Phelps, Steve

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 consistsof an equal duration of effort (e.g. twenty seconds of grooming repaid withtwenty seconds of grooming). Here, we report a study of allogrooming in a group of twenty-six captive chimpanzees (Chester Zoo, UK), on more than 150hours 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 forsome 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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Precise time-matching in chimpanzee allogrooming does not exist after a short delay

https://kclpure.kcl.ac.uk/portal/files/102175844/Precise_time_matching_in_chimpanzee_PHELPS_Published11September2018_GOLD_VoR_CC_BY_.pdf

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

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