Probing Primate Thoughts: Questions Arise about the Mental Lives of Apes and Monkeys

Article excerpt

In a series of popular children's books, Curious George, a monkey, lets his raging inquisitiveness lead him into all sorts of trouble. George knows when he has erred, though, and always makes amends. The puckish primate also senses that an inner world of thought and emotion pulses around him. For instance, George recognizes that the firemen coming through his door are angry with him for ringing the emergency telephone number, and on another occasion he tries to cheer up a sad-looking girl he meets in a hospital.

Scientists who suspect that real-life apes and monkeys maintain at least a modicum of Georgelike insight into mental lives-their own and others'-have received some setbacks of late. Recent evidence suggests that such mental feats may elude even our closest evolutionary relative, the chimpanzee. What's more, a widely recognized method for studying primate thinking may yield much fuzzier results than its proponents have contended.

The suspicion that nonhuman primates can to some extent discern motives, plans, and strategies behind observed behaviors won a number of converts during the past 25 years. Reports that apes could express themselves with simple languages invigorated this view.

In addition, researchers noted that chimpanzees and orangutans, like human toddlers, turn as curious as George when they gaze into a mirror and see themselves in an unexpected light. If an experimenter places dye marks or stickers on their faces and then puts a mirror in front of them, these creatures notice the decorative additions and proceed to use their reflected images to guide their touching of their own faces and then the rest of their own bodies.

Gorillas, on the other hand, tend to pay mirrors no heed. Monkeys react angrily to their own reflections, apparently mistaking them for competitors.

Mirror-wielding investigators generally concluded that self-awareness and a basic appreciation of what others may or may not know arise only in humans, chimps, and orangutans.

Critics now argue that what an ape or monkey does in front of a mirror provides a distorted view of their mental landscape. Some who see merit in the mirror test still doubt that self-awareness and a penchant for mind reading in social situations characterize any species except humans.

"In the last few years, I've become much more open to the possibility that chimps may not develop a mental understanding of themselves and others, at least not to the extent that preschool children do," remarks Daniel J. Povinelli, a psychologist at the University of Southwestern Louisiana in New Iberia. "You can train chimps to use a language, but it's unclear whether they understand themselves as mental agents or have a mental disposition toward that language."

The mirror test has served as the gold standard for establishing the presence of self-awareness in primates. Gordon G. Gallup Jr., a psychologist at the State University of New York at Albany, first reported its use in 1970.

Gallup's procedure consisted of applying brightly colored dye marks to the eyebrows and ears of anesthetized chimps that had become accustomed to seeing their mirror reflections. After the numbing medicine wore off, a video camera recorded the chimps' behavior in front of a mirror.

Dye-marked chimps stared at their reflections, touched themselves on the colored patches, and inspected the inside of their mouths and other body areas. In contrast, marked chimps who saw themselves in a mirror for the first time made no effort to inspect dye marks or any other physical features.

Animals that learn to use mirrors to monitor changes in their appearance and to examine their bodies possess knowledge of their own mental experience, Gallup argues. A creature displaying a self-conception of this type can take into account what others may or may not know, he says.

So far, Gallup's mirror procedure has consistently evoked self-inspection only from human children older than 18 months, chimps, and orangutans. …