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The handicap principle is a hypothesis proposed by biologist Amotz Zahavi[1][2][3] 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[4]. Nevertheless, the idea has been very influential[5][6][7], with most researchers in the field believing that the theory explains some aspects of animal communication.

Peacock front02 - melbourne zoo

Fig. 1 - The Peacock's train, the classic example of a handicapped signal of male quality.

Though the idea was initially controversial[8][9][10][11] (John Maynard Smith being one notable early critic of Zahavi's ideas[12][13][14]), it has gained wider acceptance due to supporting game theoretic models, most notably Alan Grafen's signalling game model[15]. Gafen's model is essentially a rediscovery of Michael Spence's job market signalling model[16], 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[17] predator deterrent signals[18] and threat displays[19][20].

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.


  1. Zahavi, A. (1975) Mate selection - a selection for a handicap. Journal of Theoretical Biology 53: 205-214.
  2. Zahavi, A. (1977) The cost of honesty (Further remarks on the handicap principle). Journal of Theoretical Biology 67: 603-605.
  3. Zahavi, A. and Zahavi, A. (1997) The handicap principle: a missing piece of Darwin's puzzle. Oxford University Press. Oxford. ISBN 0-19-510035-2
  4. Andrew Pomiankowski, A. & Iwasa, Y. 1998. Handicap Signaling: Loud and True? Evolution, 52, 928-932
  5. Johnstone, R.A. (1995) Sexual selection, honest advertisement and the handicap principle: reviewing the evidence" Biological Reviews 70 1-65.
  6. Johnstone, R.A. (1997) The evolution of animal signals, In Behavioural Ecology: an evolutionary approach 4th ed., J. R. Krebs and N. B. Davies, editors. Blackwell. Oxford, pp:155-178.
  7. Maynard Smith, J. and Harper, D. (2003) Animal Signals. Oxford University Press. ISBN 0-19-852685-7.
  8. Davis, J. W. F., & O’Donald, P. (1976). Sexual selection for a handicap: A critical analysis of Zahavi’s model. Journal of Theoretical Biology, 57, 345–354.
  9. Eshel, I. (1978). On the handicap principle — a critical defence. Journal of Theoretical Biology, 70, 245–250
  10. Kirkpatrick, M (1986) The handicap mechanism of sexual selection does not work. American Naturalist 127:222-240.
  11. Pomiankowski, A. (1987). Sexual selection: The handicap principle does work sometimes. Proc. R. Soc. Lond., Series B, 231, 123–145.
  12. Maynard Smith, J. (1976). Sexual selection and the handicap principle. Journal of Theoretical Biology, 57, 239–242
  13. Maynard Smith, J. (1978). The handicap principle — a comment. Journal of Theoretical Biology,70, 251–252
  14. Maynard Smith, J. (1985). Mini review: Sexual selection, handicaps and true fitness. Journal of Theoretical Biology, 115, 1–8.
  15. Grafen, A. (1990) Biological signals as handicaps. Journal of Theoretical Biology 144:517-546.
  16. Spence, A.M. (1973) Job Market Signaling. Quarterly Journal of Economics 87:355-374.
  17. Godfray, H.C.J. 1991. Signalling of need by offspring to their parents, Nature 352 328-330.
  18. Yachi, S. 1995. How can honest signalling evolve? The role of the handicap principle. Proceedings of the Royal Society of London, series B 262 283-288.
  19. Adams, E.S. & Mesterton-Gibbons, M. 1995. The cost of threat displays and the stability of deceptive communication. Journal of Theoretical Biology 175 405-421.
  20. Kim, Y-G. 1995. Status signalling games in animal contests. Journal of Theoretical Biology 176, 221-231.

External links[]

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