Self-awareness, in a cognitive context, refers to the capacity to direct attention inward and recognize oneself as an individual distinct from the surrounding environment and other beings. This is more complex than simple consciousness, which is merely being awake and responsive to the world. Self-awareness involves the understanding of one’s own body, thoughts, and emotions, and forms the basis for introspection and personal identity. Historically, this ability was considered a uniquely human trait, but the field of comparative cognition has shifted focus to systematically explore the inner lives of non-human animals. Scientists are now employing various behavioral tests to determine if other species possess this fundamental sense of self.
Testing Self-Recognition in Non-Human Species
The most widely recognized method for investigating self-awareness in animals is the Mirror Self-Recognition (MSR) test. The procedure involves placing an odorless, visual mark, such as a colored dye or sticker, on a part of the animal’s body that it cannot normally see, like its forehead or ear. This test determines if an animal recognizes its reflection as itself rather than another individual.
The animal is then given access to a mirror, and researchers observe its behavior. A “pass” is recorded if the animal exhibits mark-directed behavior, meaning it touches, investigates, or tries to remove the mark while looking at its reflection. This behavior suggests the animal understands that the image in the mirror is its own body, which has been physically altered.
Before the mark test, animals typically progress through earlier stages of mirror interaction. These stages start with social behaviors directed at the reflection as if it were another animal, followed by exploratory behavior, and then contingency testing. Contingency testing involves the animal performing repetitive movements to confirm the reflection is linked to its own actions. The final stage of using the mirror to examine a previously unseen body part is the primary evidence for visual self-recognition.
Beyond the MSR, other cognitive tests suggest a concept of self, such as complex tool use that requires a sense of one’s body in space, or metacognition tests. Metacognition, or “thinking about thinking,” is tested by observing if an animal expresses uncertainty or declines to answer when it is unsure of a task. This suggests an awareness of its own knowledge state and attempts to assess an animal’s understanding of its internal mental states.
Animals That Exhibit Self-Awareness
Only a small number of species have convincingly passed the MSR test. Among the most consistent passers are the Great Apes, including chimpanzees, bonobos, and orangutans. When first exposed to a mirror, chimpanzees often reacted aggressively, mistaking the reflection for a rival. They eventually began using the mirror for self-directed behaviors like grooming parts of their bodies they could not otherwise see.
Bottlenose dolphins have also demonstrated self-recognition. Researchers observed them engaging in repetitive head circling and close viewing of marked areas when presented with a mirror. This capacity is considered a case of convergent cognitive evolution, possibly related to their complex social structures and cooperation.
Asian elephants are another large-brained mammal to show this capability. In one study, a single elephant named Happy repeatedly touched the paint mark on her head with her trunk while looking into a large mirror. This mark-directed behavior confirmed that she recognized the reflection as her own body.
Self-recognition is not exclusive to mammals, as the Eurasian magpie became the first non-mammalian species to pass the test. Researchers placed a colored spot on the bird’s throat, which it could only see in the mirror, and the magpies immediately tried to scrape the mark off. This finding challenged the idea that the neocortex, a part of the brain found only in mammals, was necessary for this advanced cognitive skill. More recently, the bluestreak cleaner wrasse, a small tropical fish, has also been documented attempting to scrape off a colored tag after seeing its reflection.
Behavioral Evidence and Testing Limitations
The MSR test is not a perfect measure of self-awareness and carries an inherent bias toward species that are highly visual. Many intelligent animals that rely on other senses, such as olfaction or sound, fail the test, which does not necessarily mean they lack a sense of self. For example, dogs primarily use smell to navigate their world and recognize other canines, and their mirror reflection lacks the corresponding scent.
Researchers have proposed “olfactory mirror” tests for canines, involving the modification of an animal’s own scent to see if it elicits a reaction. Some studies show that dogs spend less time investigating their own scent compared to that of other dogs, indicating a form of self-other discrimination. However, this is still debated as conclusive evidence for self-awareness. In the aquatic world, highly intelligent octopuses also fail the MSR test, often reacting aggressively to their reflection as if it were a rival.
Octopuses are largely solitary and lack the social motivation to examine their own bodies visually, which is a major limitation of the test for them. Their complex behaviors, such as the ability to fluidly change their posture and body size, suggest a high degree of body awareness and control not captured by a visual mark test. The failure of many complex species to pass the MSR highlights the need for species-specific tests that cater to their unique sensory modalities. The current scientific view is that a failure to pass the visual MSR test should not be interpreted as a definitive absence of self-awareness.