UMD BIOL 608W - Spontaneous Altruism by Chimpanzees and Young Children

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Spontaneous Altruism by Chimpanzeesand Young ChildrenFelix Warneken*, Brian Hare, Alicia P. Melis, Daniel Hanus, Michael TomaselloDepartment of Developmental and Comparative Psychology, Max Planck Institute for Evolutionary Anthropology, Leipzig, GermanyPeople often act on behalf of others. They do so without immediate personal gain, at cost to themselves, and eventoward unfamiliar individuals. Many researchers have claimed that such altruism emanates from a species-uniquepsychology not found in humans’ closest living evolutionary relatives, such as the chimpanzee. In favor of this view,the few experimental studies on altruism in chimpanzees have produced mostly negative results. In contrast, we reportexperimental evidence that chimpanzees perform basic forms of helping in the absence of rewards spontaneously andrepeatedly toward humans and conspecifics. In two comparative studies, semi–free ranging chimpanzees helped anunfamiliar human to the same degree as did human infants, irrespective of being rewarded (experiment 1) or whetherthe helping was costly (experiment 2). In a third study, chimpanzees helped an unrelated conspecific gain access tofood in a novel situation that required subjects to use a newly acquired skill on behalf of another individual. Theseresults indicate that chimpanzees share crucial aspects of altruism with humans, suggesting that the roots of humanaltruism may go deeper than previous experimental evidence suggested.Citation: Warneken F, Hare B, Melis AP, Hanus D, Tomasello M (2007) Spontaneous altruism by chimpanzees and young children. PLoS Biol 5(7): e184. doi:10.1371/journal.pbio.0050184IntroductionIndividuals of many primate species perform behaviorsthat benefit other individuals. In particular, chimpanzeesengage in behaviors such as food sharing, grooming ,consolation, or coalition formation [1–6]. Most of theseinstances, however, can likely be explained by direct orindirect benefits for the actor through mechanisms such asmutualism or kin selection [7–8]. Humans, in contrast,occasionally help other individuals, even strangers, withoutimmediate benefit for themselves, encompassing situationsthat make reciprocation unlikely [9–10].Many researchers have claimed that such altruism is uniqueto humans, emanating from a species-unique psychology [10–12]. More specifically, chimpanzees (one of human’s twoclosest living primate relatives) are often conceived as lackingthe propensity to act altruistically. Only humans are supposedto develop altruistic behaviors during ontogeny, whereaschimpanzees might only be guided by self-interest. In favor ofthis view, in two recent experiments [12,13], chimpanzeesshowed no other-rega rding tendencies when they coulddeliver food to another chimpanzee. Chimpanzees did notseem to care about the welfare of a conspecific in this food-retrieval context.In contrast, observational studies have provided manyexamples of other-regarding, possibly altruistic behaviors [1–6,14]. In support of these observations, a recent experimentalstudy [15] showed that human-raised chimpanzees providedunrewarded helping behaviors toward their human caregiverby fetching object s she was unsuccessfully reaching for,providing the first experimental evidence for altruistichelping in chimpanzees.Current research thus suggests the possibility that chim-panzees are able and willing to help, but they display thisbehavior only in very restricted contexts. First, chimpanzeesmight help only a familiar human caregiver with whom theymaintained a close relationship, based on a rearing history inwhich compliant behavior in other contexts h ad beenreinforced [15]. Second, chimpanzees might help others onlyif costs are low, whereas humans display much more costlyhelping. In all experimental studies thus far, chimpanzees didnot have to put much effort (energetic costs) into helping bypulling a mechanism or picking up an object. Third, it is stillunclear from experiments whether chimpanzees will helpanother chimpanzee [16]. In previous experiments chimpan-zees did not help when the beneficiary was a conspecific. It ispossible that helping among chimpanzees is limited, becausetheir relationships are often characterized by competition,especially over monopolizable food [17,18], whereas thisconstraint is lifted during interactions with humans whodeliver food rather than compete over it. Alternatively, inthese studies, chimpanzees might not have helped anotherchimpanzee because they were preoccupied with retrievingfood for themselves, and the recipient did nothing to indicateany need for help. The current set of experiments wasdesigned to address these issues.Results and DiscussionExperiment 1In the first experiment, we compared the helpfulness ofchimpanzees and human infants toward unfamiliar individ-uals. Subjects were 36 semi–free ranging chimpanzees born inthe wild who were tested by a human with whom they hadvirtually no prior interaction (no training, no feeding, noAcademic Editor: Frans B. M. de Waal, Emory University, United States of AmericaReceived February 8, 2007; Accepted May 14, 2007; Published June 26, 2007Copyright: Ó 2007 Warneken et al. This is an open-access article distributed underthe terms of the Creative Commons Attribution License, which pe rmits unrestricteduse, distribution, and reproduction in any medium, provided the original authorand source are credited.Abbreviations: E1, experimenter 1* To whom correspondence should be addressed. E-mail: [email protected] Biology | www.plosbiology.org July 2007 | Volume 5 | Issue 7 | e1841414PLoSBIOLOGYprevious testing). In addition, 36 18-mo-old human infants(same age as in [15]) were tested by an unfamiliar adult in asimilar context, allowing a direct quantitative comparisonbetween species. The general idea of the testing situation wasthat an object was placed out of reach for the recipient, butwithin reach of the subject. Helping consisted of handing theobject to the recipient. To assess the motivations underlyinghelping, we varied whether the recipient made an unsuccess-ful attempt to get the object (reaching versus no reaching)and whether he rewarded the subjects in exchange for theobject (reward versus no reward). If subjects are responsive tothe other’s goal, they should hand the object more often inreaching than in no-reaching conditions. If they are primarilyinterested in their own immediate benefit, they should helpmore often in reward than in no-reward


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UMD BIOL 608W - Spontaneous Altruism by Chimpanzees and Young Children

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