Monkeys Can Learn to Recognize Themselves in the Mirror

Generations of monkeys had tried and failed a classic test of intelligence, but the fault may have been in the way humans thought of the test

monkey mirror.jpg
Neng Gong and colleagues/Current Biology 2015

When London’s Zoological Garden acquired a female orangutan named Jenny in the 1830s, the keepers there taught her to eat with a spoon and wear a dress. Apparently, those trappings only served to convince most people that apes were nothing like humans. But a young Charles Darwin thought differently, writes science journalist Carl Zimmer in his book The Descent of Man. Darwin wrote to his sister that Jenny clearly understood a keeper’s admonishment to "stop bawling and be a good girl" in order to get an apple. He also noted how Jenny would look at herself in a mirror.

That self-recognition became the basis for a test of intelligence. Gordon Gallup, Jr., marked individual chimpanzees with a red dye and put a mirror in their cage in the 1970s. The chimps quickly learned to recognize themselves in the reflection and investigate the marks—above the eyebrow ridge or on the tip of their ears, out of sight without the aid of a mirror. Since then, we’ve determined that bonobos, orangutans, gorillas, dolphins, elephants and magpies can also pass the self-recognition test.

Humans can too, of course, usually by 2 years old. But Gallup himself noted that monkeys cannot. Turns out, they just weren’t given enough of a chance.

This time, researchers shined a high-powered laser on a rhesus monkey’s face in front of a mirror. It was enough to cause some kind of sensation that made the monkey reach up and touch the spot. Later, a lower-powered laser that couldn’t be felt also earned a response.

All that can be chalked up to the monkey learning that a red spot on the "other" monkey’s face means you should touch your own, especially since the monkeys were rewarded with food. So, as an additional step, the researches observed the monkeys in a cage with a mirror. The trained monkeys would get close to the mirror, check their own bodies (as with all monkeys, much of this investigation was related to their genitals) and pull their face or head hair. Non-mirror trained monkeys didn’t have the same behavior. The difference lasted at least a year. The researchers published their findings in Current Biology.

"Our findings suggest that the monkey brain has the basic 'hardware' [for mirror self-recognition], but they need appropriate training to acquire the 'software' to achieve self-recognition," says Neng Gong of the Chinese Academy of Sciences, one of the study authors, in a press statement.

Perhaps the marks just didn’t interest the monkeys enough to spur the realization that the reflection is "me." Instead, they needed some help, a little heat on the face, a little treat as a reward. 

Researchers use self-recognition in the mirror as a proxy for the brain’s ability to conceive and process the idea of self. In some people, that ability is impaired—people with schizophrenia and Alzheimer’s, for example, can be unable to recognize themselves in a mirror. The study brings up the possibility that some kind of training might be useful for helping people with those conditions. "Even partial restoration of self-recognition ability could be desirable," the researchers write.

Also, the test itself might deserve an update: In a 2006 experiment with elephants, only one passed the mark test, but the other two behaved in a way that indicated recognition of themselves, such as making repetitive movements, writes Maggie Koerth-Baker for Scientific American. The fact that kids from Fiji and Kenya take longer to pass the test indicates that it might not be perfect. Much of it relies on the subjects' interest in what that mark might be. "[E]lephants are different" than humans, says Joshua Plotnik, the researcher who tested the three animals. "They're huge and they're used to putting things on, not taking things off of their bodies, like mud and dirt."

Maybe the monkeys felt the same way, until they were trained to think differently.

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