thought these subjects didn’t have this ability. The indications are that if you fail the mark test, you’re not self-aware. This opens up a whole field of possibilities,” Populin said.

Populin doesn’t usually study monkey self-awareness. The macaques described in this study, published September 29 in Public Library of Science , were originally part of his work on attention deficit disorder. But during that experiment, study co-author Abigail Rajala noticed the monkeys using mirrors to study themselves.

So-called mirror self-recognition is thought to indicate self-awareness, which is required to understand selfhood in others, and ultimately to be empathic. Researchers measure this with the “mark test.” They paint or ink a mark on unconscious animals, then see if they use mirrors to discover the marks.

It was once thought that only humans could pass the mark test. Then chimpanzees did, followed by dolphins and elephants. These successes challenged the notions that humans were alone on one side of a cognitive divide. Many researchers think the notion of a divide is itself mistaken. Instead, they propose a gradual spectrum of cognitive powers, a spectrum crudely measured by mirrors.

Indeed, macaques — including those in Populin’s study — have repeatedly failed the mark test. But after Rajala called attention to their strange behaviors, the resarchers paid closer attention. The highly social monkeys only rarely tried to interact with the reflections. They used mirrors to study otherwise-hidden parts of their bodies, such as their genitals and the implants in their heads. Mark tests not withstanding, they seemed quite self-aware.

“I think that these findings show that self-awareness is not an all-or-nothing phenomenon,” said Lori Marino, an Emory University evolutionary neurobiologist who was not involved in the study. “There may be much more of a continuum in self-awareness than we thought before,”

According to Emory University primatologist Frans de Waal, the new findings fit with his work on capuchin monkeys who don’t quite recognize themselves in mirrors, but don’t treat the reflections as belonging to strangers. “As a result, we proposed a gradual scale of self awareness. The piece of intriguing information presented here may support this view,” he said.

However, de Waal cautioned that “many scientists would want more tests and more controls” — a warning especially salient in light of a high-profile controversy involving Marc Hauser, a Harvard University evolutionary biologist who appears to have overstated the cognitive powers of his own monkeys.

“What you’re seeing in the videos is subject to all kinds of interpretations,” said Gordon Gallup, a State University of New York at Albany psychologist who invented the mirror test, and has administered it with negative results to rhesus monkeys. “I don’t think these findings in any way demonstrate that rhesus monkeys are capable of recognizing themselves in mirrors.”

Populin said his monkeys may have developed an unusual familiarity with mirrors, which are given to them as toys during infancy. The presence of saltshaker-sized implants screwed into their skulls may also have captured their interest more readily than an inked mark.

Marino, who helped demonstrate self-recognition in bottlenose dolphins, disagreed. “The videos are absolutely convincing,” she said. “I have been trying to find an alternative explanation for the results – and haven’t come up with one yet.”

Marino said the findings fit with other research on monkey cognition, including a since-replicated Journal of Experimental Psychology study in which macaques displayed unexpectedly sophisticated math skills and passed other, non-mirror-based tests of self-awareness.

“There are many ways to look at animals. Mirror tests are not the end-all and be-all,” said Diana Reiss, a mammal cognition specialist at the City University of New York.

If research continues to find that monkeys possess higher-than-expected awareness, it could influence how researchers and the public think about biomedical research on monkeys. Macaques were critical in the development of a polio vaccine during the 20th century and, more recently, the refinement of embryonic stem cell techniques.

“I would absolutely hope that we do not stop using them now. Their contributions have been immense,” said Populin, who studies how ritalin affects the brain’s prefrontal cortex.

“There are decisions I would make with a monkey, that I would not feel comfortable making with a chimpanzee,” said University of Wisconsin psychologist Chris Coe, who was not involved in the study. “Some of the other cognitive abilities that monkeys would have to show, I don’t believe they do. I don’t believe they sit and ponder their fate, or reflect on the past, or fret about the future, because they are able to see themselves in a mirror,” he said.

But Coe said the findings underscore the importance of providing macaques with better care. He believes they do influence the equations by which society must continually balance the harms and benefits of research. “A study such as this one, that pushes our own awareness of what monkeys can and can’t do, challenges us,” Coe said.

A more accurate understanding of animal awareness may ultimately require better tools, said Marino. Like every researcher but Gallup, she was skeptical of the mirror test, which she said “is shaped more by the cognitive limitations of human researchers than anything else.”

Wrote Marino in an email, “Other animals may be more deeply contemplative than humans – we just don’t know.  That’s really the bottom line. Any scientist who tells you they know that other animals don’t think as richly or as complexly as humans – is, well, not being scientific.”

Image & Videos: 1) Rhesus macaques. Paul Asman and Jill Lenoble, Flickr. 2) Rhesus macaque using a mirror to inspect parts of himself that cannot typically be seen./University of Wisconsin. 3) Rhesus macaque using a mirror to study the implant in his head./University of Wisconsin.

See Also:

• Chimps: Not Human, But Are They People?
• Free-Range Research Could Save Chimps — and Our Conscience
• A Different Take on Great Ape Personhood
• Video: Chimpanzees Mourn Their Dead
• Whales Might Be as Much Like People as Apes Are
• Sperm Whale Voices Are Personal

Citation: “Rhesus monkeys (Macaca mulatta) do recognize themselves in the mirror: implications for the evolution of self-recognition.” By Abigail Z. Rajala, Katharine R. Reininger, Kimberly M. Lancaster, Luis C. Populin. Public Library of Science One, September 29, 2010.

Brandon Keim’s Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on an ecological tipping point project.

Authors: Brandon Keim

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