Handicap theory
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The handicap theory is an idea proposed by the Israeli biologist Amotz Zahavi. It concerns the way in which animals communicate through their behaviour, and makes the counterintuitive claim that certain forms of animal behaviour (and features of animal anatomy supporting them) may have evolved because they apparently act to reduce the chances of individual survival of the animal exhibiting the behaviour.
The reasoning supporting this claim depends on considering the question as to how an animal that is the recipient of communication can be assured that the information conveyed is accurate (ie that the signal is honest). The classic example is that of stotting in gazelles. This behaviour consists in the gazelle initially running slowly and jumping high when it is threatened by a predatory lion or cheetah. Traditionally, zoologists had believed that such behaviour might be adapted to alerting other gazelle to a cheetah's presence or might be part of a collective behaviour pattern of the group of gazelle to confuse the cheetah. Instead, Zahavi proposed that each gazelle was communicating to the cheetah that it was a fitter individual than its fellows and that the predator should avoid chasing it. If honest, this claim benefits the cheetah which avoids the wasted energy of a fruitless chase after a healthy animal. The difficulty for the cheetah is how it can know it should trust such an interpretation of the behaviour of stotting. Zahavi's answer is that the signal is reliable precisely because only a fit gazelle can afford to grant the cheetah such an advantage and hope to survive.
Though this idea is recognisable as a generalisation of Charles Darwin's theory of sexual selection, it was initially controversial. However, analysis based on game theoretic computer models demonstrated that it was tenable, and many other examples of the expression of the idea in biology have been suggested.
Jared Diamond has proposed that certain risky human behaviours, such as consumption of addictive drugs and bungee jumping, may be expressions of instincts that have evolved through the operation of the handicap principle.