Handicap principle

The handicap principle is a hypothesis proposed by biologist Amotz Zahavi  to explain the existence of apparently "honest", or reliable, communication between animals despite the apparent evolutionary advantage to cheating or bluffing. The theory proposes that animals of greater quality communicate this status through behaviour or morphology that imposes a cost which reduces their advantage. The central idea is that sexually selected traits function like conspicuous consumption signalling the ability to afford to squander a resource simply by squandering. 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, Zahavi's views on the scope and importance of handicaps in biology remain outside 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 idea was initially controversial   (John Maynard Smith being one notable early critic of Zahavi's ideas   ), it has gained wider acceptance due to supporting game theoretic models, most notably Alan Grafen's signalling game model. Gafen'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 an expensive education. In both cases, it is the decreased cost to higher quality signallers of producing increased signal that stabilizes the reliability of the signal. Further formal game theoretical signalling models demonstrated the evolutionary stability of handicapped signals in nestling begging calls predator deterrent signals and threat displays.

The theory predicts that sexual ornaments must be costly if they accurately advertise biological fitness. Typical examples of handicapped signals include bird songs, the peacock's tail, courtship dances, bowerbird's bowers, or even possibly jewellery and humor. 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.