Gossip, or sharing information about absent others, has been identified as an effective
solution to free rider problems in situations with conflicting interests. Yet, the
information transmitted via gossip can be biased, because gossipers may send dishonest
information about others for personal gains. Such dishonest gossip makes reputation-based
cooperation more difficult to evolve. But when are people likely to share honest or
dishonest gossip? We build formal models to provide the theoretical foundation for
individuals' gossip strategies, taking into account the gossiper's fitness interdependence
with the receiver and the target. Our models across four different games suggest a
very simple rule: when there is a perfect match (mismatch) between fitness interdependence
and the effect of honest gossip, the gossiper should always be honest (dishonest);
however, in the case of a partial match, the gossiper should make a choice based on
their fitness interdependence with the receiver and the target and the marginal cost/benefit
in terms of pay-off differences caused by possible choices of the receiver and the
target in the game. Moreover, gossipers can use this simple rule to make optimal decisions
even under noise. We discuss empirical examples that support the predictions of our
model and potential extensions. This article is part of the theme issue 'The language
of cooperation: reputation and honest signalling'.
