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Throughout history, intelligence has often been considered a quality unique to humans.
Influential thinkers, such as Rene Descartes, had even argued that unlike people, animals were simply mindless creatures incapable of any complex thought.
But several recent studies have challenged this long-held view.
Crows, for instance, invent tools. In experiments, the clever birds were observed using twigs and wires to snatch food from hard-to-reach places.
A similar brand of ingenuity is displayed by octopuses, which use rocks to build homes in crevices along the ocean floor. The eight-legged eggheads also have a reputation for mischief, as one researcher learned when he captured one on video sneaking out in the middle of the night to feast on nearby fish, then returning to its tank as if nothing had ever happened.
A few species, however, deserve special mention for being at the head of the class.
Chimpanzees and Bonobos
Chimpanzees and bonobos have DNA that is 98 percent identical to ours, and the similarities don't end there. They hunt in groups, invent tools and transfer learned behaviors to others.
This tendency to share knowledge within a group has led some researchers to suspect that the primates may also possess a capacity for language. In the '60s, a chimp named Washoe surprised many scientists when she began to acquire sign language. Before her death last year, it is believed that she learned to use about 250 signs.
Kanzi is another ape that has shown a prodigious knack for gab. The 27-year-old bonobo picked up language as an infant by watching scientists attempt unsuccessfully to teach his mother to communicate through keyboard symbols.
Within a short time, Kanzi learned thousands of words. Smithsonian magazine reported that during an outing in the forest, Kanzi used the keyboard to ask researchers for matches and marshmallows. With the items in hand, he prepared a campfire and toasted the marshmallows on a stick.
African Gray Parrots
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