Handicap principle
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 sexually selected 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 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. Zahavi's views on the scope and importance of handicaps in biology remain outside the mainstream, never-the-less most researchers in the field believing the theory explains some aspects of animal communication. It also suggests that sexual ornaments should be costly to be attractive, so that they can accurately advertise biological fitness: typical examples are bird songs, the peacock's tail, courtship danses, bowerbird's bowers, or even possibly jewellery and humor.
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.
References
- 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.
- Eshel, I. (1978). On the handicap principle — a critical defence. Journal of Theoretical Biology, 70, 245–250
- Grafen, A. (1990) Biological signals as handicaps. Journal of Theoretical Biology 144:517-546.
- Johnstone, R. A. (1995) Sexual selection, honest advertisement and the handicap principle: reviewing the evidence" Biological Reviews 70:1-65.
- 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.
- Kirkpatrick, M (1986) The handicap mechanism of sexual selection does not work. American Naturalist 127:222-240.
- Maynard Smith, J. (1976). Sexual selection and the handicap principle. Journal of Theoretical Biology, 57, 239–242
- Maynard Smith, J. (1978). The handicap principle — a comment. Journal of Theoretical Biology,70, 251–252
- Maynard Smith, J. (1985). Mini review: Sexual selection, handicaps and true fitness. Journal of Theoretical Biology, 115, 1–8.
- Maynard Smith, J. and Harper, D. (2003) Animal Signals. Oxford University Press. ISBN 0198526857
- Pomiankowski, A. (1987). Sexual selection: The handicap principle does work sometimes. Proc. R. Soc. Lond., Series B, 231, 123–145.
- Zahavi, A. (1975) Mate selection - a selection for a handicap. Journal of Theoretical Biology 53: 205-214.
- Zahavi, A. (1977) The cost of honesty (Further remarks on the handicap principle). Journal of Theoretical Biology 67: 603-605.
- Zahavi, A. and Zahavi, A. (1997) The handicap principle: a missing piece of Darwin's puzzle. Oxford University Press. Oxford. ISBN 0195100352