We once had a chimp who could sort photographs of apes and human beings into two piles. Apes on one pile, humans on the other. The only trouble was, every time she got to her own picture, she put it on the pile with the human beings.
— Dr. Geoffrey H. Bourne, Yerkes Primate Research Center. Bartlett’s Unfamiliar Quotations by Leonard Levinson, 1971.