Whether we're assessing our physiques or checking for food stuck in our teeth, most of us consult a mirror regularly to make sure we appear the way we expect. Though it may seem an unremarkable feat, the ability to recognize oneself in the mirror is actually exceptionally rare among animals. Indeed, only humans and their closest kin, the great apes, have shown this capacity, suggesting that factors specific to great apes and humans drove its evolution. Findings announced today in the early online edition of the Proceedings of the National Academy of Sciences, however, indicate that we and our primate relatives are not alone. According to the report, dolphins, too, exhibit mirror self-recognition.

To test for dolphin self-awareness, Diana Reiss of Columbia University and Lori Marino of Emory University exposed two bottlenose dolphins to reflective surfaces after marking the dolphins with black ink, applying a water-filled marker (sham-marking) or not marking them at all. The team predicted that if the dolphinswhich had prior experience with mirrorsrecognized their reflections, they would not show social responses; they would spend more time in front of the mirror when marked; and they would make their way over to the mirror more quickly to inspect themselves when marked or sham-marked. The experiments bore out all three predictions in both dolphin subjects. Moreover, the animals even selected the best reflective surface available to view their markings.

Intriguingly, whereas chimpanzees take interest in marks on fellow chimps in addition to marks on their own bodies, the dolphins focused on themselves. "Dolphins may pay less attention to marks on the bodies of companions because, unlike primates, they do not groom each other," the researchers write. "This difference makes our findings even more interesting because dolphins clearly are interested in marks on their own body despite the fact that they do not have a natural tendency toward social grooming."

The extent of dolphin self-awareness remains to be explored. But the fact that they have passed the mirror test means that self-recognition may result from large brains and advanced cognitive ability, as opposed to being a by-product of primate-specific factors. That dolphins and primateswhich differ profoundly in their brain organization and their evolutionary historiesshould both exhibit this unusual ability, the authors note, represents "a striking case of cognitive convergence"