Secondary sex characteristic

Secondary sex characteristic

Secondary sex characteristics are traits that distinguish the two sexes of a species, but that are not directly part of the reproductive system. They are believed to be the product of sexual selection for traits which give an individual an advantage over its rivals in courtship, and aggressive interactions. They are distinguished from the primary sexual characteristics: the sex organs.

Well known secondary sex characteristics include facial hairs of male lions, and long feathers of peacock. In humans, the most visible are breasts of females and beard and moustache of males. Secondary sex characteristics include the tusks of sea lions, the plumage of many male birds, the chemical indicators of many insects, etc.

In humans

Sexual differentiation begins during gestation, when the gonads form. General habitus and shape of body and face, as well as sex hormone levels, are similar in prepubertal boys and girls. As puberty progresses and sex hormone levels rise, differences appear, though puberty causes some similar changes in male and female bodies.

Male levels of testosterone directly induce growth of the testicles and penis, and indirectly (via dihydrotestosterone (DHT)) the prostate. Estradiol and other hormones cause breasts to develop in females. However, fetal or neonatal androgens may modulate later breast development by reducing the capacity of breast tissue to respond to later estrogen.

In males, testosterone directly increases size and mass of muscles, vocal cords, and bones, deepening the voice, and changing the shape of the face and skeleton. Converted into DHT in the skin, it accelerates growth of androgen-responsive facial and body hair, but may slow and eventually stop the growth of head hair. Taller stature is largely a result of later puberty and slower epiphyseal fusion.

In females, breasts are a manifestation of higher levels of estrogen; estrogen also widens the pelvis and increases the amount of body fat in hips, thighs, buttocks, and breasts. Estrogen also induces growth of the uterus, proliferation of the endometrium, and menses.

In humans, secondary sex characteristics include:

*Male
** growth of body hair, including underarm, abdominal, chest, and pubic hair
** growth of facial hair
** enlargement of larynx and deepening of voice [http://www.hartnell.edu/faculty/asteinhardt/mywebs/sexual_reproduction.htm Sexual reproduction ] ]
** increased stature; adult males taller than adult females, on average
** heavier skull and bone structure
** increased muscle mass and strength
** broadening of shoulders and chest; shoulders wider than hips [ [http://www2.hu-berlin.de/sexology/ATLAS_EN/html/secondary_characteristics.html Secondary Characteristics ] ]
** increased secretions of oil and sweat glands, often causing acne and body odor
** coarsening of skin texture
** a prominent Adam's apple
** fat deposits mainly around the abdomen and waistFact|date=June 2007
** higher waist to hip ratio than prepubescent or adult females or prepubescent males, on average
** on average, larger hands and feet than prepubescent or adult females or prepubescent malesFact|date=July 2007
** lower digit ratio, on averageFact|date=October 2007

* Female
** enlargement of breasts [ breasts - [http://www2.hu-berlin.de/sexology/ATLAS_EN/html/secondary_characteristics.html] ]
** growth of body hair, including underarm and pubic hair
** vaginal and uterine growth [ [http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html/] ]
** decreased stature; adult females shorter stature than adult males, on average
** widening of hips [ Hips widen as part of the female pubertal process. [http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html] ] ; lower waist to hip ratio than adult males, on average
** increased secretions of oil and sweat glands, often causing acne and body odor
** changed distribution in weight and fat; more subcutaneous fat and fat deposits mainly around the buttocks, thighs and hips
** higher digit ratio, on averageFact|date=October 2007

ee also

* Puberty
* Virilization
* Sex differences in humans
* Sexual dimorphism

Notes

References

"Sexual Maturity." "Technical Issues in Reproductive Health." Columbia University. May 2, 2008. .

Steinhardt, A. "Sexual Reproduction." Hartnell College. May 2, 2008. .

* http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html
* http://www.hartnell.edu/faculty/asteinhardt/


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  • secondary sex characteristic — n a physical characteristic (as the breasts of a female mammal or the nuptial plumage of a male bird) that appears in members of one sex at puberty or in seasonal breeders at the breeding season and is not directly concerned with reproduction… …   Medical dictionary

  • secondary sex characteristic — n. any of the physical characteristics that differentiate male and female individuals, as distribution of hair or fat on the body, breast and muscle development, deepening of the voice, etc., that are not directly related to reproduction and… …   English World dictionary

  • secondary sex characteristic — noun the genetically determined sex characteristics that are not functionally necessary for reproduction (pitch of the voice and body hair and musculature) • Syn: ↑secondary sexual characteristic, ↑secondary sex character • Hypernyms: ↑sex… …   Useful english dictionary

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  • secondary sex characteristic — Med. any of a number of manifestations, as development of breasts or beard, muscularity, distribution of fat tissue, and change of pitch in voice, specific to each sex and incipient at puberty but not essential to reproduction. Also called… …   Universalium

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