Honest signals Eurasian jay, Garrulus glandarius, gives honest signals-loud alarm calls-from its tree perch when it sees a predator.įurther information: Unconscious communication, Reciprocal altruism, Handicap principle, and Aposematism Signallers have sometimes evolved multiple sexual ornaments, and receivers have sometimes evolved multiple trait preferences. The sensory exploitation hypothesis proposes that pre-existing preferences in female receivers can drive the evolution of signal innovation in male senders, in a similar way to the hidden preference hypothesis which proposes that successful calls are better able to match some 'hidden preference' in the female. Various hypotheses seek to explain why females would select for one call over the other. The signal can be the call itself, the intensity of a call, its variation style, its repetition rate, and so on. Once a female chooses a mate, this selects for a specific style of male calling, thus propagating a specific signalling ability. For example, the male gray tree frog, Hyla versicolor, produces a call to attract females. When animals choose mating partners, traits such as signalling are subject to evolutionary pressure. The same mechanisms can be expected in humans, where researchers have studied behaviours including risk-taking by young men, hunting of large game animals, and costly religious rituals, finding that these appear to qualify as costly honest signals. The evolutionary equilibrium depends sensitively on the balance of costs and benefits. The mathematical biologist Ronald Fisher analysed the contribution that having two copies of each gene ( diploidy) would make to honest signalling, demonstrating that a runaway effect could occur in sexual selection. Biologists have attempted to verify the handicap principle, but with inconsistent results. The system is evolutionarily stable as the large showy tails are honest signals. According to Zahavi's theory, signallers such as male peacocks have "tails" that are genuinely handicaps, being costly to produce. Amotz Zahavi suggested that cheating could be controlled by the handicap principle, where the best horse in a handicap race is the one carrying the largest handicap weight. The question of whether the selection of signals works at the level of the individual organism or gene, or at the level of the group, has been debated by biologists such as Richard Dawkins, arguing that individuals evolve to signal and to receive signals better, including resisting manipulation. 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. Signals may be honest, conveying information which usefully increases the fitness of the receiver, or dishonest. Signals thus evolve because they modify the behaviour of the receiver to benefit the signaller. Signals are given in contexts such as mate selection by females, which subjects the advertising males' signals to selective pressure. Mathematical models describe how signalling can contribute to an evolutionarily stable strategy. The central question is when organisms with conflicting interests, such as in sexual selection, should be expected to provide honest signals (no presumption being made of conscious intention) rather than cheating. Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals, both within species and across species. For the engineering concept, see signal theory.īy stotting (also called pronking), a springbok ( Antidorcas marsupialis) signals honestly to predators that it is young, fit, and not worth chasing. For the analogous theory in economics, see signalling (economics). This article is about signalling in evolutionary biology.
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