Handicap principle
[5][6][7][8][9] The handicap principle is supported by game theory modelling representing situations such as nestlings begging for food, predator-deterrent signalling, and threat displays.
However, honest signals are not necessarily costly, undermining the theoretical basis for the handicap principle, which remains unconfirmed by empirical evidence.
[2][3][10] The generality of the phenomenon is a matter of some debate and disagreement, and Zahavi's views on the scope and importance of handicaps in biology have not been accepted by the mainstream.
[13][14][15] The handicap principle was initially controversial,[5][6][7][8] with the British biologist John Maynard Smith a notable early critic of Zahavi's ideas.
[1] A series of papers by the American biologist Thomas Getty showed that Grafen's proof of the handicap principle depends on the critical, simplifying assumption that signallers trade off costs for benefits in an additive fashion, analogous to the way humans invest money to increase income in the same currency.
[26][27] In the classic handicap models of begging in game theory, all players are assumed to pay the same amount to produce a signal of a given level of intensity, but differ in the relative value of eliciting the desired response (donation) from the receiver.
Models of signals (such as threat displays) without any handicapping costs show that what biologists call cheap talk may be an evolutionarily stable form of communication.
[38] Dustin J. Penn and Szabolcs Számadó stated in 2019 that there was still no empirical evidence for evolutionary pressure for wasteful biology or acts, and proposed that the handicap principle should be abandoned.
[39] The handicap principle predicts that a sexual ornament, or any other signal such as visibly risky behavior, must be costly if it is to accurately advertise a trait of relevance to an individual with conflicting interests.
American scientist Jared Diamond has proposed that certain risky human behaviours, such as bungee jumping, may be expressions of instincts that have evolved through the operation of the handicap principle.
[41] The handicap principle gains further support by providing interpretations for behaviours that fit into a single unifying gene-centered view of evolution and making earlier explanations based on group selection obsolete.
[42][43][44] French biologist Patrice David showed that in the stalk-eyed fly species Cyrtodiopsis dalmanni, genetic variation underlies the response to environmental stress, such as variable food quality, of a male sexual ornament, eye span.
[47] Another example is provided by larks, some of which discourage merlins by sending a similar message: they sing while being chased, telling their predator that they will be difficult to capture.
[52] Healthy individuals can afford to suppress their immune system by raising their testosterone levels, at the same time augmenting secondary sexual traits and displays.
