Handicap theory

The handicap principle is a hypothesis originally proposed in 1975 by Israeli biologist Amotz Zahavi to explain how evolution may lead to "honest" or reliable signaling between animals which have an obvious motivation to bluff or deceive each other. The handicap principle suggests that reliable signals must be costly to the signaler, costing the signaler something that could not be afforded by an individual with less of a particular trait. For example, in the case of sexual selection, the theory suggests that animals of greater biological fitness signal this status through handicapping behaviour or morphology that effectively lowers this quality. The central idea is that sexually selected traits function like conspicuous consumption, signalling the ability to afford to squander a resource. Receivers know that the signal indicates quality because inferior quality signallers cannot afford to produce such wastefully extravagant signals.

The generality of the phenomenon is the matter of some debate and disagreement, and Zahavi's views on the scope and importance of handicaps in biology has not been accepted by the mainstream. Nevertheless, the idea has been very influential, with most researchers in the field believing that the theory explains some aspects of animal communication.

Though the handicap principle was initially controversial,—John Maynard Smith being one notable early critic of Zahavi's ideas—it has gained wider acceptance because it is supported by game theoretic models, most notably Alan Grafen's signalling game model. Grafen's model is essentially a rediscovery of Michael Spence's job market signalling model, where the signalled trait was conceived as a courting male's quality, signalled by investment in an extravagant trait—such as the peacock's tail—rather than an employee signalling their quality by way of a costly education. In both cases, it is the decreased cost to higher-quality signallers of producing increased signal that stabilizes the reliability of the signal (Fig. 2).

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