(Original Caption) Koko, now 3-1/2, has learned 120 sign language signals. Miss Patterson, a Stanford student working on her PH.D., chose sing language for Koko because primates, other than man, lack vocal apparatus with enough flexibility for verbal language. Here Koko asks for an orange from Penny by extending her left arm away from her body (l). At (r), Koko gives the orange sign with her right hand, using a clockwise rotation of clenched fist pressed to her lips.
