What Do Monkeys Know?

It may depend on who's asking the questions

Psychologists have spent decades demonstrating the amazing abilities of animals. We now know, from lab experiments, that chimps can use blue triangles to represent red apples, and that dolphins can use general rules to decode sentence like series of hand gestures. Such experiments help illuminate what it means to be human, by showing where we part company from our cousins. Yet they never yield a full picture of an animal's mind at work. As the British zoologist Nikolaas Tinbergen remarked 30 years ago, "One should not use identical experimental techniques to compare two species, because they would almost certainly not be the same to them. "

The point has never been lost on Dorothy Cheney and Robert Seyfarth. When the couple started studying vervet monkeys back in the late '70s, they reasoned that minds, like other organs, are tailored to the demands of survival in natural environments. It followed that the best way to assess a creature's mental abilities was to watch what it does in its own habitat. So they hunkered down in the acacia woodlands of Kenya's Amboseli National Park and, over the span of a decade, gathered data on how Thinking a the vervets tackled specific survival-related problems. And as the evidence mounted, they drew careful inferences about what the monkeys know and how they think. In a new book called "How Monkeys See the World" (377 pages. University of Chicago Press. $24.95), the two primatologists tell their story. It's a fascinating intellectual odyssey and a superb summary of where the science stands.

Vervets are highly political creatures. How any two of them will interact depends on whether they're relatives, whether they belong to the same territorial group and, if so, which one enjoys higher social standing. They're also famous for having a well-developed system of vocal communication. They give audibly different alarm calls in response to their three most common predators-the leopard, the eagle and the snake-and each call elicits a specific response from listeners. In addition, they make specific grunts to mark various social acts, such as approaching a superior, approaching a subordinate or spotting members of another group.

Intriguing as they are, these phenomena offer only the vaguest clues about how the monkeys' minds work. Do vervets use abstract notions such as rank and kinship to order their experience? Do they form mental hierarchies, or simply learn through conditioning to behave differently toward different individuals? And how much deliberation goes into their calls? Bees exchange fairly detailed information about food sources through an involuntary reflex known as the waggle dance. Is vervet communication equally reflexive, or do the animals know what their calls mean? Cheney and Seyfarth devised myriad ways to explore such questions.

To see whether the animals grasp the concept of rank, the researchers analyzed grooming interactions. Vervets forge alliances by pairing off to groom one another-and because they all tend to pursue alliances with their superiors, the competition for grooming partners can be stiff. Finding a good back to scratch often requires breaking up a grooming session already in progress. If an intruder outranks one of the two groomers, the outranked monkey typically gives up its place. But suppose the intruder outranks both groomers, as sometimes happens. Who should defer?

Lacking the concept of a hierarchy, the two groomers would be equally likely to step aside, for each would perceive the intruder's rank only in relation to its own. But Cheney and Seyfarth observed 30 such instances, and in 29 of them the higher ranking groomer stayed put, leaving the subordinate to defer. "To do this," the researchers deduce, "she must not only know her own status relative to [the subordinate and the intruder] but also their status relative to each other. In other words, she must recognize a rank hierarchy."

Cheney and Seyfarth came up with an equally deft strategy for determining whether vervets consciously ascribe meanings to their calls. The trick was to create an opportunity for the animals to link one call to another one related in meaning. Vervets don't always use the same sound to signal the approach of a neighboring group; a casual sighting elicits a wrrr, whereas a closer, more hostile encounter brings an acoustically distinct call known as a chutter. What would happen, the two researchers wondered, if they started playing recordings of one vervets wrrr when there were no aliens in sight? What lessons would other group members draw? As expected, the animals quickly learned to ignore the unreliable wrrrs. But that wasn't all they learned. They also ignored chutters by the same animal even as they responded normally to all its other calls. Since wrrrs and chutters don't sound alike, one can only conclude that the vervets perceived them as carrying similar meanings.

There are, of course, important differences between monkeys and primatologists. Vervets' mental capacities seem not to extend much beyond the mundane business of staying alive. They may use calls to represent acts and objects, but there's no evidence that they can label classes of acts or objects. They don't refer to other vervets as "siblings" or "enemies," or communicate abstractly about concepts like friendship or danger. Humans are better at lifting insights out of one context to apply them in another: we're more aware of our awareness. But, as this book so vividly demonstrates, we're not the only creatures that think with concepts or communicate with symbols. Consciousness, it turns out, is not a human distinction. It's a feature of the natural world.