A group-specific arbitrary tradition in chimpanzees. Monkeys Can Think about Thinking, Too. Evidence of non-human primates whispering. Planning of the Apes: Zoo Chimp Plots Rock Attacks. Think people are the only ones who can plan for the future?
You may change your mind when you hear the story of Santino the chimpanzee, whose premeditated attacks on zoo visitors are described today in Current Biology. When Santino was first transferred to Sweden's Furuvik Zoo in 1983 at the age of five, he was relatively calm and passive, lead study author Mathias Osvath, a postdoctoral student in cognitive sciences at Lund University in Sweden, tells ScientificAmerican.com. But by the time the primate reached sexual maturity at age 17, he had become so aggressive that he killed the only other male chimp at the zoo. (Oddly, Santino had saved the life of his comrade just five years earlier by untangling a play rope that had wrapped around his neck.) It was shortly after this fatal attack that zookeepers began to notice that Santino had developed a habit of throwing stones at zoo visitors, who were safely situated behind a five-foot- (1.5-meter-) high fence.
Self-Recognition in Apes. I Spy a Cat in a Tree. Peanut Trick.