Chimps don't just blurt out whatever is on their mind - they consider who's listening, says an article published in Current Biology that could reveal an important stage in the development of language.
In a test with 33 chimpanzees and plastic models of vipers, the research team, led by Catherine Crockford from the School of Psychology at the University of St Andrews, found that the apes altered their reactions to a snake according to who was listening.
The chimps were more likely to call out in alarm if they were in the presence of group members unaware of the snake, than if the group members were aware of the snake. The vipers chosen by the boffins have a poisonous bite and tend to stay in the same place for weeks at a time, and the fake snakes were placed in an area that the chimpanzees often used. On first spotting the snake, all the primates jumped away but then returned, looking more closely, and if they were around other apes they believed were not aware of the snake, they emitted a soft "hoo" sound as a warning.
Although many animals make warning sounds on discovering dangers, the findings show something new, according to the abstract of the paper: it highlights that chimps tailored their message according to the audience. And that the chimps understood knowledge and ignorance. The abstract to the paper says:
Some nonhuman primates can read others' intentions and know what others see, but they may not understand that, in others, perception can lead to knowledge.
And it could be a crucial step towards working out how human communication via language started - a process that (in most cases) requires us to understand what is going on in fellow humans' minds:
The ability to recognize other individuals' mental states and their knowledge and beliefs, for example is a fundamental part of human cognition.
The apes are catching up with us. Catherine Crockford et al's Wild Chimpanzees Inform Ignorant Group Members of Danger was published in Current Biology on 29 December. ®