Monkeys Join Short List of Animals Who Can Recognize Themselves in the Mirror

Self-awareness -- an ability to recognize one's individual self as separate from others -- is a quality humans possess that not all species do. Mirror recognition tests show that there's actually a very short list of animals that can recognize themselves in the mirror: great apes, dolphins, Asian elephants and Eurasian magpies, according to a report from Science Magazine. The newest member of this exclusive club? Rhesus monkeys.

A study published in the Proceedings of the National Academy of Sciences revealed that rhesus monkeys can be taught to recognize themselves in mirrors, which is an important part of cognition.

In the mirror self-recognition test, a colored, odorless mark is placed on an animal's head or shoulder, then it's directed in front of a mirror. If the animal sees and rubs the mark, it means it has passed the exam and recognized its reflection as itself. It's believed this indicates a certain understanding of the "self."

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Previous tests have shown that some animals (i.e., dogs and cats), when subjected to the exam, are unable to innately recognize themselves in mirrors. However, they can use the mirror to find food. This new study attempts to bridge the gap between simple mirror use and recognizing one's self, and they used rhesus monkeys in their observations.

The scientists, led by Mu-ming Poo and Neng Gong, subjected three monkeys to intensive training, which included being placed in front of a mirror and pointing a red laser dot at random spots nearby, sometimes at a spot the monkeys can only see through the mirror. The animals were rewarded every time they touch the laser dot.

After a few weeks of training, the three rhesus monkeys were given the mirror self-recognition test again, which they passed easily. Their behavior clearly indicated that they recognized their own reflections as they inspected their genitals, combed their hair and looked at their teeth. Meanwhile, three other untrained monkeys did not display any of these actions.

This suggests that there might be more animals who are self-aware than the results of the mirror test would indicate. Some animals, like the rhesus monkey, may not have the innate ability to recognize their reflections, but they have the ability to learn.

However, it doesn't necessarily mean that the test is now ineffective, explained Lori Marino. Marino, who is not part of the study, is the executive director of the Kimmela Center for Animal Advocacy and a former faculty member in neuroscience and behavioral biology at Emory University.

"This study in no way 'debunks' the validity of the mirror self-recognition test," she told Gizmodo. "The researchers may have uncovered some factors that are responsible for the difference between some species 'passing' the test and some species 'failing' the test."

She added, "Passing the test means there is a level of self-awareness that is similar to other species who pass the test," she says, "But 'failing' the test by no means indicates lack of self-awareness."