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Precise time-matching in chimpanzee allogrooming does not exist after a short delay

Research output: Contribution to journalArticle

Steve Phelps, Wing Lon Ng, Mirco Musolesi, Yvan I. Russell

Original languageEnglish
JournalPloS one
Issue number9
Publication statusPublished - 11 Sep 2018


King's Authors


Allogrooming is a key aspect of chimpanzee sociality and many studies
have investigated the role of reciprocity in a biological market. One
theoretical form of reciprocity is time-matching, where payback consists
of an equal duration of effort (e.g. twenty seconds of grooming repaid with
twenty seconds of grooming). Here, we report a study of allogrooming in a
group of twenty-six captive chimpanzees (Chester Zoo, UK), on more than 150
hours worth of data. For analysis, we introduce a methodological
innovation called the ``delta scale'', which unidimensionally measures the
accuracy of time-matching according to the extent of delay after the
cessation of grooming. Delta is positive when reciprocation occurs after
any non-zero delay (e.g. A grooms B and then B grooms A after a five
second break) and it is negative when reciprocation begins whilst the
original grooming has not yet ceased. Using a generalised linear
mixed-method with different time windows sampled, and a longitudinal
regression analysis, we did find evidence for time-matched reciprocation.
However, this was true only for immediate reciprocation (delta
less than zero). If there was a temporal break in grooming between two
members of a dyad, then there was no evidence at all that chimpanzees were
using new bouts to retroactively correct for time-matching imbalances from
previous bouts. We did not directly test for contingent reciprocity, but here
we obtained a negative result consistent with the idea that reciprocation
proceeds with a minimum of calculation. Our results have implications for
some of the cognitive constraints that differentiate real-life reciprocation
from abstract theoretical models. Furthermore, we suggest that the
apparent patterns of reciprocity that are widely observed may arise merely
due to the law of large numbers.

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