Chimpanzees Help Each Other upon Request

利他行動の進化的起源 - チンパンジーは要求に応じて相手を助ける -. 京都大学プレスリリース. 2009-10-14. http://www.kyoto-u.ac.jp/ja/news_data/h/h1/news6/2009/091014_1.htmBackground: The evolution of altruism has been explained mainly from ultimate perspectives. However, it remains to beinvestigated from a proximate point of view how and in which situations such social propensity is achieved. We investigatedchimpanzees’ targeted helping in a tool transfer paradigm, and discuss the similarities and differences in altruism betweenhumans and chimpanzees. Previously it has been suggested that chimpanzees help human experimenters by retrieving anobject which the experimenter is trying to reach. In the present study, we investigated the importance of communicativeinteractions between chimpanzees themselves and the influence of conspecific partner’s request on chimpanzees’ targetedhelping.Methodology/Principal Findings: We presented two tool-use situations (a stick-use situation and a straw-use situation) intwo adjacent booths, and supplied non-corresponding tools to paired chimpanzees in the two booths. For example, achimpanzee in the stick-use situation was supplied with a straw, and the partner in the straw-use situation possessed a stick.Spontaneous tool transfer was observed between paired chimpanzees. The tool transfer events occurred predominantlyfollowing recipients’ request. Even without any hope of reciprocation from the partner, the chimpanzees continued to helpthe partner as long as the partner required help.Conclusions/Significance: These results provide further evidence for altruistic helping in chimpanzees in the absence ofdirect personal gain or even immediate reciprocation. Our findings additionally highlight the importance of request as aproximate mechanism motivating prosocial behavior in chimpanzees whether between kin or non-kin individuals and thepossible confounding effect of dominance on the symmetry of such interactions. Finally, in contrast to humans, our studysuggests that chimpanzees rarely perform acts of voluntary altruism. Voluntary altruism in chimpanzees is not necessarilyprompted by simple observation of another’s struggle to attain a goal and therefore an accurate understanding of others’desires in the absence of communicative signals.