Chimpanzees return favors at a personal cost.
Abstract
Humans regularly provide others with resources at a personal cost to themselves. Chimpanzees
engage in some cooperative behaviors in the wild as well, but their motivational underpinnings
are unclear. In three experiments, chimpanzees (Pan troglodytes) always chose between
an option delivering food both to themselves and a partner and one delivering food
only to themselves. In one condition, a conspecific partner had just previously taken
a personal risk to make this choice available. In another condition, no assistance
from the partner preceded the subject's decision. Chimpanzees made significantly more
prosocial choices after receiving their partner's assistance than when no assistance
was given (experiment 1) and, crucially, this was the case even when choosing the
prosocial option was materially costly for the subject (experiment 2). Moreover, subjects
appeared sensitive to the risk of their partner's assistance and chose prosocially
more often when their partner risked losing food by helping (experiment 3). These
findings demonstrate experimentally that chimpanzees are willing to incur a material
cost to deliver rewards to a conspecific, but only if that conspecific previously
assisted them, and particularly when this assistance was risky. Some key motivations
involved in human cooperation thus may have deeper phylogenetic roots than previously
suspected.
Type
Journal articlePermalink
https://hdl.handle.net/10161/14983Published Version (Please cite this version)
10.1073/pnas.1700351114Publication Info
Schmelz, Martin; Grueneisen, Sebastian; Kabalak, Alihan; Jost, Jürgen; & Tomasello,
Michael (2017). Chimpanzees return favors at a personal cost. Proc Natl Acad Sci U S A. 10.1073/pnas.1700351114. Retrieved from https://hdl.handle.net/10161/14983.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Michael Tomasello
James F. Bonk Distinguished Professor
Major research interests in processes of social cognition, social learning, cooperation,
and communication from developmental, comparative, and cultural perspectives. Current
theoretical focus on processes of shared intentionality. Empirical research mainly
with human children from 1 to 4 years of age and great apes.

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