Secondary sex characteristic

A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system.^[1] In humans, these characteristics typically start to appear during puberty. In animals, they can start to appear at sexual maturity.^[2]^[3] In humans, secondary sex characteristics include enlarged breasts and widened hips of females, facial hair and Adam's apples on males, and pubic hair on both.^[1]^[4] In non-human animals, secondary sex characteristics include, for example, the manes of male lions,^[3] the bright facial and rump coloration of male mandrills, and horns in many goats and antelopes.

Secondary sex characteristics are particularly evident in the sexually dimorphic phenotypic traits that distinguish the sexes of a species.^[5] In evolution, secondary sex characteristics are the product of sexual selection for traits that show fitness, giving an organism an advantage over its rivals in courtship and in aggressive interactions.^[6]

Many characteristics are believed to have been established by a positive feedback loop known as the Fisherian runaway produced by the secondary characteristic in one sex and the desire for that characteristic in the other sex. Male birds and fish of many species have brighter coloration or other external ornaments. Differences in size between sexes are also considered secondary sexual characteristics.

^ ^a ^b Bjorklund DF, Blasi CH (2011). Child and Adolescent Development: An Integrated Approach. Cengage Learning. pp. 152–153. ISBN 978-1133168379.
^ Melmed S, Polonsky KS, Larsen PR, Kronenberg HM (2011). Williams Textbook of Endocrinology E-Book. Elsevier Health Sciences. p. 1054. ISBN 978-1437736007.
^ ^a ^b Pack PE (2016). CliffsNotes AP Biology (5th ed.). Houghton Mifflin Harcourt. p. 219. ISBN 978-0544784178.
^ Rizzo DC (2015). Fundamentals of Anatomy and Physiology. Cengage Learning. pp. 483–484. ISBN 978-1305445420. Archived from the original on April 9, 2023. Retrieved October 14, 2019.
^ Norris DO, Lopez KH (2010). Hormones and Reproduction of Vertebrates, Volume 1. Academic Press. p. 87. ISBN 978-0080958095. Archived from the original on April 9, 2023. Retrieved October 14, 2019.
^ Campbell B (2017). Human Evolution: An Introduction to Man's Adaptations. Routledge. pp. 392–393. ISBN 978-1351514415. Archived from the original on April 9, 2023. Retrieved October 14, 2019.

[Bjorklund-1] Bjorklund DF, Blasi CH (2011). Child and Adolescent Development: An Integrated Approach. Cengage Learning. pp. 152–153. ISBN 978-1133168379.

[Melmed-2] Melmed S, Polonsky KS, Larsen PR, Kronenberg HM (2011). Williams Textbook of Endocrinology E-Book. Elsevier Health Sciences. p. 1054. ISBN 978-1437736007.

[Pack-3] Pack PE (2016). CliffsNotes AP Biology (5th ed.). Houghton Mifflin Harcourt. p. 219. ISBN 978-0544784178.

[Rizzo-4] Rizzo DC (2015). Fundamentals of Anatomy and Physiology. Cengage Learning. pp. 483–484. ISBN 978-1305445420. Archived from the original on April 9, 2023. Retrieved October 14, 2019.

[Norris-5] Norris DO, Lopez KH (2010). Hormones and Reproduction of Vertebrates, Volume 1. Academic Press. p. 87. ISBN 978-0080958095. Archived from the original on April 9, 2023. Retrieved October 14, 2019.

[Campbell-6] Campbell B (2017). Human Evolution: An Introduction to Man's Adaptations. Routledge. pp. 392–393. ISBN 978-1351514415. Archived from the original on April 9, 2023. Retrieved October 14, 2019.

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