Los Angeles, Feb. 14 -- Cognitive biologists and primatologists have documented playful teasing in four species of great apes.

Babies playfully tease each other as early as eight months of age. Because language is not required for this activity, nonhuman animals may exhibit similar forms of playful teasing.

Ape teasing, like human joking behaviour, is provocative, persistent, and combines aspects of surprise and play. Because all four great ape species engaged in playful teasing, it is likely that the prerequisites for humor evolved in the human lineage at least 13 million years ago.

Joking is an important part of human interaction that draws on social intelligence, an ability to anticipate future actions, and an ability to recognize a...