The trade-offs of honest and dishonest signals

Explaining the evolution of honest versus dishonest signals has long posed a major challenge, but several recent developments should spur renewed interest in this problem. First, the Handicap Principle, which maintains that signals must be costly to be honest, has been refuted since the model that claimed to validate this idea has been shown to have been misinterpreted. Second, more recent theoretical models demonstrate that signal honesty can be maintained by condition-dependent signalling trade-offs rather than costs. Third, we propose that signalling trade-offs may provide a general theory of honest signalling under conflicts of interest. According to signalling trade-off theory, signallers that differ in quality face different trade-offs at the honest equilibrium and therefore they are bound to invest differently. Such differential trade-offs, or lack of, can explain honest vs. dishonest signals according to both experiments and models. Signalling trade-offs are found in every example of honest communication in nature under conflict of interest. Moreover, signalling trade-offs couple various fitness components, including both short-term investments into long-term fitness benefits, providing the necessary link between proximate and evolutionary explanations. Furthermore, trade-offs also provide the necessary bridge between biological and economic theories of honest communication, independently developed in parallel for decades.