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The answer may be politics, which is hardly confined to human society. Scottish psychologists Richard Byrne and Andrew Whiten believe chimps are positively "Machiavellian" in their efforts to acquire power within a group. In the Mahale Mountains in Tanzania, for instance, Japanese primatologist Toshisada Nishida observed one male chimp shift his support between two more dominant males who needed his allegiance to maintain power. The bigger males curried favor with this artful manipulator by allowing him access to fertile females. When a ruler began to take him for granted, the canny old chimp would shift allegiance to the pretender, thus ensuring himself continual access to mates without fear of attack from his superiors.
In the complex game of social chess played by chimps and other primates, having the intellectual skills to anticipate a rival's moves and engage in deceit is a distinct advantage. Consider the double deception observed at a feeding station in Tanzania's Gombe Stream Reserve. A wild chimp had the luck to be alone next to a feeding box when it was opened by remote control. Noticing that another, more dominant chimp was approaching, the first one closed the box and moved nonchalantly away until the second chimp moved on. Once the interloper was gone, the first chimp opened the box to claim the food. The second chimp, however, had cleverly hidden himself just out of sight and triumphantly returned to snatch the bananas. There are enough examples of such ape trickery to suggest that perhaps Koko really was lying when she made the signs "Kate there bad."
Knowing Whom to Trust
A crucial question raised by such devious behavior is, To what degree does an animal actually understand what's in its rival's mind? If an animal knows when another creature is misinformed or has valuable knowledge, it gains an enormous advantage. In the late 1980s, a pioneer of animal-language work came up with an ingenious way of probing this question.
David Premack actually devised his simple test to study children. First, a child is shown a tableau in which a little girl named Sally puts a marble in her bag and then leaves the room. Before Sally returns, another girl, Ann, takes the marble from Sally's bag and puts it in a box. The child is then asked where Sally will look for the marble when she returns. Three-year-olds will point to the box, because that is where the marble is; but four-year-olds understand that Sally has the mistaken belief that the marble is still in her bag and that she will look for it there.
Psychologist Daniel Povinelli at the University of Southwestern Louisiana has conducted a number of experiments that adapt Premack's test for primates. In one version, chimpanzees had to choose which of two humans would be better at helping them find some hidden food. While the animals themselves could not see where the food was being hidden, they could observe that only one of the two humans had a full view of the process. When asked to choose a helper, the chimps overwhelmingly chose the human who knew where the food was hidden.
Just as four-year-olds have an insight that three-year-olds lack, chimps have an advantage over lesser primates. When Povinelli tried his experiment with rhesus macaques, the monkeys proved unable to distinguish between the human who knew where the food was and the one who didn't -- even after 600 attempts.