" Harry Harlow, a well-known American primatologist, was an early critic of the hunger reduction model. He argued that intelligent animals learn mostly through curiosity and free exploration, both of which are likely killed by a narrow fixation on food. He poked fun at the Skinner box, seeing it as a splendid instrument to demonstrate the effectiveness of food rewards but not to study complex behavior. "

― Frans de Waal , Are We Smart Enough to Know How Smart Animals Are?