August 18, 2006 Dolphins, mammals long famous for their intelligence, might not be so smart after all. Paul Manger, a biologist at Johannesburg’s University of the Witwatersrand, says that despite the large brains found in dolphins, size does not indicate intelligence. Instead, their large brain size is the result of a warm-blooded animal living in a cold-water environment.

Dr. Manger’s study, published in the May 2006 issue of the Cambridge Philosophical Society’s Biological Reviews, deals specifically with brain structure in cetaceans, the order of mammals that includes dolphins, whales, and porpoises. Manger argues that much of dolphins’ reputation as being exceptionally wise derives from unquestioned assumptions that intelligence correlates with brain size.

As scientists attributed human intelligence to our large brain size, they also posited cetaceans’ large brains (some are heavier than eight kilograms) as proof that sufficient matter is needed to produce complex thought. On the other hand, Manger’s study finds that cetacean brains have an unusually high number of glial cells, which provide insulation for brain functioning and account for a large amount of the brain’s mass.

Furthermore, Manger argues that many of the supposed talents of dolphins are actually the products of “compulsively anthropomorphic” anecdotes. Previous studies have suggested, for example, that dolphins are the only “alien” species with which humans might have meaningful conversations. Other scientists have attempted to decipher “dolphinese,” or teach human speech to dolphins.

Manger asserts that all attempts to teach a human language to dolphins have been based on stimulus-response mechanisms, which are regarded as somewhat unsophisticated. According to Manger’s survey of previous cetacean research, studies have shown dolphin repertoires to have approximately seven different sounds, and that these vocalizations are species-specific calls.

Invasive experiments of cetacean brains are impossible, due to the restrictions of the Marine Mammal Protection Act; therefore, the only means of studying brain function is through comparison of laboratory experiments and post-mortem tissue.

Manger’s study is likely to provoke defenses of dolphin speech and intelligence, but Flipper’s crime-fighting reputation may never recover.

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