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
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]
The characteristics are believed to be produced 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.
Secondary sex characteristics vs. primary sex characteristics
The reproductive organs in male or female mammals that are usually identifiable at birth are described as the primary sex characteristics or
The secondary sex characteristics differ in that they will not be identifiable at birth, they will develop as the subject becomes sexually mature. In mammals, these characteristics include breasts in females and greater muscle mass in males. Secondary sexual characteristics have an evolutionary purpose: increase the chance of breeding.[7]
Evolutionary roots
In
In non-human animals
Examples of secondary sex characteristics in non-human animals include manes of male
Biologists today distinguish between "male-to-male combat" and "mate choice", usually female choice of male mates. Sexual characteristics due to combat are such things as antlers, horns, and greater size. Characteristics due to mate choice, often referred to as ornaments, include brighter plumage, coloration, and other features that have no immediate purpose for survival or combat.[14]
Male jumping spiders have visual patches of UV reflectance, which are ornamentations used to attract females.[15]
In humans
Females
In females,
- Enlargement of
- Growth of body hair, most prominently underarm and pubic hair.[3][1][4]
- Widening of waist to hip ratio than adult males.[20]
- Upper arms approximately 2 cm longer, on average, for a given height.[21]
- vulva, may grow more prominent and undergo changes in color with the increased stimulation related to higher levels of estrogen.[22]
Males
The increased secretion of
- Growth of body hair, including underarm, abdominal, chest, and pubic hair.[3][1]
- Growth of facial hair.[1]
- Enlargement of the larynx (Adam's apple) and deepening of the voice.[1][24]
- Increased stature; adult males are taller than adult females, on average.[1]
- Heavier skull and bone structure.[1]
- Increased muscle mass and strength.[1]
- Broadening of the shoulders and the chest; the shoulders are wider than the hips.[25]
- Increased secretions of the oil and sweat glands.[24]
References
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- ^ Keathley, Christina (July 27, 2021). "Types of Sex Characteristics". study.com. Archived from the original on October 26, 2022. Retrieved October 26, 2022.
- ^ "Sexual selection" Archived September 1, 2022, at the Wayback Machine. Darwin Correspondence Project. University of Cambridge. Retrieved 1 September 2022.
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- ^ "Primary and Secondary Sex Characteristics". Archived from the original on August 3, 2020. Retrieved August 14, 2020.
- ^ Duellman, W.E.; Campbell, J.A. (1992). "Hylid frogs of the genus Plectrohyla: systematics and phylogenetic relationships" (PDF). Museum of Zoology, University of Michigan (181).
- ^ Froese, Rainer; Pauly, Daniel (eds.). "Glossary Search for nuptial tubercle". FishBase glossary.
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- ^ ^ Ronald Fisher in a letter to Charles Galton Darwin, 22 November 1932, cited in Fisher, R. A., Bennett, J. H. 1999. The genetical theory of natural selection: A complete variorum edition, Oxford University Press, Oxford, p. 308
- ^ Lim, Matthew L. M., and Daiqin Li. "Courtship and Male-Male Agonistic Behaviour of Comsophasis Umbratica Simon, an Ornate Jumping Spider (Araneae: Salticidae)." The Raffles Bulletin of Zoology (2004): 52(2): 435-448. National University of Singapore. 20 September 2015
- ISBN 978-1-4831-5171-7. Archivedfrom the original on April 9, 2023. Retrieved March 18, 2018.
The first genetic male child with a defect in 3β-hydroxy-Δ5-steroid oxidoreductase to have reached puberty has been reported to have a high level of 3β-hydroxy-A5 steroid excretion, hypospadias at birth, salt-wasting, and a history of two siblings with congenital adrenal hyperplasia and ambiguous genitalia [33]. Although at puberty he has signs of virilization, he has developed pronounced gynecomastia. Thus, this boy demonstrates that breast development may occur in postpubertal males if the programing of the pubertal sex differentiation of the mammary gland anlagen is disturbed by an enzyme defect which causes a failure of fetal testicular testosterone production. This observation is completely consistent with the findings in the experimental models [11, 32].
- PMID 6070056.
When administered to gravid rats during pregnancy an anti-androgenic steroid [cyproterone acetate] induced development of nipples in male fetuses. These nipples and associated glandular tissues develop after birth as in normal female animals. Progestin-estrogen treatment of adult, castrated feminized males produced stimulation of the glandular tissue similar to that seen after treatment of castrated female animals. In castrated male rats this treatment produces little glandular proliferation. It is concluded that androgens normally prevent the development of nipples and extensive formation of mammary tissue in male fetuses.
- PMID 608453.
Breast tissue of adult male Holtzman rats exposed to cyproterone acetate during embryonic differentiation showed presence of specific estradiol receptor proteins and C-19 steroid aromatase. We reported similar findings in gynecomastia in man. It is therefore proposed that gynecomastia probably results from failure of adequate testosterone action on the breast primordia during embryonic differentiation.
- ISBN 978-0840062253. Archivedfrom the original on April 9, 2023. Retrieved October 14, 2019.
- ISBN 9780429590061. Archivedfrom the original on December 2, 2021. Retrieved December 2, 2021.
- ^ Manwatching: A Field Guide to Human Behaviour, 1977, Desmond Morris
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- ^ a b Sexual reproduction Archived 2009-02-08 at the Wayback Machine
- ^ "Secondary Characteristics". hu-berlin.de. Archived from the original on September 27, 2011.