Relationships between fluctuating asymmetry and fitness: how good is the evidence?

A number of recent articles have espoused a relationship between developmental stability, as measured by fluctuating asymmetry, and individual fitness, to the extent that asymmetry has been viewed as a surrogate for more direct fitness assessment. This essay reviews the underlying assumptions and evidence for such a relationship and concludes that although asymmetry assessment may provide a useful early-warning system for detection of individuals and populations under stress, there is inadequate evidence at this stage to support its widespread application as substitute for conventional fitness measurement within conservation programmes.