Cajoling bored friends to keep playing with you is not limited to humans. A gorilla that wants to continue a game will also try to do this, and will even deliberately lose if necessary. This hints that gorillas may have "theory of mind" - the capacity to attribute mental states to others.



Richard Byrne and Joanne Tanner of St Andrews University in the UK videoed gorillas at San Francisco Zoo. As well as engaging with a toy and another gorilla, the animals seemed aware of how their playmate was interacting with the toy. "The gorillas could encourage their playmates when they were losing interest, or self-handicap if there was a danger of winning the game," says Byrne.

This is the first time animals have been observed following a playmate's interaction with a third object - a skill picked up by humans at 9 months old. If you thought your pet dog does this, you're wrong. With dogs, cats, lions and bears "the animal wants to win the game, rather than keep it going", Byrne says. "This is different to throwing a stick for your pet dog."

Gorilla's eye view

Because the gorillas seem to be taking account of the thoughts of others, they are showing some theory of mind competence, says Byrne, although they do not pass a theory-of-mind test called the false belief test, which looks at the ability to infer another's perspective.

In the false belief test, two individuals are shown playing with a toy, before placing it in a box. After one of them leaves the room, the other person moves the toy and places it in a bag. When the first person returns to the room, where will they look for the toy? Those with theory of mind - the ability to infer another's perspective - will know that the first person will look in the box. Children younger than 4 or 5 have yet to develop theory of mind and think the person will look in the bag. Similar false belief tests that don't require language can be set up for animals.

Theory of mind?

Felix Warneken at Harvard University agrees the study provides "promising evidence" for collaborative behaviour in gorillas. However, Josep Call, at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, says he has seen this behaviour in chimpanzees before.

Iona Stewart at ZSL London Zoo, who has been looking after captive gorillas for 13 years, says there is "no question" that gorillas have theory of mind. "Anyone who spends time with gorillas will have known this for years," she says. "Not a day goes by when you don't see some example of this sort of behaviour."

The typical gorilla sense of humour, Stewart says, is Schadenfreude. One gorilla she knew would poke a stick at strangers then look the other way. "If they could whistle, they'd be whistling, but they're not quite clever enough to get away with it."

Journal reference: Animal Cognition, DOI: link