Mate Choice
Fixed Action Patterns
Types of Selection
Background and Environment Affect Phenotype
Testing a Claim about Population Proportion
Natural Selection and Mating Preferences
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Updated: May 10, 2026

Assessing Differences in Sperm Competitive Ability in Drosophila
Published on: August 22, 2013
K G McCracken1, R E Wilson, P J McCracken
1Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA. fnkgm@uaf.edu
The Argentine lake duck possesses the longest bird penis, measuring nearly half a meter and featuring a corkscrew shape. Evolutionary factors may involve sexual selection and female preference for longer or decorated penises.
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