Some people believe that sharks stupid, robot-like killing machines. However, at least one measure of intelligence, the ratio of brain weight to body weight, suggests that are more intelligent than bony fish, reptiles, amphibians, and even some small mammals. Sharks have relatively big brains--on par with birds and even cats.
Sharks do smart things, too. They have the same five senses as humans, but they also have a sixth “electro-sense”. The sharks’ electro-sense allows them to detect weak electrical signals from their prey before they might otherwise see or hear them.
Sharks can also sense changes in their electric fields in relation to the earth’s magnetic field. This helps them navigate during long migrations in a featureless ocean in which humans would be completely lost without a compass.
Since the 1950’s there have been several experiments that indicate sharks smart enough to learn, to remember, and to change behavior based on learning.
(maybe we can find some more specifics on the intelligence studies).
Clark, E. 1959. Instrumental conditioning in lemon sharks. Science 130 (3369): 217-218.
Clark, E. 1978. Sharks that ring bells. pp. 109-124. In: V. & R. Taylor & P. Goadby (ed.) Great Shark Stories, Harper & Row Publishers, New York
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