdonald, whose mother sends ziplock bags but does not know their fate.

A quick glimpse into the bucket reveals that saba fruit is the chimps' mainstay this time of year, an adult averaging 30 to 40 a day. The Fongoli record for saba seeds in a single fecal sample—499, compared with an average of 75—probably belongs to a male named Mamadou. Which may explain why Mamadou is, quoting Pruetz, "especially gassy."

Pruetz's Ph.D. student Stephanie Bogart says part of the reason chimps fish termites is that they're an exceptionally calorific food. A 3.5-ounce serving of termites has 613 calories, compared with chicken's 166. But 3.5 ounces of soldier termites is hundreds of insects, fished piecemeal from a mound. It's like eating cake one crumb at a time. The chimps must really like them.

Sissy gets up from her spot at the termite mound to select a new tool. She breaks off a length of vine, inspects it. Satisfied, she sticks it in her mouth and carries it back to the mound like a seamstress holding pins between her lips. Pruetz and others argue that female chimps are not only more skilled than males at crafting and using tools, but also more diligent. Craig Stanford agrees that it might well have been our female ancestors who first steered the culture toward tool use. Early tools for foraging, he imagines, gave way to tools for scavenging meat from carcasses killed and abandoned by large carnivores. These tools in turn may have paved the way for implements for killing prey. Which makes Pruetz's observations of chimps sharpening sticks and using them to whack bush babies all the more arresting: Fongoli's females seem to have skipped ahead to the killing tools. Barbecue tongs can't be all that far behind.

Pruetz and I are sitting along a forested ravine where the chimps rest during the day's hottest hours. The vegetation is thicker here. We watch a slender green vine snake move through the grass. Birds are calling over our heads. One says cheerio; one actually says tweet. A third says whoop whoop whoop whoop whoop, like Curly of the Three Stooges. (When I ask what that one is, Pruetz replies, not at all sarcastically: "a bird." She is a woman of singular interests.)

Pruetz directs my gaze to a tangle of saba vines. Where I see a dark mass, she is able to distinguish six animals. The woman has chimp vision. (It's a condition that lingers long after she gets back to Iowa. "I get home and I'm looking for chimps on campus.") The animals can be so well hidden and so quiet that even Pruetz has trouble finding them. She sometimes locates them by smell—"chimp" being a potent variant of B.O. "Yesterday I thought I smelled chimp," Pruetz says, "but it was me."

The scene in the vines is one of drowsy, familial contentment. Yopogon is grooming Mamadou. Siberut is leaning against a tree trunk, rubbing his two big toes together, as he often does. A pair of youngsters swing on vines, flashing in and out of an angled shaft of sun. One uses a foot to push off from a tree trunk, spinning himself around. The other swings from vine to vine, Tarzan-style. They are almost painfully cute.

A chimp called Mike lies on his back in a hammock of branches, legs bent, one ankle crossed atop the opposite knee. One arm is behind his head, the other is crooked at the elbow, the hand hanging slack from the wrist, in the manner of a cowboy slouched against a fence. We stare at each other for a full ten seconds. Partly because his pose is so familiarly human and partly because of the way he holds my gaze, I find myself feeling a connection with Mike.

I confess this to Pruetz, who admits to similar feelings. She cares about the Fongoli chimps as one cares about family. She sends excited emails when a baby is born and worries when the elderly and nearly blind Ross disappears for more than a week. But she does not reveal this side of herself at conferences. There it's all lingo and statistics, pairwise affinity indexes and "blended whimper pouts." "Especially with male chimp researchers," she says.

One of the first things primatology students are taught is to avoid anthropomorphism. Because chimps look and act so much like us, it is easy to misread their actions and expressions, to project humanness where it may not belong. For example, I catch Siberut looking toward the sky in what I take to be a contemplative manner, as though pondering life's higher meaning. What he's actually pondering is life's higher saba fruits. Pruetz points some out in the branches above Siberut.

Yet it is impossible to spend any time with chimpanzees and not be struck by how similar they are to us. I've been keeping a list of things I have seen or read or heard Pruetz say that drive home this point in unexpected ways. I had not known that chimpanzee yawns are contagious—both among each other and to humans. I had known that chimps laugh, but I did not know that they get upset if someone laughs at them. I knew that captive chimps spit, but I hadn't known that they, like us, seem to consider spitting the most extreme expression of disgust—one reserved, interestingly, for humans. I knew that a captive ape might care for a kitten if you gave one to it, but had not heard of a wild chimpanzee taking one in, as Tia did with a genet kitten. The list goes on. Chimps get up to get snacks in the middle of the night. They lie on their backs and do "the airplane" with their children. They kiss. Shake hands. Pick their scabs before they're ready.

The taboo on anthropomorphizing seems odd, given that the closeness—evolutionary, genetic, and behavioral—between chimpanzees and humans is the very reason we study chimps so obsessively. Some thousand-plus studies have been published on chimpanzees. As a colleague of Pruetz's once said to her, "A chimp takes a crap in the forest, and someone publishes a paper about it." (No exaggeration. One paper has a section on chimpanzees' use of "leaf napkins": "This hygienic technology is directed to their bodily fluids (blood, semen, feces, urine, snot). ... Their use ranges from delicate dabbing to vigorous wiping."

As for the chimps, they are not nearly as intrigued by the ape-human connection. While we've been observing them, they have largely ignored us, occasionally shooting a glance over one shoulder as they move through the brush. There is no fear in this glance, but neither is there curiosity or any sort of social overture. It is a glance that says simply, Them again.

Even Mike. He just turned away from my gaze and pointedly, or so it seemed, rolled over to turn his back on me. In hindsight I would have to say that the reason Mike had been looking at me was that I happened to be in his line of vision.

The chimps begin making their nests, breaking off leafy branches and dragging them into the treetops. Pruetz will wait until all are bedded down before turning to head back. We sit and listen to their "nest grunts"—soft, breathy calls that seem to express nothing more than the deep contentment one feels at the end of a day, in a comfortable bed.