Chimpanzees modify intentional gestures to coordinate a search for hidden 1 food 2 Anna

9 Humans routinely communicate to coordinate their activities, persisting and elaborating 10 signals to pursue goals that cannot be accomplished individually. Communicative persistence 11 is associated with uniquely human cognitive skills such as intentionality, because interactants 12 modify their communication in response to another’s understanding of their meaning. Here 13 were show that two language-trained chimpanzees effectively use intentional gestures to 14 coordinate with an experimentally-naïve human to retrieve hidden food, providing some of 15 the most compelling evidence to date for the role of communicative flexibility in successful 16 coordination in nonhumans. Both chimpanzees (Panzee and Sherman) increase the rate of 17 non-indicative gestures when the experimenter approaches the location of the hidden food. 18 Panzee also elaborates her gestures in relation to the experimenter’s pointing, which enables 19 her to find food more effectively than Sherman. Communicative persistence facilitates 20 effective communication during behavioural coordination and is likely to have been 21 important in shaping language evolution. 22