The computer randomly splashed numbers 1 through 7 about the screen. When Ai touched the number one, white blocks covered the other numbers. She then had to touch the white blocks in the correct numerical sequence to receive a treat, a small chunk of apple. The odds of correctly guessing the sequence are 1 in 5,040. Ai made many mistakes with seven numbers, but she succeeded almost every time with six numbers, and the odds of that happening by chance are 1 in 720 tries.
Ayumu’s success rate, like those of other chimps younger than about 10, is better that Ai’s. It appears that young chimps, like human children, have better so-called eidetic memory—the ability to take a mental picture of even a complicated image—than their elders. And chimps outperform humans.
I once watched Matsuzawa show videos of his experiments with Ai and Ayumu at a conference attended by the world’s leading chimp researchers, including Jane Goodall, Christophe Boesch, Frans de Waal and Richard Wrangham. The audience gasped, oohed and aahed at the chimps’ memory skills.
Ayumu next began doing a word-comprehension test known as the color Stroop task. Like his mother, he has learned that certain Japanese characters correspond to different colors. He can touch a colored dot and then touch the word for that color. But does he understand the word’s meaning or has he just learned that when he connects this symbol with that one, he receives a treat? A dog, after all, can be taught to put a paw into a human’s hand and “shake,” but, as far as we know, it has no idea that shaking hands is a human greeting.
To test whether the chimps understand the meaning of words, researchers miscolor some of the words—showing, for example, the word “black” printed in the color red—and challenge Ayumu to identify the color of the word, not the word itself. Matsuzawa asked to borrow three writing pens of different colors: black, blue and red. He then wrote the English words for the colors in a variety of inks. He asked me to tell him, as quickly as I could, the colors in which the words were written. As he expected, I slowed down, and even stumbled, when the colors did not match the words. “The bottom line is it’s hard to read ‘red’ in blue ink and say it’s blue because you understand the meaning of the words,” he said. Basically, when I saw red, I pictured the color red and had to block that knowledge, which takes a fraction of a second, to say “blue.”
He then changed the words to Japanese characters, which I do not understand. This time I had no trouble rattling off the colors. In the Stroop test, if the chimpanzees actually understand the meaning of the words for colors, they should take longer to match, say, the word “blue,” when colored green, to a green dot. So far, Matsuzawa told me, preliminary data suggest the chimpanzees do, in fact, understand the meaning of the words.
Captive chimps have long been taught sign language or other communication techniques, and they can string together the symbols or gestures for words in simple “Me Tarzan, You Jane” combinations. And, of course, the animals use pant-hoots, grunts and screams to communicate. But in decades of ape language experiments, the chimpanzees have never demonstrated a human’s innate ability to learn massive vocabularies, embed one thought within another or follow a set of untaught rules called grammar. So yes, chimpanzees can learn words. But so can dogs, parrots, dolphins and even sea lions. Words do not language make. Chimpanzees may well routinely master more words and phrases than other species, but a 3-year-old human has far more complex and sophisticated communication skills than a chimpanzee. “I do not say chimpanzees have language,” Matsuzawa stresses. “They have language-like skills.”
Despite Matsuzawa’s precision, some people in the field caution that his experiments can fool us into granting chimpanzees mental faculties they do not possess. Other researchers found that they could perform as well as Ayumu on the numbers test if they practiced enough. And while no one disputes that Ai can sequence numbers and understands that four comes before five, chimp researcher Daniel Povinelli of the University of Louisiana at Lafayette says that feat is misleading. Unlike young human children, Ai, Povinelli contends, doesn’t understand that five is greater than four, let alone that five is one more than four. Ai—in Povinelli’s estimation “the most mathematically educated of all chimpanzees”—has never had that “aha” moment.
As fascinating as it is to watch Ai and Ayumu working the touch-screen computers, I was even more struck by Matsuzawa’s interactions with the animals. Once, watching Ayumu, I leaned against the Plexiglas to take some photographs. I was not using a flash and thought I was being discreet, almost invisible. But Ayumu jumped up, stretched his arms in display, smacked the Plexiglas and spit at me. He stood just inches from my face. “Stay right there, please,” Matsuzawa said to me. I was completely safe, but still frightened by Ayumu’s raw power.
As I sat frozen, trying not to react to the serious stink-eye from Ayumu, Matsuzawa slipped a jumpsuit over his clothes and a pair of thick gloves over his hands. With his race car attire in place and what looked like a bathroom scale tucked under one arm, he headed toward an entrance to the chimp enclosure. His staff hit buzzers, and a series of metal gates groaned open, allowing him to enter the booth.