Are monkeys self-aware?

New results suggest that rhesus macaques recognize themselves in the mirror, but the debate is far from over

By | September 30, 2010

Rhesus monkeys may recognize their own reflection in a mirror, indicating self-awareness--a trait traditionally reserved for humans, chimpanzees and orangutans and a topic of much debate among researchers, including linkurl:Marc Hauser,; professor of psychology at Harvard University and the recent subject of misconduct investigations.
Rhesus monkey
Image: Wikimedia commons, user 13bobby
The linkurl:results,; published in the September 29th issue of PLoS ONE, question the existence of a stark cognitive divide that separates higher primates from the rest of the animal kingdom. "In most instances, monkeys do not show [self-awareness]," linkurl:Christopher Coe,; director of the Harlow Primate Laboratory at the University of Wisconsin-Madison, who was not involved in the work, said in an email to The Scientist. But the new study "indicates that rhesus monkeys can acquire this ability in the right setting and with the right tools." For years, the Gallup mark test has been the standard method for assessing self-awareness. Researchers dye a small tuff of hair on an animal's head, and then give it access to a mirror. If the animal touched the mark while looking in the mirror, researchers concluded it understood the reflection to be its own. Humans over the age of two, chimpanzees, orangutans and potentially gorillas can conclusively pass this test. Monkeys, on the other hand, nearly always fail. In 1995, Hauser published a controversial linkurl:paper; in Proceedings of the National Academy of Sciences (PNAS), which reported that cotton-top tamarins show signs of self-awareness, despite many failed attempts in the past by other researchers. He used a modified form of the Gallup mark test, however, by dying the entire white head of the tamarin a bright color, such a green or pink. Hauser argued that the small mark was simply not relevant to monkeys, causing them to fail the test in the past. Yet, monkeys react to a Gallup mark that they can see on their arm or hand, noted linkurl:Gordon Gallup,; lead researcher in the field, professor of psychology at the University at Albany, SUNY, and inventor of the Gallup mark test. "If it's salient on their arm, then it ought to be equally salient on their face." Skeptical after reading Hauser's paper, Gallup requested to see some tapes recorded during the study. "When I looked at the tapes, I was absolutely shocked," he said. "There was not a shred of evidence in any of the video tapes that suggested that cotton-top tamarins could recognize themselves in mirrors." In 2001, Hauser reported that he was unable to reproduce the results of the 1995 paper. His new linkurl:findings,;;2-X/abstract published in the American Journal of Primatology, suggested that cotton-top tamarins do not exhibit behaviors suggesting self-awareness, once again limiting this ability in primates to the great apes. Despite the irreproducible results of the 1995 paper, Randy Schekman, editor-in-chief of PNAS, said the journal does not have plans to retract Hauser's original paper. "The Harvard committee investigating Hauser has not contacted us about it, and we have no reason to pursue the matter unless someone challenges the paper." Another linkurl:study,; on the rule learning abilities of cotton-top tamarins, unrelated to his tests of self-awareness, was the subject of the recent misconduct investigation and the retraction of a 2002 Cognition paper. The new study on rhesus macaques now provides more evidence that some monkeys do possess the ability to recognize themselves in mirrors. linkurl:Luis Populin,; a professor of anatomy also at the UW-Madison, who normally studies the effects of drugs such as Ritalin on monkeys, stumbled upon this project when graduate student Abigail Rajala claimed that she observed a monkey using a small mirror provided for enrichment to groom himself. The monkey paid particular attention to the area around an implant in its head, which the researchers used in their studies on attention deficient disorder. The observation prompted Populin and his colleagues to test for self-awareness in the monkeys, replacing the traditional splotch of color used in the Gallup mark test with the head implant. They also used monkeys that had years of experience with mirrors, which Populin believed was a necessary ingredient for them to pass the mark test. While looking into the mirror, the monkeys examined and groomed the area around their implant and other unseen areas on their bodies, such as the genitals. In cases where the implant was removed, the monkeys failed to touch their heads at all, but continued to examine their genitals in the mirror.
This movie shows a monkey waking up from a nap, reaching for the small mirror outside his cage, positioning it to view himself, and grooming the area around the implant while looking at himself. The view of the head implant has been blocked for discretion.
Video courtesy of Luis Populin.
The implanted monkeys also showed sparing amounts of aggressive or submissive social responses, another indication that they did, in fact, see the reflections as themselves. The paper contains a couple of flaws, however, that "render the results inconsequential and uninterpretable," said Gallup. For one, the monkeys can feel the implant in addition to seeing it, unlike the traditional color mark, which controls for tactile cues. Thus, they could be drawn to touch it, despite their reflection in the mirror. However, Populin believes he controlled for this by presenting the monkeys with a mirror blocked by black plastic. When the mirror was concealed, the monkeys failed to examine their implant and their genitals as often. "Subjects may touch the area because it itches or it is irritated," he agreed. "Although if that were the case, one would see no difference between the mirror and no mirror condition." The videos of Populin's work, which were published along with the paper, are no help in solving the debate. Some researchers argue the behaviors in the videos do not illustrate self-awareness, and some argue they do. The videos don't "strike me as compelling, self-directed behavior," said Gallup, "but [they do] strike me as investigative behavior coupled with instances of intermittent social behavior." Contrastingly, linkurl:Charles Snowdon,; professor of psychology and zoology at the UW-Madison, who was not involved in the research, said, "the videos are impressive in that rhesus macaques show some evidence of precursors of mirror recognition," in an email to The Scientist. Whether there exists a blatant cognitive divide separating higher primates from the rest of the animal kingdom still remains open. "For other species, vocal or odor recognition may be more salient," said Coe, "but until paradigms are developed in other modalities we will not know what other species may have [self-awareness]."


Avatar of: anonymous poster

anonymous poster

Posts: 1

September 30, 2010

I always thought the mirror test was a deficient means of testing self-awareness. It seems to test whether or not the animal recognizes itself in a mirror. Nothing more nor nothing less.
Avatar of: Mike Waldrep

Mike Waldrep

Posts: 155

September 30, 2010

Avatar of: Donald Duck

Donald Duck

Posts: 39

September 30, 2010

If we define humans as self aware, what does that mean? After all, when we are sleeping we have no concept of "I", or at least I don't, and many people cannot even "think" verbally or visually right after waking up.\n\nIf we spend so much of our time not aware of ourselves, how do we define a sleeping human as "aware" or "sentient" in a way that distinguishes us from animals?
Avatar of: Evelyn Haskins

Evelyn Haskins

Posts: 5

October 1, 2010

"I always thought the mirror test was a deficient means of testing self-awareness. It seems to test whether or not the animal recognizes itself in a mirror. Nothing more nor nothing less."\n\n\nI agree!! \n\nIf you approach a monkey threateningly it cringes or otherwise reacts -- very much as though it is entirely aware that it is being threatened. (So do dogs! And cats.) That is, im my books, that that that individual is aware that its SELF is being threatened.\n\nWouldn't you call that self awareness? Self "recognition" as in recognising "a reflection of one's self" as "a reflection of one's self" comes only with experience, as any mother who had introduced a baby to a mirror knows!! As for realising that you can actually USE such a reflection to self-groom, that comes much later
Avatar of: David Hill

David Hill

Posts: 41

October 1, 2010

Since humans are old world monkeys, then if humans are "self aware" then at least some monkeys are "self aware." I agree with most commentary here that the mirror test is just that. Just what is "self-awareness" anyway? The question of what constitutes the "self" is a deep philosophical issue, one addressed for thousands of years by some of our greatest thinkers. Scientists should not trivialize the enormous intellectual challenge of this concept by placing too much evidence on simplistic "tests," or by assuming that they can clearly define "self." Perhaps the "self" that you or I think we can understand is the greatest illusion of all.
Avatar of: R CALDWELL


Posts: 6

October 1, 2010

All animals are self aware. It is just some care more than others and just like IQ or EQ, self awareness varies even amongst humans. I have seen some brilliant people with the self awareness of a stick and some absolute morons standing in front of a mirror for hours grooming themselves. I believe it is actually kind of arrogant to dismiss awareness simply because it falls on the low end of a bell curve that is pegged to the human experience and has a humanized litmus test that actually has little to do with awareness. The "mark" needs to be replaced by a sliding scale that measures something other than the learned ability to recognize one's own reflection. I think the previously mentioned "I don't want to be eaten" test works for me.


Posts: 69

October 3, 2010

In late seventies, we were doing unilateral ablation of eyes in macaque monkeys to see changes in the visual cortex biochemically and by rapid Golgi techniques. The place being Hyderabad, we were confronted with an ethical question since the local legend has it that monkeys tend to be self-destructive when wounded surgically or otherwise. Of course, the popular , untested, legend is plain nonsense and we proceeded with the surgeries but carefully observed the monkeys due to our own curiosity. Having done innumerable surgeries of all kinds in rats and mice for experiments, this was also my first chance at seeing the behaviour of a larger animal, but smaller than man, on whom also I had the occasion to operate.\nWell, the monkeys behaved just like us: they treated the wounded area very carefully and did not allow it to come into contact with any external object such as the cage or even own paws and each surgery healed perfectly. Once healing occurred, by which I presume the pain due to touch disappeared, the monkeys became absolutely normal. I wish a kept a mirror in the cage then.\nIs self awareness restricted to a mirror? How about self examination? I presume this awareness is critical for survival at a more primal level.
Avatar of: anonymous poster

anonymous poster

Posts: 1

October 22, 2010

The mirror test to me only indicates that the primate understands the essential concept of what a mirror is. \n\nAt best, it seems to be a "reflection" of self awareness, and perhaps of a learned capacity to perceive the inverted representation of oneself that the mirror produces, and to link it to an internal model of the body in space. It would not surprise me that this could be taught - in so doing have I then taught the monkey to be "self aware"? I think not.
Avatar of: James Reimer

James Reimer

Posts: 2

October 23, 2010

We have a floor length mirror that the dog has walked past often and always ignored his image. However one night he slept in front of the mirror and in the morning, just as it became light enough to see shapes but not details, he started barking at his image because he couldn't recognize himself.\n\nThere have been other times when the dog has been facing the mirror and I have been behind him and silently waved to him. He immediately turned around to look at me.\n\nMaybe some animals just aren't curious or concerned enough about their appearance to respond to a change in it.

Popular Now

  1. Publishers’ Legal Action Advances Against Sci-Hub
  2. How Microbes May Influence Our Behavior
  3. Metabolomics Data Under Scrutiny
    Daily News Metabolomics Data Under Scrutiny

    Out of 25,000 features originally detected by metabolic profiling of E. coli, fewer than 1,000 represent unique metabolites, a study finds.

  4. Sexual Touch Promotes Early Puberty
    Daily News Sexual Touch Promotes Early Puberty

    The brains and bodies of young female rats can be accelerated into puberty by the presence of an older male or by stimulation of the genitals.