Source: New York Times
Date: 26 July 2005

Who's That Strange Monkey in the Mirror?


Humans, the great apes and, probably, dolphins share an intellectual skill unusual in the animal world: they recognize their own reflections in a mirror.

That ability seems to mark a bright line between these species and monkeys, who, scientists have long assumed, look into mirrors and see only strangers. But a monkey's reaction to its reflection is more complex than is generally assumed, said Frans de Waal of the Yerkes National Primate Research Center in Atlanta.

Dr. de Waal and his colleagues were able to test the widely held belief that monkeys see strangers in the mirror using two troops of tufted capuchin monkeys at the Yerkes Center that had never met each other.

The capuchins, the Yerkes team is reporting today, understood at once that the mirror image was not a stranger, even though they failed to recognize themselves in the image. The findings appeared last week in The Proceedings of the National Academy of Sciences.

The female capuchins, the researchers found, avoided eye contact with a strange monkey while also making friendly overtures. But in front of a mirror their behavior was different. They looked often at their image, almost as if trying to flirt with it.

The male capuchins, in contrast, were seriously bothered by their image. Unlike Narcissus, they "appeared confused and distraught by their reflections" and often tried to escape from the testing room, the Yerkes team reports.

So what is going on in the monkeys' minds?

One possibility is that the image in the mirror is assigned to a mental category of "Puzzling Other," the researchers say. The male capuchins, particularly the high-ranking ones, may be discomfited by their reflection because it fails to play by the rules of the monkey hierarchy and show them due deference. On the other hand, this realization might be expected to build up gradually in the minds of the male monkeys, making it hard to explain why they instantly perceive that the image is not a stranger.

Human infants learn to recognize themselves in a mirror at 18 to 24 months, but they acquire an understanding of mirrors before that. Give a female chimp a mirror, and one can have no doubt she knows just what it is for.

The chimp will look at the two important parts of her body that she can usually never see, Dr. de Waal said. One is the inside of her mouth; the other is her rear end.

Mirror self-recognition is often regarded as a touchstone of self-awareness. But every animal must have some sense of self, for example in calculating its weight when grasping or sitting on thin branches.

Self-recognition, Dr. de Waal said, may tap into a higher sense of self. But there also may be a spectrum of self-awareness, with the capuchin's version falling short of the chimp's but above that of species that fail to recognize themselves. For example, the capuchin's understanding of mirrors is more advanced than that of male robins, who will ceaselessly attack the intruding male they see reflected, or that of cats and dogs, which will ignore a mirror once they have established there is nothing behind it.

Male capuchins probably react differently from females because they take their mirror image more seriously and don't know how to handle it, Dr. de Waal said. But both sexes seem to possess a greater understanding of the illusory qualities of mirrors than is generally assumed.

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