title: Is it useful to view the brain as a secondary sexual characteristic?
abstract: Many sex differences in brain and behavior related to reproduction are thought to have evolved based on sexual selection involving direct competition for mates during male-male competition and female choice. Therefore, certain aspects of brain circuitry can be viewed as secondary sexual characteristics. The study of proximate causes reveals that sex differences in the brain of mammals and birds reflect organizational and activational effects of sex steroids as articulated by Young and collaborators. However, sex differences in brain and behavior have been identified in the cognitive domain with no obvious link to reproduction. Recent views of sexual selection advocate for a broader view of how intra-sexual selection might occur including such examples as competition within female populations for resources that facilitate access to mates rather than mating competition per se. Sex differences can also come about for other reasons than sexual selection and recent work on neuroendocrine mechanisms has identified a plethora of ways that the brain can develop in a sex specific manner. Identifying the brain as sexually selected requires careful hypothesis testing so that one can link a sex-biased aspect of a neural trait to a behavior that provides an advantage in a competitive mating situation.
authors.affiliation: Department of Psychological and Brain Sciences, Johns Hopkins University, 3400 N, Charles Street, Baltimore, MD 21218, USA. Electronic address: gball@jhu.edu.
authors.forename: Gregory F
authors.initials: GF
authors.lastname: Ball
authors.affiliation: GIGA Neuroscience, University of Liege, 1 boulevard de l'Hôpital, 4000 Liege, Belgium. Electronic address: jbalthazart@ulg.ac.be.
authors.forename: Jacques
authors.initials: J
authors.lastname: Balthazart
authors.affiliation: Department of Pharmacology, University of Maryland School of Medicine, 655 W. Baltimore Street, Baltimore, MD 21210, USA.
authors.forename: Margaret M
authors.initials: MM
authors.lastname: McCarthy
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D002755:Choice Behavior / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D012098:Reproduction / Q000502:physiology*; D012727:Sex Characteristics; D012919:Social Behavior
keywords: Female competition; Organizing effects of steroids; Sex differences; Sexual differentiation; Sexual selection; Sexually differentiated gene expression