Attending to behaviour versus attending to knowledge: examining monkeys' attribution of mental states

The ability of monkeys to attribute mental states such as ignorance to each other was examined in two experiments using four captive groups of Japanese and rhesus macaques, Macacafuscata and M. mulatta. In the first experiment, females were shown food or a predator, either in the presence of their offspring or alone, to determine whether they would attempt to alert ignorant offspring more than knowledgeable ones. The behaviour of mothers appeared to be unaffected by the knowledge of their offspring. In the second experiment, a juvenile offspring of a dominant female was isolated in an enclosure with a normally subordinate adult female while the juvenile's mother sat nearby behind either a glass barrier, an opaque barrier or a one-way mirror. In the mirror condition, the two subjects could see the mother, but she could not see them. The behaviour of subjects under the mirror condition was intermediate between that under the glass and opaque conditions. Subjects were probably sensitive to the mother's orientation and attentiveness, but there was no evidence that they recognized the difference between their own visual perspective and that of the mother. Monkeys and apes are clearly adept at recognizing the similarities and differences between their own and other individuals' social relationships. What is not known is whether they are equally adept at recognizing the similarities and differences between their own and other individuals' states of mind (e.g. discussions by Premack & Woodruff 1978; Cheney & Seyfarth 1990; Whiten, in press). For example, in many species of monkeys and apes, subordinate males will only attempt to copulate after they have manoeuvred their partners into a position out of sight of more dominant males (for many similar anecdotes see de Waa11982, 1989; Byrne & Whiten 1988). But what is the basis of this apparent deception? Does a subordinate male copulate behind a bush because he knows that he can influence what the dominant male sees and therefore knows? Or does the subordinate male go behind a bush simply because he has learned from past experience that he can avoid attack whenever he copulates out of sight of the dominant male? There is very little evidence that monkeys ever act to alter the beliefs of other animals, rather than their behaviour. We have no evidence that 'deception' is not simply the result of acutely observed behavioural contingencies derived from past experience: if I do X, he will do Y. A consideration of alarm calls reveals similarly incomplete evidence for an ability to attribute mental states to others. Alarm calls in many species of birds and mammals are not obligatory but depend on social context. Individuals often fail to give alarm calls when there is no functional advantage to be gained by alerting others; for example, when they are alone or in the presence of unrelated animals (e.g. roosters, Gallus gallus: Gyger et al. 1986; ground Squirrels, Spermophilus beldingi: Sherman 1977; vervet monkeys, Cercopithecus aethiops: Cheney & Seyfarth 1985). In all studies to date, however, signallers call regardless of whether or not their audience is already aware of danger. Vervet monkeys, for example, will continue to give alarm calls long after everyone in the group has seen the predator (Cheney & Seyfarth 1981, 1985). There is no evidence that animals recognize that other individuals can possess knowledge different from their own, or that they selectively inform ignorant individuals more than knowledgeable ones. Like alarm calls, food calls can function to inform others of relevant features of the environment. Even among chimpanzees, Pan troglodytes, however, there is no evidence that signallers take into account their audience's state of mind when giving calls. Chimpanzees' loud calls appear to convey precise information about the presence and abundance of food. However, calling rate seems to be influenced primarily by the relative abundance of the resource (Wrangham 1977; see also Hauser & 0003-3472/90/100742+12 $03.00/0 9 1990 The Association for the Study of Animal Behaviour