Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

William Hopkins

Second Advisor

Michael Beran

Third Advisor

Sarah Brosnan

Fourth Advisor

Jill Pruetz

Fifth Advisor

David Washburn


A notable difference between the two Pan species is their tool using ability. Though many studies on physical tool use exist, few investigate social tool use and, to my knowledge, none focus on their potential relationship or cognitive foundations.While captive and wild chimpanzees are recognized as proficient tool users, captive bonobos exhibit some tool using skills but evidence in wild bonobos is rare. An important similarity, however, is their flexible and intentional use of communicative signals. Captive bonobos and chimpanzees are known to use their communicative behaviors to manipulate humans to obtain an unreachable food, a form of social tool use. With growing interest in social tool use, an emerging central question is to what extent different species utilize these two tool strategies. Thus, 27 bonobos and 29 chimpanzees were given a physical tool task requiring retrieval of a reward at increasing distances such that the physical tool no longer solved the problem while a human who could be solicited was present. Although both species successfully retrieved rewards with the physical tool and solicited the human, chimpanzees showed greater proficiency and flexibility by making fewer attempts to retrieve rewards, retrieving rewards faster, and making more solicitations. For both species, solicitation behavior was prevalent at further distances where the reward was unable to be retrieved, supporting previous research showing these species intentionally produce attention-getting/directing behaviors to indicate toward desired out-of-reach items. In this study, bonobos and chimpanzees exhibited cognitive flexibility by switching tool strategies from using a physical tool at closer distances to using a social tool (a human) at further distances. Regardless of species, physical and social tool performance was related to performance on previous physical and social cognition tasks, including the Primate Cognition Test Battery. The results of this study support the idea that physical and social cognition may not be two separate cognitive domains, as they are so often treated. Rather, cognition may be a single entity in which certain behaviors and processes are elicited by physical and/or social contexts, allowing the transition between physical and social tool modalities.