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We often try to imagine another person’s state of mind, so that we can
modify our behaviour in the light of it. For instance, we often consider
what other people’s moods are likely to be, the desires they might have,
and we guess the things that they might or might not know. But do other
primates have this ability?

Dorothy Cheney and Robert Seyfarth of the University of Pennsylvania
attempted to test this in the laboratory, with two species of macaque (Animal
Behaviour, vol 40, p 742). There is some evidence that chimpanzees are able
to attribute ‘mental states’ to each other, but for all other primates,
including the macaques, the evidence up until now is anecdotal.

Cheney and Seyfarth placed females in cages from which they could see
a test arena. They put down a plate of appetising food, or sent in a threatening
human ‘predator’, who subsequently hid behind a screen.

In half of these trials, the researchers allowed a female’s offspring
to stay with her so that they could also see what was happening in the arena.
But in the rest of the tests, the offspring saw nothing of what went on.

Cheney and Seyfarth then released the young of all these mothers into
the arena. Half of the infants had prior knowledge of what they would find,
and half of them had no idea.

If the females could attribute mental states to their young, reasoned
the zoologists, then the mothers of the ‘ignorant’ young ought to make more
of a show of alerting their infants, for example, either to the food, with
soft, hooting ‘food calls’, or to the hidden ‘predator’. But Cheney and
Seyfarth found no difference in the behaviour of any of the mothers.

Perhaps the mothers did, indeed, recognise a difference between ignorant
and knowledgeable young, but they just did not act on it. However, Cheney
and Seyfarth believe it is more likely that macaques cannot put themselves
in another’s place, unlike humans. They seem unable to understand that individuals
can differ from themselves, and from other monkeys, in the beliefs that
they have.