Touch-screen-guided task reveals a prosocial choice tendency by chimpanzees ( Pan troglodytes)

PeerJ. 2018 Jul 31;6:e5315. doi: 10.7717/peerj.5315. eCollection 2018.

Abstract

Humans help others even without direct benefit for themselves. However, the nature of altruistic (i.e., only the other benefits) and prosocial (i.e., self and other both benefit) behaviors in our closest living relative, the chimpanzee, remains controversial. To address this further, we developed a touch-screen-guided task that allowed us to increase the number of trials for a thorough test of chimpanzees' prosocial and altruistic tendencies. Mother-offspring dyads were tested in the same compartment; one was the actor while the other was the recipient. In Experiment 1, the actor chose among three options: prosocial, selfish (only the actor benefited) and altruistic. To better understand the nature of the chimpanzees' choices and to improve experimental control, we conducted two additional experiments. Experiment 2 consisted of two-option choices interspersed with three-option choices, and in Experiment 3 the two-option choice were blocked across all trials. The results of Experiment 1 clearly showed that chimpanzees acted prosocially in the touch-screen-guided task, choosing the prosocial option on an average of 79% of choices. Five out of the six chimpanzees showed the preference to act prosocially against chance level. The preference for the prosocial option persisted when conditions were changed in Experiments 2 and 3. When only selfish and altruistic options were available in Experiments 2 and 3, chimpanzees preferred the selfish option. These results suggest that (1) most individuals understood the nature of the task and modified their behavior according to the available options, (2) five out of the six chimpanzees chose to act prosocially when they had the option to, and (3) offspring counterbalanced between altruistic and selfish, when given those two options perhaps to avoid suffering repercussions from the mother.

Keywords: Altruism; Great apes; Other regarding; Prosociality.

Grant support

This research was supported by Grant-in-Aid for Specially Promoted Research: No. 24000001, (PI: Tetsuro Matsuzawa) by the Ministry of Education, Science, Sports and Culture, Japan to both Tetsuro Matsuzawa and Ikuma Adachi: Grant-in-Aids for Scientific Research (S): No. 16H06283, (PI: Masaki Tomonaga), and for Young Scientists (B): No. 22700270 to Ikuma Adachi, the Japan Society for the Promotion of Science (JSPS) to Christoph D. Dahl. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.