Conservatism and "copy-if-better" in chimpanzees (Pan troglodytes)

Abstract

Social learning is predicted to evolve in socially living animals provided the learning process is not random but biased by certain socio-ecological factors. One bias of particular interest for the emergence of (cumulative) culture is the tendency to forgo personal behaviour in favour of relatively better variants observed in others, also known as the "copy-if-better" strategy. We investigated whether chimpanzees employ copy-if-better in a simple token-exchange paradigm controlling for individual and random social learning. After being trained on one token-type, subjects were confronted with a conspecific demonstrator who either received the same food reward as the subject (control condition) or a higher value food reward than the subject (test condition) for exchanging another token-type. In general, the chimpanzees persisted in exchanging the token-type they were trained on individually, indicating a form of conservatism consistent with previous studies. However, the chimpanzees were more inclined to copy the demonstrator in the test compared to the control condition, indicating a tendency to employ a copy-if-better strategy. We discuss the validity of our results by considering alternative explanations and relate our findings to the emergence of cumulative culture.

Keywords: Chimpanzees; Culture; Decision-making; Social learning.

Fig. 1

Depicted are a the demonstrator exchanging a rectangle-shaped token with the experimenter for a piece of carrot, and subsequently b the subject exchanging a trapezium-shaped token with the experimenter for a piece of carrot. The subject (on the left in both figures) had a private token container available, comprising three compartments holding ~40 tokens of the depicted token-type each. The demonstrator had the same token container available, yet was only able to obtain one particular token-type (here: rectangle-shaped). In order to make the demonstrator’s exchanges and associated food rewards conspicuous to the subject, the experimenter held the exchanged token and the food reward in the air for ~2 s after which he gave the reward to the demonstrator and placed the exchanged token on the table (largest grey rectangle). After any exchange, the experimenter would block the used exchange hole with a piece of perspex (black vertical line) and orient his body towards the other chimpanzee in anticipation of a new exchange. In the test condition, the demonstrator received one piece of banana instead of carrot per exchanged token. All food rewards were hidden underneath the table, out of sight of both chimpanzees

Fig. 2

Subjects’ token choices (mean proportion ± s.e.m) for a all data, b the first trial after having observed the demonstrator receiving either the same reward as the subject (control condition) or a higher value reward (test condition) for using a different token-type