Abstract
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.
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.
| Original language | English |
|---|---|
| Journal | PloS one |
| Volume | 13 |
| Issue number | 9 |
| DOIs | |
| Publication status | Published - 11 Sept 2018 |