2015•The International Encyclopedia of Human SexualityRequires access
Sexual dimorphism
Steven J. C. Gaulin, William D. Lassek
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Abstract
Sexual dimorphism (ancient Greek dis : twice; morphē : form) denotes any situation where, on average, the male and the female members of a species differ. Though often used to mark simple size differences between the sexes, the same phrase can also refer to specific anatomical, physiological, psychological, or behavioral sex differences. In any given species, sexual dimorphism can vary greatly across traits. For example, Homo sapiens shows low levels of sexual dimorphism in eye color, moderate sexual dimorphism in height, and high levels of sexual dimorphism in muscle mass. Modern evolutionary theory offers explanations for the diverse patterns of sexual dimorphism observed in nature.