Historical artwork of four great apes. These four apes are catarrhines, an infraorder which includes the apes and Old World monkeys. Apes, unlike monkeys, do not have tails, are more intelligent and depend more on their eyes than their noses. The great apes seen here are (from bottom left working clockwise) an orangutan, a chimpanzee, a gorilla and a human. There is some debate as to whether humans should be considered great apes, though a chimpanzee shares more genetic material with a human - about 99% - than with a gorilla. Illustration by Ernst Haeckel, first published in his Anthropogenie (1874).