Teaching varies with task complexity in wild chimpanzees

Abstract

Cumulative culture is a transformative force in human evolution, but the social underpinnings of this capacity are debated. Identifying social influences on how chimpanzees acquire tool tasks of differing complexity may help illuminate the evolutionary origins of technology in our own lineage. Humans routinely transfer tools to novices to scaffold their skill development. While tool transfers occur in wild chimpanzees and fulfill criteria for teaching, it is unknown whether this form of helping varies between populations and across tasks. Applying standardized methods, we compared tool transfers during termite gathering by chimpanzees in the Goualougo Triangle, Republic of Congo, and in Gombe, Tanzania. At Goualougo, chimpanzees use multiple, different tool types sequentially, choose specific raw materials, and perform modifications that improve tool efficiency, which could make it challenging for novices to manufacture suitable tools. Termite gathering at Gombe involves a single tool type, fishing probes, which can be manufactured from various materials. Multiple measures indicated population differences in tool-transfer behavior. The rate of transfers and probability of transfer upon request were significantly higher at Goualougo, while resistance to transfers was significantly higher at Gombe. Active transfers of tools in which possessors moved to facilitate possession change upon request occurred only at Goualougo, where they were the most common transfer type. At Gombe, tool requests were typically refused. We suggest that these population differences in tool-transfer behavior may relate to task complexity and that active helping plays an enhanced role in the cultural transmission of complex technology in wild apes.

Keywords: chimpanzee; cumulative culture; prosociality; social learning; tool use.

Fig. 1.

Categorization of transfer types according to the level of prosociality. Transfer types are arranged vertically from most (Top) to least (Bottom) prosocial. Transfers are grouped into 2 categories: requested (blue) in which the potential recipient first requests the tool by whimpering and/or reaching toward the tool, or by making hand-to-mouth gestures; and nonrequested (yellow) in which the recipient receives, takes, or attempts to take the tool without first requesting it. While requested and nonrequested transfer types are presented together, note that Active, Passive, and Hesitant requested transfers may more clearly index prosocial behavior. Requests make the potential recipient’s goal more salient, and they inherently involve a possessor physically relinquishing a tool, while nonrequested transfers are more ambiguous (23). The exception is Proactive transfers, which are the most prosocial because they are initiated by the possessor rather than the recipient. Refusals, and Steal/Failed Steal transfers, are ranked comparably because for each of these, the possessor does not, or does not willingly, relinquish a tool; thus, these are not considered prosocial. Italics indicate that no possession change occurs.

Fig. 2.

Tool-transfer probability and how it depended on tool request status and population. Indicated are the fitted model and its confidence limits (horizontal lines with error bars) and the observed transfer probabilities per possessor. The area of the symbols depicts the number of possessors per population and request status with the same transfer probability, such that larger symbols correspond to a greater number of possessors at that value (range: 1 to 8). NoReq, no request; Req, request.

Fig. 3.

Probability of requested tool transfer and how it differed between populations. Indicated are the fitted model and its confidence limits (horizontal lines with error bars) and the observed transfer probabilities per possessor. The area of the symbols depicts the number of possessors per population with the same transfer probability, such that larger symbols correspond to a greater number of possessors at that value (range: 1 to 8).

Fig. 4.

Resistance probability and how it depended on tool request status and population. Indicated are the fitted model and its confidence limits (horizontal lines with error bars) and the observed transfer probabilities per possessor. The area of the symbols depicts the number of possessors per population and request status with the same transfer probability, such that larger symbols correspond to a greater number of possessors at that value (range: 1 to 11). NoReq, no request; Req, request.