Besides humans, which animals are the most intelligent?

According to Edward O. Wilson, a behavioral biologist (scientist who studies the behavior of animals), the ten most intelligent animals are the following:

1. Chimpanzee (two species)
2. Gorilla
3. Orangutan
4. Baboon (seven species, including drill and mandrill)
5. Gibbon (seven species)
6. Monkey (many species, especially the macaques, the patas, and the Celebes black ape)
7. Smaller-toothed whale (several species, especially killer whale)
8. Dolphin (many of the approximately eighty species)
9. Elephant (two species)
10. Pig

Source: Wallace, Irving. The Book of Lists #2, p. 104.

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