For an item that most of us use every day without much thought, mirrors can be a rich source of insight into the inner workings of our minds.

Self-awareness is something we consider to be a hallmark of the human experience. It represents the ability of an individual to recognize where they begin and where they end. Self-awareness means that a subject can conceptualize and experience their own personality and individuality. Understanding one’s body and mind as a distinct entity from the outside world, and recognizing different aspects of the self including traits, behaviors, and feelings, are all the purvey of self-awareness.

Mirrors are a great facilitator of self-awareness. By allowing individuals to look upon themselves directly, they can help convey that we are distinct entities in and of ourselves. But, while they can help in this regard, they can’t do all the work for us. As such, the mirror self-recognition test is considered the gold standard when determining whether an animal or individual possesses self-awareness.

The usual approach is to add a novel physical feature to a subject’s body (such as a dot of paint) and check whether they react in an unusual way to it. If the subject does, it suggests they can understand that they’re seeing a reflection of themselves (visual self-recognition) and an element that is not part of themselves (the paint). Therefore, they are self-aware.

But why are some species seemingly capable of self-awareness while others aren’t? And what does that mean, for us? Could the mirror test help us finally find other sentience on the planet with which to share our wonderful, if lonely, blue dot?

What we know so far

The mirror test was developed in the 1970s for the express purpose of checking whether non-human animals can recognize their selves. This was determined by observing how the subject would react to seeing itself in the mirror in its normal state compared to when a visual mark was placed on its body. If the reactions to the mirror differ significantly — if the animal exhibits ‘strange behavior’ when wearing the mark — that is a pretty reliable indicator that it can recognize itself.

Animals that pass the mirror test tend to either shift positions to allow them a better look at the mark on their body or try some type of action meant to touch or remove the mark. At the very least, they show increased scrutiny and are particularly attentive to the part of their body that bears the mark.

When animals who exhibit mirror self-recognition (MSR) are exposed to their reflection in a mirror, what generally happens is a progression through four behavioral response stages. These are the ‘social response’, in which the animal will treat their reflected image as they would a new individual. ‘Physical inspection’ follows, where the animal performs behaviors such as touching the mirror or looking behind it. Then come repetitive mirror testing behaviors (during this step the animal observes the image matching its movements) which lead to the ‘realization’ that they are seeing their selves.

It’s also worth keeping in mind that not all subjects of a particular species always pass the test, even if others do. But if a significant part or a majority of the animals belonging to a single species pass the test, then that species as a whole is considered to be self-aware. There are currently 9 species that are well-known to pass the mirror test and a few likely candidates that still need some testing to help us be sure. Those 9 species are:

Asian Elephants

In a 2006 study, researchers worked with three Asian elephants (Elephas maximus), one very large mirror, as well as visible marks and invisible, control ‘sham marks’ were applied to the animals’ heads.

The team explains that one particular advantage when performing MSR tasks with elephants is that “they can touch most of their own body with their trunks, thus permitting an unequivocal mark test”.

All three elephants lacked social displays with the mirror image, while all three showed investigative behaviors of the mirror. Their overall behavior was quite exciting to see.

“All three elephants displayed behavior consistent with mirror-testing and self-directed behavior, such as bringing food to and eating right in front of the mirror (a rare location for such activity), repetitive, non-stereotypic trunk and body movements (both vertically and horizontally) in front of the mirror, and rhythmic head movements in and out of mirror view; such behavior was not observed in the absence of the mirror,” the team explains.

“On more than one occasion, the elephants stuck their trunks into their mouths in front of the mirror or slowly and methodically moved their trunks from the top of the mirror surface downward. In one instance, Maxine [one of the elephants] put her trunk tip-first into her mouth at the mirror, as if inspecting the interior of her oral cavity, and in another instance, she used her trunk to pull her ear slowly forward toward the mirror. Because these behaviors were never observed in T1 or T2 (the initial, “no mirror” control conditions), or at any other time, they indicate the elephants’ tendency to use the mirror as a tool to investigate their own bodies.”

During trials with the marks, the elephants showed no interest in the control sham marks.

As for the experimental mark, one of the elephants showed increased interest (as measured by touching) of the marked area, and no interest upon further marking attempts. Although this may seem like a low success rate, the team explains that it is consistent with results from chimpanzees, where only around half of individuals pass the test and generally lose interest in the markings quite rapidly and show no great concern for repeated markings.

Great Apes

Several species of great apes have passed the mirror test, including bonobos, chimpanzees, orangutans, and gorillas. As mentioned in the last point, however, it’s not uncommon to see many individuals fail the test — especially very young or very old individuals.

One study from 1994 that worked with 9 bonobos (Pan paniscus) found that the apes exhibited “considerable interest in the mirror”, with at least 4 using the mirror to inspect parts of their bodies that were otherwise not directly visible to them — all reliable evidence that the species is capable of self-recognition.

The 1970 study that started it all, run by the inventor of the mirror tests himself, Gordon Gallup, found that chimpanzees (Pan troglodytes) also can recognize themselves in the mirror. The behavioral changes seen during the 10-day study suggest that the animals are not initially aware of their own appearance but that they can “learn to recognize themselves; i.e., that they had come to realize that their behavior was the source of the behavior being depicted in the mirror”.

When marks were used in a similar way to the elephant study above, the chimpanzees would look at their reflection in the mirror and use it to inspect the marks and guide their fingers to them. In addition to looking at the marks and their fingers repeatedly after touching them, some of the chimps even smelled their fingers.

Gorillas, however, seem to make a discordant note here. Among all great apes, they are the only tested species that could not consistently demonstrate the ability of self-recognition. One study published in 2022 concludes that “it might be suggested that, in general, gorillas do not show compelling evidence of MSR.”

Bottlenose Dolphins

Bottlenose dolphins (Delphinus truncatus) show some of the greatest levels of interest in their own reflections among all wild animals. And there is a lot of evidence to suggest that they recognize their reflection in the mirror.

One study from 1994 reports on an experiment with 5 dolphins aged 6-14 years old, who were living in captivity at Sea Life Park, Hawaii. This included several control situations (mirror without mark, no mirror, and no mark) and included a series of “new tests for self-recognition, tailored for dolphins rather than primates”.

The team explains that there was considerable variation in the dolphins’ reactions to the mirror. They recorded “a brief period of heightened tank activity shortly after the marks were applied” to two of the dolphins; this consisted of all four dolphins engaging in “fast, circular swimming for 2 min”.

The animals’ behavior suggested that all five dolphins examined their markings during the mirror test and all of them played with objects in front of the mirror, which is “suggestive of self-examination”. Although each dolphin exhibited unique behaviors in front of the mirror, they were all displaying obvious interaction with the mirror, “utilizing [it] in various ways”.

Orca Whales

Orcas (Orcinus orca) also known as killer whales are close relatives of the dolphins — in fact, it is the largest member of the oceanic dolphin family. As such, they share in the high intelligence that their kin are famous for.

A study published in 2001 found that both killer whales and false killer whales responded to the mirrors by displaying “contingency checking behaviors” — in essence, checking if their motions matched what they were seeing in the mirror. This implies that they must have some awareness of its position and understand the correspondence between the reflection and their bodies.

“Killer whales and false killer whales, like bottlenose dolphins, appear to possess the cognitive abilities required for self-recognition,” the authors explain, adding that their behavior in front of the mirror was different from what they would show in a social setting. “Most of the mirror-induced behaviors in the killer whales were visually striking: blowing air bubbles, rhythmic head movements, sticking the tongue out (and often moving it), playing with fish, and they were unusually frequent and lasted longer compared to these behaviors in social interaction. No affiliative (rubbing the body against a conspecific’s body for example), sexual or aggressive behaviors were observed when the animals were facing their mirror image.”

California sea lions, the same study adds, showed much shorter interest in the mirror than other cetaceans and thus it remains unclear whether they can pass the mirror test. While they did show some new behaviors in front of the mirror, they interacted socially in front of the mirror.

“Old male sea lion did not show much interest in the mirror, while the young female showed some. In general, unlike dolphins and killer whales, they did not display rhythmical head movement and they did not bring any objects to the mirror, they did not blow rhythmical bubbles and they did not play with them. But the sea lion data were collected for only a short period of time, so the probability of observing any given behavior in the sea lions was low”, the paper concludes.

Eurasian Magpies

So far, all of the animals on this list have been mammals — it’s time we change that up. Luckily, the next animal is the Eurasian magpie (Pica pica), also known as the common magpie.

A study from 2008 found that marked magpies who see their reflection in a mirror will attempt to remove the mark from their bodies, implying that the birds can understand that the image reflected by the mirror is not another individual, but themselves. The findings were further supported by the fact that magpies marked with invisible stickers did not attempt the same behavior when in front of the mirror.

The results on non-mammalian species are especially important in context. They offered us the first hints that self-recognition abilities are not produced by the neocortex, as previously believed. This part of the brain is tasked with handling higher-order cognitive functions and is unique to the mammalian brain.

It might be true that in mammals, self-recognition processes do actually arise in the neocortex. But magpies are birds and lack a neocortex, so their passing of the MSR invalidated the theory that only the neocortex — and thus, only mammals — can handle MSR.

While the previous experiment with magpies made us take a new, hard look at what we believed we knew about the emergence of self-recognition abilities in the brain, work with ants would force a paradigm shift.

Back in 2015, researchers in Paris found that ants would “behave otherwise [when seeing their reflection in a mirror] than when in front of nestmates seen through a glass”. The unusual behavior they displayed included rapid movements of their head and antennae to the left and right, touching the mirror, moving at different distances to the mirror while remaining attentive to it, and even sometimes grooming or cleaning their legs and antennae.

When in front of the mirror, ants marked with blue marks on the clypeus (essentially their foreheads) tried to clean themselves; those marked with a dot that was the same color as their cuticle did not. Similarly, ants marked with a blue dot on their occiput (the back of the head) did not attempt to clean themselves.

The team further reports that the presence of a blue dot on an individual’s clypeus induced aggressiveness in nestmates, while other kinds of markings did not. They add that very young ants did not show this kind of behavior when placed in front of mirrors.

The team did note that more work is needed to validate the findings, especially with ant relatives that have excellent visual perception.

That being said, such findings do turn our understanding of self-awareness and self-recognition on their head. It seems very probable that ants, despite their diminutive brains, limited complexity, and low cognitive capacity, are able to recognize their own selves in mirrors. This goes against everything that researchers assumed about such abilities in the past, most keenly the assumption that sizable brains and ample intelligence are needed to pull it off.

They also note that the ants’ ability to recognize their own reflection doesn’t necessarily imply any level of self-awareness — which leads us neatly to the next point.

The multiple layers of self-awareness

According to The Philosophy of Animal Minds by Robert W. Lurz, a Professor in the Department of Philosophy at Brooklyn College, CUNY, the most basic level of self-awareness is bodily self-awareness. In essence, this involves the recognition of one’s body as “importantly different from the rest of the environment”. This includes proprioception, an awareness of the body, its different parts, their movements and positions, and the awareness of various sensations that inform about the body’s state — pain, hunger, cold, itching, or tactile pressure, to name a few.

In Prof. Lurz’s own words, this facet of awareness is “essential to any creature that can feel features of its body and environment and act appropriately in response”, allowing them to move and act in the world around them. As such, he “somewhat radically [suggests] that most or all sentient animals have this type of self-awareness.”

What Prof. Lurz is talking about here is ‘consciousness’ — being aware and responsive to one’s body and environment. For the most part, people can intuitively recognize consciousness when they see it. We know that an oak sapling isn’t conscious because we can poke at it and it won’t move away. A hamster would; it will also rummage for food when hungry and scream at us if its bowl needs filling up.

Self-awareness is a process that builds one step above consciousness. This is the recognition of consciousness. The understanding that we not only exist, think, and feel, but that we are aware of our own existence and its associated processes.

While consciousness can be a fluctuating trait — someone receiving heavy sedatives such as anesthesia, for example, can go in and out of consciousness — self-awareness is, to the best of our knowledge, more stable. It’s not something one can lose temporarily. That being said, it’s not something we’re born with, fully, either: past research with mirror recognition tasks suggests that humans begin to exhibit reflective self-awareness sometime between 15 and 18 months of age.

What do the mirrors actually show?

The mirror test is today’s gold standard when trying to determine whether a particular species is capable of recognizing itself. As we’ve seen, the ability to do so is an important part of self-awareness — but can it, by itself, be considered proof of self-awareness?

Daniel Povinelli believes that it cannot. He is a Professor of Biology at the University of Louisiana at Lafayette and has spent years studying higher-order cognitive functions in great apes and humans. In an interview with NPR, he explains that it is very likely that self-awareness is more like a spectrum than a yes/no proposition. Animals like chimps that show great results with mirror tests may simply have a more sophisticated sense of “higher-order cognitive functions in great apes and humans”.

They may well be able to use mirrors as a tool to examine their bodies without necessarily understanding that they are seeing themselves. It is also possible that we’re reading too deeply into the results, looking for answers that we wish were there. We cannot rule out the possibility that, in our desire to better understand our own minds and our own subjective experience of life, we’re keen to grasp at any sign that our theories and assumptions are correct.

“When a test comes along that is dressed up in scientific garb like a mirror and then a mark and we’re in a scientific laboratory, we immediately want to point to this as confirmation of what we thought we knew all along,” he explains. “With respect to the mirror test, the million-dollar question about it is always: What is the chimp thinking about when it interacts with its own mirror image?”

One of the most surprising recent studies regarding MSR tests involved the cleaner wrasse (Labroides dimidiatus). This highly-social, reef-dwelling species was found to be able to recognize itself in the mirror — definitely an impressive feat for a fish that grows to around 10 cm in length. Alex Jordan, an evolutionary biologist at the Max Planck Institute for Ornithology in Germany and one of the authors of that study later explains in an interview for Quanta that his findings support the idea of self-awareness as a spectrum — and that the mirror test when used by itself is an imperfect measurement of a concept that is as complex as it is elusive of rigorous definition.

“I am the last to say that fish are as smart as chimpanzees. Or that the cleaner wrasse is equivalent to an 18-month-old baby. It’s not,” Jordan said for Quanta. “The mirror test is probably not testing for self-awareness”.

“I think the community wants a revision and a reevaluation of how we understand what animals know.”

The results of the wrasse study are undoubtedly fascinating. There’s just something extremely exciting about finding out that even an animal as tiny as seemingly simple as a wrasse is capable of something that we, ourselves, experience for most of our lives.

But as Jordan himself points out, recognizing yourself in a mirror isn’t the same thing as being self-aware, or being capable of higher thought. It doesn’t even mean that the fish experiences this mirror recognition the same way we do. “Just because the fish can respond to an unusual mark reflected back at it in a mirror doesn’t mean it can also contemplate philosophy,” Quanta quips.

In the end, the issue of animal self-awareness remains a very muddy business.

We haven’t yet agreed on a reliable, stable definition of what terms like consciousness, cognizance, and self-awareness mean — or how they could and should be measured — even for ourselves, for human subjects. Not being able to accurately define an experience isn’t really conducive to trying to identify it in others. We’re trying to find the margins of animal self-awareness without even knowing what those margins look like in the first place, working from a vague outline of what our own look like.

This bias in understanding is also felt in the shape of the methods we use when researching the issue. Humans are very visual creatures, and the mirror test is very visual — the idea of it came to Gallup while he, himself, was shaving and looking into a mirror. But could an animal like a bat, which relies heavily on sound, be able to pass the test in a way that we would perceive it as such, even if it was fully self-aware?

It’s also an assumption that an animal would react differently even if it can perceive the image in the mirror as a reflection of itself. It’s probably a solid assumption, but we don’t really know. We’ve never had the chance to ask a duck, for example, if it would even care in any way that it is seeing its reflection, or bother to react to the realization that there’s a lick of blue paint on its forehead.

None of this is to say that the mirror recognition test is pointless and should be scrapped – quite the contrary. We’ve only come to understand that such questions need to be asked because of all the research performed using this test.

Self-awareness is in many ways something that engineers call a black box. This is a system for which we have a reasonable idea of what goes in (the input) and what comes out (the output), but no idea how the transition from one to the other takes place. Taking a black box apart is of very limited use, as the ‘magic’ inside it relies on how the components work together, something that cannot be fully reflected or recreated by its individual parts.

The way we study black boxes is to make systematic inputs, record the outputs, and then take a really educated stab at guessing what goes on inside. Mirror recognition tests are one of the inputs we used so far to study consciousness and self-awareness, and it has served us well. But we’ve already extracted a wealth of data from it. We should devise new, more sophisticated, more refined inputs tailored for each particular black box to build upon the mirror recognition test.

In the meantime: do animals recognize themselves in the mirror? Some do, yeah. What does that mean for us? Well, it gives us the chance to understand the black boxes that we all have churning around in our heads all our lives by first understanding how tinier, maybe simpler black boxes around us work. And it can even help us see that we’re not so alone on this planet as we may sometimes feel.

This article originally appeared in 2022 and was updated with new information.