Although we are the only species that closely examines our reflection every day, we are not the only ones who recognize ourselves in reflective surfaces.
Scientists have tested mirror recognition in a variety of animal species, starting with studies on chimpanzees (Pan troglodytes) published in 1970. Animals from ants to manta rays to African grey parrots (Psittacus sylvatica) were examined for signs of self-awareness when held up to a mirror. A small handful are found to be looking at themselves. Many are not. And some have exhibited inconclusive behavior.
These mixed results have led researchers to debate the usefulness of the test and its contribution to understanding animal cognitive abilities.
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“Many animals fail the test,” Frans de Waal, a primatologist at Emory University, told Live Science. De Waal has conducted self-awareness tests on capuchin monkeys – which failed. “They have to examine a visual marker in front of a mirror by themselves, without training or reward. It has to be spontaneous. Most of the claims in the literature don’t fit that description.”
So which animals passed the test?
In the 1970 chimpanzee experiments, four chimpanzees were anesthetized and their faces marked with red paint. When they woke up, they examined the marked areas in the mirror, indicating that they understood that they were seeing themselves.
The marking test is now considered the most conclusive evidence for mirror self-perception.
Other great apes have also passed the test. In a study from 1973, orangutans recognized themselves – and could even identify markings on their bodies.
A 1994 study observed that bonobos used a mirror to examine areas of their bodies that they could not otherwise see. The results for gorillas were less clear.
Monkeys normally view their reflection as another animal, but a series of controversial studies have shown that some species are able to identify themselves after extensive training programs.
This is also true for other animals, which raises doubts about the implications of these studies. “Does this training process negate the results of the mirror test for the species that need it?” wonders Ellen O’Donoghue, a cognitive psychologist at Cardiff University in the UK who has studied learning in pigeons. Critics of tests that use training exercises point out that such learned behavior is not reliable evidence of self-awareness.
Until recently, the only other land mammal to convincingly pass the test was an Asian elephant (Big Elephant) at the Bronx ZooHowever, a study published in January 2024 in the journal Neuron suggested that mice also seem to recognize changes in their own bodies in a mirror.
Studies on dolphins suggest that they can also recognize their own reflection. Study from 1995 with video instead of mirror and a Study from 2001 In both studies that used mirrors, it was noted that dolphins use the images from these mirrors to examine markings on their bodies.
In 2008, researchers studied Eurasian magpies (Pica-Pica) found the first evidence that non-mammals are capable of mirror self-recognition. Pigeons also have passed the test — but only after a rigorous conditioning phase. And in 2022, wild Adelie penguins (Pygoscelis adeliae) showed signs of mirror self-confidence However, they did not respond to the colored bibs that were placed around their necks to mark their bodies.
Tests on lower animals proved to be particularly controversial. A study from 2015 suggested that ants might have some self-awareness because they tried to remove blue paint from their heads when looking at their reflection. Two studies have shown that fish can recognize themselves. A 2016 study found that mantas appeared to examine themselves and blow soap bubbles when shown a mirror. However, no marking test was performed. And a Experiments 2019 on cleaner wrasse (Labroides dimidiatus) found that they tried to remove patches of color from their undersides after spotting them in a mirror. And in the 2024 mouse study, researchers found that mice removed patches from their bodies; those that could see the patches removed them, while mice that couldn’t see the patches because they blended with their fur color did not. The researchers even went a step further and scanned the mice’s brains as they removed the patches. They found that a subset of brain cells called ventral hippocampal CA1 neurons lit up during the mirror test. Whether a similar circuit plays a role in human self-recognition remains to be seen.
The fact that these supposedly more primitive organisms pass the mirror test, while some of the most intelligent non-human animals, including African grey parrotshave failed, has called its usefulness into question. It is unclear whether these studies demonstrate a true sense of self in the human sense or whether they merely indicate a differentiated body awareness.
“The mirror test can reveal one aspect of self-confidence,” O’Donoghue told Live Science. “There’s a tendency to think of self-confidence as an all-or-nothing thing. That’s probably not true. It’s probably more of a gradation.”
Editor’s note: This story was updated at 2:20 p.m. EDT on Friday, June 28, to reflect that mice pass the mirror test.
