The Theory of Honest Signalling

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Introduction: Part 1

Introduction: Part 2

The Basic Problem

The Basic Solution

Honest signalling in biology

Zahavi's handicap principle

Grafen's model

Attracting mates

Begging for food

Deterring predation

Contesting resources

Autumn color

Honest signalling in economics

Conspicuous consumption


The mathematics of honest signalling

Signalling as a game


Other resources

Carl T. Bergstrom

Using Mathematica

Contact Information

Department of Zoology
University of Washington
Box 351800
Seattle, WA 98195-1800

Honest signals in biology:
From Zahavi's handicap principle...

In the early 1970's, biologist Amotz Zahavi struggled to understand why animals often produce costly and extravagent displays or physical ornaments. Why to peacocks have such spectacular plumage? Why do baby birds beg so loudly? Why do gazelles jump up and down when they see a lion?

To answer this question, Zahavi proposed that these extravagences are signals to other individuals. For example, a peacock's tail may be a signal used by prospective mates in order to estimate the individual's overall condition and/or genetic quality:

"An individual with a well developed sexually selected character [such as a peacock's flashy tail] is an individual which has survived a test. A female which could discriminate between a male possessing a sexually selected character, from one without it, can discriminate between a male which has passed a test and one which has not been tested. Females which selected males with the most developed characters can be sure that they have selected from among the best genotypes of the male population. " (Zahavi 1975)

Zahavi named his theory "the handicap principle," and suggested that there was something about costly behaviors or physical features that made for inherently reliable signals. But what is it about these costly traits - handicaps, as he called them - that makes them believable?

This became a topic of great debate over the next fifteen years.

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Last modified September 4, 2002
Copyright © 2002 Carl T. Bergstrom