Mirror Testing: Which Animals Demonstrate Visual Self-Recognition?

The mirror self-recognition (MSR) test or mark test is a classic test that involves placing a colored mark on an animal's body, then showing the animal the reflection of their marked body in a mirror, and observing the animal's reaction.

If the animal tries to remove the colored tag or mark from their body, the mirror test shows they recognize their own reflection.

Many people have no trouble intuitively believing that fellow big-brained mammals (and often their smaller-brained buds in the case of beloved household pets) exhibit some signs of consciousness.

But when it comes to non-mammalian species like fish, insects and worms, those same people often waver when considering whether they, too, exhibit anything close to resembling consciousness.

Some consider self-recognition a herald of self-awareness. Self-awareness is a state that can denote introspection, personal identity and humanlike levels of consciousness.

In human development, many consider children self-aware once they have the cognitive ability to recognize their own faces in a mirror. Human children recognize themselves in the mirror test around 18 months of age.

Early research revealed that, like humans, some members of the great ape family can recognize their own reflections in mirrors, and for decades, it was assumed that was the extent of it. But when the classic mirror test was tailored to better suit the specific characteristics of dolphins and elephants, it was found that they, too, exhibit signs of self-recognition.

In the case of dolphins, researchers developed a test for them to indicate interest in a mark without hand gestures, and with elephants, their level of interest was examined when mirrors large enough for them to see their entire bodies were placed inside their habitats.

Perhaps more surprisingly, due to the even greater evolutionary divide, some species of birds and fish have evolved the capacity for self-recognition. A 2008 study found that magpies also try to examine strange markings indirectly placed beneath their beaks when set in front of a mirror.

In 2019, the cleaner fish (Labroides dimidiatus) passed a modified mark test. This tiny fish exhibited a scraping behavior when it saw in its reflection a colored tag on its body [source: Kohda]. This study raised questions about whether self-recognition, such as in the mirror test, is an accurate measure of self-consciousness.

A 2023 review of 50 years of animal self-recognition studies of found that, so far, only social animals exhibit self-recognition [source: Lei].

These animals have passed mirror tests in at least two separate studies without prior training:

These other animals have passed the mirror test just once or have had controversial results:

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