Signalling Theory - Honest Signals

Honest Signals

In biology, signals are traits, including structures and behaviors, that have evolved specifically because they change the behavior of receivers in ways that benefit the signaller. Traits or actions that benefit the receiver exclusively are called cues. When an alert bird deliberately gives a warning call to a stalking predator and the predator gives up the hunt, the sound is a signal. When a foraging bird inadvertently makes a rustling sound in the leaves that attracts predators and increases the risk of predation, the sound is a 'cue'.

Signalling systems are shaped by the extent to which signallers and receivers have mutual interests. An alert bird warning off a stalking predator is communicating something useful to the predator: that it has been detected by the prey; it might as well quit wasting its time stalking this alerted prey, which it is unlikely to catch. When the predator gives up, the signaller can get back to other important tasks. Once the stalking predator is detected, the signalling prey and receiving predator have a mutual interest terminating the hunt.

Within species, mutual interests generally increase with kinship. Kinship is central to models of signalling between relatives, for instance when broods of nestling birds beg and compete for food from their parents. The distinction between signals and cues is not clear, and probably not useful for immune, endocrine and neural signalling between the cells within an individual, at least to the extent that all of these cells are clonal descendents of a fertilized egg and there are no conflicts of interest between them.

The concept of honesty in animal communication is controversial because it is difficult to determine intent and use that as a criterion to discriminate deception from honesty, as we do in human interactions. Because of this, biologists who use the phrase "honest signals" use it in a statistical sense. Biological signals, like warning calls or resplendent tail feathers, are considered honest if they are correlated with, or reliably predict, something useful to the receiver. In this usage, honesty is a useful correlation between the signal trait (which economists call "public information" because it is readily apparent) and the unobservable thing of value to the receiver (which economists refer to as "private information" and biologists often refer to as "quality"). Honest biological signals do not need to be perfectly informative, reducing uncertainty to zero; they only need to be honest "on average" to be potentially useful. Ultimately the value of the signalled information depends on the extent to which it allows the receiver to increase its fitness.