Darwinian Puzzle

A Darwinian puzzle is a trait that appears to reduce the fitness of individuals that possess it. Such traits attract the attention of evolutionary biologists. The phrase "Darwinian puzzle" itself is rare and of unclear origin; it appears most often, but not always, in the context of animal behavior.

A peacock shows this example of a trait that may reduce its fitness. The bigger the tail, the easier it is seen by predators and it also may hinder the movement of the peacock. Darwin said in fact that this goes into sexual selection and the bigger tail attracts more females allowing its fitness to improve. {http://bcrc.bio.umass.edu/courses/fall2009/biol/biol312section1/node/1230}