For the first time, monkeys recognize themselves in the mirror, indicating self-awareness (w/ Video)

September 29, 2010
In the lab of Luis Populin, University of Wisconsin-Madison professor of anatomy, a rhesus macaque monkey stares at himself in a mirror, as the first demonstration that any monkey has a degree of self-awareness. Photo: courtesy Luis Populin

Typically, monkeys don't know what to make of a mirror. They may ignore it or interpret their reflection as another, invading monkey, but they don't recognize the reflection as their own image. Chimpanzees and people pass this "mark" test — they obviously recognize their own reflection and make funny faces, look at a temporary mark that the scientists have placed on their face or wonder how they got so old and grey.

For 40 years, scientists have concluded from this type of behavior that a few species are self-aware — they recognize the boundaries between themselves and the physical world.

Because , our closest relatives, pass the test, while almost all other primate species fail it, scientists began to discuss a "cognitive divide" between the highest and the rest.

But a study published today (Sept. 29) by Luis Populin, a professor of anatomy at the University of Wisconsin-Madison, shows that under specific conditions, a rhesus macaque monkey that normally would fail the mark test can still recognize itself in the and perform actions that scientists would expect from animals that are self-aware.

The finding casts doubt on both the relevance of the mark test and on the existence of a definitive cognitive divide between higher and lower primates.

In the lab of Luis Populin, University of Wisconsin-Madison professor of anatomy, a rhesus macaque monkey examines himself in a mirror, as the first demonstration that any monkey has a degree of self-awareness. Video: courtesy Luis Populin

Populin, who studies the of perception and behavior, had placed head implants on two rhesus macaque monkeys, while preparing to study attention deficit disorder. Then Abigail Rajala, an experienced animal technician who is in the university's Neuroscience Training Program, mentioned that one of the monkeys could recognize himself in a small mirror. "I told her the scientific literature says they can't do this," says Populin, "so we decided to do a simple study."

Much to his delight, it turned out that the graduate student was right.

In the standard mark test, a harmless mark is put on the animal's face, where it can only be seen in a mirror. If the animal stares at the mirror and touches the mark, it is said to be self-aware: It knows that the mirror shows its own , not that of another animal. (Animals that lack self-awareness may, for example, search for the "invading" animal behind the mirror.)

Rhesus macaques, a mainstay of medical and psychological research, have long failed the mark test.

But in Populin's lab, the monkeys that got the implants were clearly looking in the mirror while examining and grooming their foreheads, near the implant. Tellingly, they were also examining areas on their body, particularly the genitals, that they had never seen before. In some cases, the monkeys even turned themselves upside down during these examinations. In other cases, they grasped and adjusted the mirror to get a better view of themselves.

When the researchers covered the mirror glass with black plastic, these behaviors disappeared, and the monkeys ignored what had been a subject of fascination.

Furthermore, although a macaque will often interpret its reflection as representing an intruding monkey and adopt either an aggressive or submissive response, the implanted monkeys showed dramatically fewer of those "social" behaviors compared to the behaviors, such as exploring hidden body parts, that indicate self-awareness, Populin says.

"This report makes a unique contribution to our views about primate self-awareness because the 'mirror test' has been the traditional gold standard for determining if a person and/or animal met a criterion for having a sense of self," says Christopher Coe, a primatologist and professor of psychology at UW-Madison. "If a young child, brain-damaged adult or animal was able to recognize and appreciate that the image in the reflection was really them, then it was interpreted as proof of being aware."

Thus, Coe says, "If we follow that logic through with the belief that mirror recognition is proof of a sense of self, then we need to extend that attribute at least to rhesus monkeys."

Scientists who have used the mark test to explore self-awareness have found the quality in one species of bird, in one individual elephant, and in dolphins and orangutans. And so instead of asking how self-awareness evolved only among primates, they face the larger question of how it evolved multiple times in distantly related species.

The study may refine how the mark test is used, Populin says. "We clearly have data showing that these animals recognize themselves in the mirror, but fail the mark test."

The mounting data on self-awareness has undermined the concept of a cognitive divide in the primate lineage, Populin says. "There is another idea in primatology, and Charles Snowdon of UW-Madison has contributed to this, that instead of a divide, self-awareness has evolved along a continuum, so we will find it in different forms in different locations on the tree of evolution. I think the mark test may not be sensitive enough to detect self-awareness in the lower species; they may have it, but in a different form, and it may show up in different situations, using different tests."

Explore further: Pigs learn to understand mirrors

More information: The study, with several videos of the monkeys, appears in today's PLoS One, at

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5 / 5 (1) Sep 29, 2010
I would agree on the fact that the scientific standard is what should be evaluated. My dog knows that the mirror is a reflection of herself, as well as myself. She obeys hand signals from me from looking at the glare in the glass, she looks at herself a lot as well. She knows it is her/me in the reflection.
5 / 5 (1) Sep 29, 2010
Dolphins easily pass this test. Why hasn't their intelligence received greater attention? I believe dolphins should be protected because they're obviously extremely intelligent and self-aware.
4 / 5 (1) Sep 29, 2010
my cat has always attacked any other cat that she had came in contact with but she did not attack her image in the mirror. So we can add cats to animals with self awareness. and hopefully one day we will devise a test that will conclusively show that ants are self-aware. The real question for me is at what level of complexity of the brain do we start seeing similar cognitive facts. Dogs are known to feel jealousy and cats do too. So we can simply conclude that jealousy is not a human characteristic because it's out there.
5 / 5 (1) Sep 29, 2010
That an explanation for the recurrent evolution of varying degrees of self-awareness is needed is a fascinating proposition.

I wish the reviewer had mentioned the authors' hypothesis that it was the presence of the implant which caused this previously unobserved behavior by macaques. I wonder if FMRI could help pin down why the implants cause this changed behavior.

Regarding epsi's cat attacks, it may be the lack of aggressive behavior by the image along with lack of smell plus other "other-catness" factors which escape a human's immediate observation that result in the lack of attack against a mirror image, although my cats have always managed to figure out how to demonstrate to me how important their needs were, so I'm not dismissing what espi reports.
1 / 5 (1) Sep 30, 2010
Dont know about cats as i can remember 2 ammusing instances.

1. I paused a program that wasshowing a kitten about to pounce towards the camera as i needed a drink when i came back my cat was in a very rigid pose watching the kitten. when i unpaused and it pounced my cat sort of "flew" as only a cat can and hid behind a couch.

2. i had a new food tray with a tigers face on it that when i was carrying with face fowards caused both my cats to freak out and hide.

So sadly i say its unlikely that cats are self aware.
3 / 5 (2) Sep 30, 2010
Water is the natural mirror, but in nature water is always horizontal yet humans always mount mirrors vertically for the mirror test ~ when will someone try laying the mirror horizontally, just like they are in nature??
1 / 5 (1) Sep 30, 2010
I wonder actually how smart animals understand the world, another test which can be done is to record the animal doing something, then to play this to the animal, will it get this is "me" from the past?
1 / 5 (1) Sep 30, 2010
Because chimps, our closest relatives, pass the test, while almost all other primate species fail it
Uhm, no they don't. All Hominidae pass the test. This abstract is interesting because it appears that all catarrhines may understand the test, however it appears the homonid that wrote the abstract doesn't understand phylogeny.
2 / 5 (4) Oct 01, 2010
Because chimps, our closest relatives, pass the test, while almost all other primate species fail it, scientists began to discuss a "cognitive divide" between the highest primates and the rest.
If this divide really existed, then at some point a child should cross it. This should show as a discontinuity in her psychological development.

The mirror test was devised to prove us different from "animals". Too bad that even "fish" pass it. It may well be that it soon gets rejected as having anything to do with self awareness. No woman can pass a mirror without checking their image while men walk through a hall of mirrors without even once looking at their image. Does that mean that men aren't self aware? (Don't ask the feminists.)
not rated yet Oct 01, 2010
You're not understanding the test.

The test asks whether you can identify yourself, fish don't do that, they recognize a fish, but not that it is merely a reflection of themself.

Children don't develop this ability until after age 2 (I think, might be a little earlier).

The way the test is done is by putting a spot on the face of the individual. If the individual reaches for the mirror, they fail. If they reach up and touch their face where the spot is, they pass.
not rated yet Oct 03, 2010
I've raised a lot of birds. Cockatiels recognize themselves in the mirror but buggies don't. Pigeons don't either. Pigeons (the smarter individuals) run around to peep behind the mirror. Its quite amusing. Budgies behave as if its another budgie in the mirror. One of my male budgies used to masturbate looking in the mirror!
1 / 5 (1) Oct 03, 2010
There is variation in individuals as well. I've managed to get the odd dog to recognize themselves in a mirror, and some not. Some breeds of dogs are well known for being able (higher occurrence) to recognize themselves in a mirror. Dalmatians being one.

It's almost as if one is then creating the egoic function in the given critter or being, starting from the moment(s) of recognition. ie the understanding of the reflection existing, at all.

Self awareness. How much you gots? and are you doing anything useful with it?

Just for the sake of the reasonable dig, The rightwing nutbars ---I'd hazard a guess that they are the slowest to come to terms with the idea of a reflection in a mirror, as maturing children go.
1 / 5 (1) Oct 03, 2010
Budgie to masturbate! I just wonder how this is posible morphologically(I guess this is one really inventive budgie ).... just give to the poor parrot female.

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