Inside Animal Minds: The New Science of Animal Intelligence (4 page)

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 with 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 that this scenario—a large crowd competing for limited resources—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 the 2007 “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 postdoc 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, and 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—for example, “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 United States, not Japan.)

No one around Fongoli is sending chimps to the optician, but locals do accord the animals a remarkable amount of respect. 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 20 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.