Ayumu came right over to him. “Sit,” commanded Matsuzawa, in English. “Be good boy.” He pointed to Ayumu and also spoke to him in Japanese. Ayumu took a seat.
Matsuzawa and Ayumu played a nonverbal imitation game, with the chimp touching his lips, patting his head and opening his mouth in response to Matsuzawa’s cues. At one point, when Ayumu realized he was not going to get a treat, he jumped up, and I was convinced he was going to bite Matsuzawa. But Matsuzawa slapped his back and took control, bulleting him with commands to sit, lie down and even climb the wall, each of which Ayumu dutifully obeyed. Then they rolled around on the ground together, wrestling, until Matsuzawa, tired, just flopped into a prone position and rested. When they were done playing, Matsuzawa weighed Ayumu and checked his teeth. He then turned and did the same with Ai. He wiped the floors with paper towels to collect samples of their urine, which he’ll use to study hormonal levels. “For 30 years I’ve been with chimpanzees in the same room, and I still have ten fingers,” Matsuzawa deadpanned.
In addition to running the institute for the past four years, Matsuzawa has operated a field station in Bossou, Guinea, since 1986, where he studies wild chimpanzees. In the primatology world, he is viewed as a top investigator. “Tetsuro Matsuzawa is sui generis, a unique primatologist who studies chimpanzees both in captivity and in the wild, generating rigorous, fascinating and important data about our closest evolutionary cousins,” says evolutionary biologist Ajit Varki of the University of California at San Diego. “Unlike some others in the field, he also has a refreshingly balanced view of human-chimpanzee comparisons. On the one hand he has revealed some remarkable and unexpected similarities between the species—but on the other, he is quick to emphasize where the major differences lie.”
At his field site in West Africa, he has studied everything from the animals’ social dynamics to their feces (to understand the microbes that live in their intestines). He has focused on a capability that many researchers believe highlights a core difference between chimps and us: how they learn to use tools.
To crack nuts, chimps set up a stone anvil, place a nut on it and then smash it with a second stone used as a hammer. Matsuzawa, his former postdoctoral student Dora Biro of Oxford University and others have found that wild chimpanzees at Bossou do not teach the complicated behavior. The definition of “teaching” is a bit fuzzy, but it requires that three basic conditions be met. The action must come at some cost to the teacher. There must be a goal. And the teacher must use some form of encouragement or disapproval.
In Bossou, younger chimpanzees learn how to crack nuts simply by watching. This “master-apprenticeship” education, which Dutch primatologist Frans de Waal has compared to the way students learn to cut sushi after years of observing master chefs, means that chimpanzee adults do not reward their young when they do something the right way or punish them when they make a mistake. The young learn through trial and error.
Chimps eat nuts wherever they find them and wherever they have stones handy, which can make observing the behavior a matter of luck—especially in the forest, where it is often hard to see beyond a few yards. So in 1988 Matsuzawa created an outdoor laboratory in Bossou that has allowed his team to watch hundreds of hours of nut-cracking at close range. For a few months each year, the researchers place numbered stones of specific weights and dimensions on the ground and provide the chimps with piles of oil palm nuts. Then they hide behind a grass screen and watch the site from dawn to dusk, videotaping all chimpanzee visits. If teaching occurred, they would likely have seen it.
(There is some evidence of wild chimpanzees teaching nut-cracking in Tai National Park in the Ivory Coast. As Christophe Boesch’s team looked on, a chimp mother repositioned a nut on an anvil for her son; in another case, a young chimp handed a hammer to her mother, who rotated the stone into a different position. But it’s not clear that these actions came at a cost to the mothers, and the behavior occurred only twice in nearly 70 hours of observations of various chimp mothers cracking nuts with children present.)
Matsuzawa and his colleagues have documented other types of tool use: the chimpanzees fold leaves to scoop water, fashion a wand from a grass stem to retrieve algae from a pond, dip for ants or honey with sticks and use a pestle to pound the crown of an oil palm tree to extract something similar to heart of palm. Fifty years ago, when Jane Goodall first documented chimpanzees’ use of tools, it turned dogma on its head, as many anthropologists had argued that this activity was the exclusive domain of humans. Today, it’s less the tool use itself that interests chimpanzee researchers than the many variations on the theme, and, more importantly, how the animals transmit their skills from one generation to the next. In all the cases of tool use they have studied, Biro says, “we’re not seeing any examples of active teaching.”
Matsuzawa wants to understand more than what chimpanzees know and can learn. His studies repeatedly bump up against the dividing line that separates us from them, revealing sometimes astonishing differences that ultimately clarify what makes chimps chimpy and humans human. We’re both social creatures, we both communicate and we both pass on customs, but humans clearly are more advanced in each of these realms. Matsuzawa says he’s hunting for nothing less than “the evolutionary basis of the human mind.”