Monkeys Recognize Faces (Hence the Incident in Zimbabwe, Where a Monkey Peed on the President?)

A visual illusion has provided clues about how monkeys recognise faces. In a study, rhesus monkeys responded to the "Thatcher effect", a strange phenomenon that makes it difficult to detect changes in an upside down face. The study, in the journal Current Biology, is the first to show this effect in non-human animals. The authors say this suggests that the ability to identify a familiar face may have evolved in an ancestor common to humans and rhesus monkeys.

link: BBC NEWS | Science & Environment | Monkeys fall for visual illusion