Agence France-PresseOctober 17, 2013 11:36
Human yawns are contagious for chimpanzees but, like children, this only happens among apes that have grown beyond infancy, scientists said Thursday.
Playing with a researcher, orphaned young chimps aged between five and eight years began to yawn after their human chum did so, investigators at Sweden's Lund University found.
Infant apes, though, seemed immune to yawn contagion.
Humans behave in a similar way, with contagious yawning starting when they are around four -- about the same age when behaviours emerge that suggest a capacity for empathy.