page_title: Signalling theory
section_title: Sports handicapping metaphor
hierarchical_section_title: Signalling theory / Sports handicapping metaphor
caption_attribution_description: Image by Heather Abounader www.abounaderphoto.com
context_page_description: Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. The central question is when organisms with conflicting interests, such as in sexual selection, should be expected to provide honest signals rather than cheating. Mathematical models describe how signalling can contribute to an evolutionarily stable strategy.
  Signals are given in contexts such as mate selection by females, which subjects the advertising males' signals to selective pressure. Signals thus evolve because they modify the behaviour of the receiver to benefit the signaller. Signals may be honest, conveying information which usefully increases the fitness of the receiver, or dishonest. An individual can cheat by giving a dishonest signal, which might briefly benefit that signaller, at the risk of undermining the signalling system for the whole population.
context_section_description: In 1975, Amotz Zahavi proposed a verbal model for how signal costs could constrain cheating and stabilize an "honest" correlation between observed signals and unobservable qualities, based on an analogy to sports handicapping systems. He called this idea the handicap principle. The purpose of a sports handicapping system is to reduce disparities in performance, making the contest more competitive. In a handicap race, intrinsically faster horses are given heavier weights to carry under their saddles. Similarly, in amateur golf, better golfers have fewer strokes subtracted from their raw scores. This creates correlations between the handicap and unhandicapped performance, if the handicaps work as they are supposed to, between the handicap imposed and the corresponding horse's handicapped performance. If you knew nothing about two race horses or two amateur golfers except their handicaps, you could infer which is most likely to win: the horse with the bigger weight handicap, and the golfer with the smaller stroke handicap. By analogy, if peacock 'tails' (large tail covert feathers) act as a handicapping system, and a peahen knew nothing about two peacocks but the sizes of their tails, she could "infer" that the peacock with the bigger tail has greater unobservable intrinsic quality. Display costs can include extrinsic social costs, in the form of testing and punishment by rivals, as well as intrinsic production costs. Another example given in textbooks is the extinct Irish elk, Megaloceros giganteus. The male Irish elk's enormous antlers could perhaps have evolved as displays of ability to overcome handicap, though biologists point out that if the handicap is inherited, its genes ought to be selected against.
  The essential idea here is intuitive and probably qualifies as folk wisdom. It was articulated by Kurt Vonnegut in his 1961 short story Harrison Bergeron. In Vonnegut's futuristic dystopia, the Handicapper General uses a variety of handicapping mechanisms to reduce inequalities in performance. A spectator at a ballet comments: "it was easy to see that she was the strongest and most graceful of all dancers, for her handicap bags were as big as those worn by two hundred pound men." Zahavi interpreted this analogy to mean that higher quality peacocks with bigger tails are signalling their ability to "waste" more of some resource by trading it off for a bigger tail. This resonates with Thorstein Veblen's idea that conspicuous consumption and extravagant status symbols can signal wealth.
  Zahavi's conclusions rest on his verbal interpretation of a metaphor, and initially the handicap principle was not well received by evolutionary biologists. However, in 1984, Nur and Hasson used life history theory to show how differences in signalling costs, in the form of survival-reproduction tradeoffs, could stabilize a signalling system roughly as Zahavi imagined. Genetic models also suggested this was possible. In 1990 Alan Grafen showed that a handicap-like signalling system was evolutionarily stable if higher quality signallers paid lower marginal survival costs for their signals.
  In 1982, W.D. Hamilton proposed a specific but widely applicable handicap mechanism, parasite-mediated sexual selection. He argued that in the never-ending co-evolutionary race between hosts and their parasites, sexually selected signals indicate health. This idea was tested in 1994 in barn swallows, a species where males have long tail streamers. Møller found that the males with longer tails, and their offspring, did have fewer bloodsucking mites, whereas fostered young did not. The effect was therefore genetic, confirming Hamilton's theory.
  Another example is Lozano's hypothesis that carotenoids have dual but mutually incompatible roles in immune function and signalling. Given that animals cannot synthesize carotenoids de novo, these must be obtained from food. The hypothesis states that animals with carotenoid-depended sexual signals are demonstrating their ability to "waste" carotenoids on sexual signals at the expense of their immune system.
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caption: The best horses in a handicap race carry the largest weights, so the size of the handicap is a measure of the animal's quality.
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