The most prolific and sophisticated of the animal artists are primates. Of course, we're familiar with the work of human artists, but other apes are also apt at expressing themselves abstractly. The sign language-speaking gorilla, Koko, is famous for her sensitive artwork, as is her male companion, Michael. Chimpanzees like Congo, who have been raised by people, often grow up with an affinity for playing with crayons just as human children do.