"Two chimps had been shut out of their shelter by mistake during a cold rain storm. They were standing dejeted, water streaming down their shivering bodies, when Professor Köhler chanced to pass." Upon opening the door for the two chimps, Dr. James Leuba recounts, "instead of scampering in without more ado, as many a child would have done, each of them delayed entering the warm shelter long enough to throw its arms around his benefactor in a frenzy of satisfaction."
"Chimpanzees," primatologist Frans de Waal points out, "do not normally hug their caretakers for no reason." It's a compelling…