Chimpanzees appear to know what’s on their friends’ minds

The other day the Northerner and I were walking home from the tube and I shouted out as I thought he was about to cross the road into the path of an on-coming bus turning the corner. As it happens the bus stopped on the bend because the lights were red. But my “alarm” call was genuine because I honestly thought he hadn’t seen it. He had of course, and all I’d managed to do was to deafened his eardrum and look like a pratt.

Humans are not the only species of primate that send out warning signals to each other. How monkeys and apes communicate vocally has long be a source of fascination among scientists. The “Theory of Mind” has produced a number of different results from various tests over the years. Some primates appear to demonstrate having an insight into the minds of others from what those individuals can see, although they may not understand that they know this; in others “perception” can lead to knowledge. Without a conversation with our nearest kin we may never know exactly what their calls mean so for the time being vocalisation studies continue.

Chimpanzees moving through the forest will often walk on all fours. Being at ground level however poses a number of different threats, not least from venomous snakes. The ability to recognise others’ knowledge and beliefs is something that is quite unique in humans and is key to human cognition.

In a study carried out in the Budongo Forest Reserve in Uganda, researchers tested whether chimpanzees would raise an alarm call if they thought group members who were lagging behind were ignorant of a potential threat that lay ahead of them that they hadn’t seen.

Chimps are known to scream or bark when there is a serious threat like a potential ambush from a large predator like a leopard or indeed a rival chimp troop. But they are less likely to make this sound if the threat less serious. Snakes do not prey on chimps but they are poisonous and will bite if trodden on.

 

The researches placed a model viper lying camouflaged on the pathway and tested 33 apes to see their reaction. The chimps were seen to make gentle “hoo” sounds to those behind them when they came across the model viper or see fresh faeces from predators.

Dr Catherine Crockford who led the study, said: “Lots of animals give alarm calls and are more likely to do so if there’s an audience, but these chimps are more likely to call if the audience doesn’t know about the danger. It’s as if they’re picking up on differences in ignorance and knowledge in others.”

In video footage recorded, chimps who were leading the group were initially startled when seeing the fake snake, then after regaining composure would “hoo” the most to those following behind who’d been too far away to see the snake or hear their earlier warning calls. And the chimps “hoo-ed” the least when other chimps had seen the fake snake themselves.

This behaviour suggests that the primates knew what their companions knew and made decisions based on that information.

Dr Crockford added: “The chimps would sometimes jump when they saw the snake, but they didn’t call then. They would only call after going back for a second look. So there’s a dissociation between their emotional reaction and the vocalisation. The call is not a knee jerk reaction to the snake, it’s intelligent behaviour.”

The study published in Current Biology was carried out by the  Max Planck Institute for Evolutionary Anthropology in Leipzig and the Budongo Conservation Field Station in Uganda.