Dolphins Recognize, Admire Themselves in Mirrors, Study Finds

Betsy Querna
National Geographic Today
May 2, 2001
Dolphins recognize themselves in mirrors—one of the few mammals
other than humans that have the ability to do so, according to a new
study published this week.

Described in the May issue of the Proceedings of the National Academy of Sciences, the study found that dolphins not only can recognize themselves in a mirror but also can notice changes in their appearance.

Prior to this research, only higher primates, such humans and chimpanzees, had demonstrated self-recognition in mirrors.

Diana Reiss of the Osborn Laboratory of Marine Sciences at the New York Aquarium and Lori Marino of Emory University in Atlanta conducted the study involving two bottlenose dolphins from the New York Aquarium.

The scientists first marked the dolphins with "sham" marks, then exposed them to a mirror. After several repetitions, the scientists put temporary black ink on parts of the dolphins' bodies, which the animals could see only in a mirror. In each of the trials, the dolphins went to the mirror to examine the areas the scientists had marked.

Marino and Reiss said their findings "provide definitive evidence that the two dolphins in this study used the mirror…to investigate the parts of their body that were marked."

Brain Links Unknown

The mark test was devised by Gordon Gallup, Jr., a professor of psychology at the State University of New York in Albany. He used the test to demonstrate self-recognition by chimpanzees. While the test has been used with many other animals, including primates, elephants, and parrots, this is the first time non-primates have reacted to a mirror by using it to examine themselves.

One of the most important implications of this study is that it shows that the ability to recognize one's own appearance is not specific to primates. According to Marino, the study is interesting because dolphins and primate brains have evolved along very different lines. "Our study shows that the same behavior can be an outcome of two very differently organized brains," she said.

Previous research suggested that self-recognition was possible only in animals with a frontal lobe, such as humans and other primates. This study, however, suggests that the ability is probably linked with more general characteristics, such as large brain size and cognitive ability.

An interesting difference between primates' and dolphins' behavior is that the dolphins paid attention to the markings on their own bodies but not to similar markings on other dolphins. Similar research on chimpanzees has shown that they notice markings on their peers. The scientists speculate that the difference may be related to the fact that chimps groom each other but dolphins do not.

Ethical Questions

The study also raises questions about the self-awareness of dolphins and the ethics of using these animals in scientific experiments. The topic of animal consciousness is controversial, and this kind of research strengthens many scientists' conviction that dolphins have an acute sense of themselves and others.

Complete results of the study will be published in the May issue of the Proceedings of the National Academy of Sciences and online at

This story was aired on the television news show National Geographic Today on May 1 and 2.

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