Secondary sex characteristic
28643
225312623
2008-07-13T01:10:50Z
Noclevername
1546209
text link
[[Image:Peacock.displaying.better.800pix.jpg|right|thumb|300px|A [[peacock]] displays his long, colored [[feather]]s, an example of his secondary sexual characteristics.]]
'''Secondary sex characteristics''' are traits that distinguish the two [[sex]]es 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 [[aggression|aggressive]] interactions. They are distinguished from the [[primary sexual characteristics]]: the [[sex organ]]s.
Well known secondary sex characteristics include facial hairs of male [[lion]]s, 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 [[breast]]s to develop in females. However, fetal or neonatal [[androgen]]s 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 [[muscle]]s, [[vocal cord]]s, and [[bone]]s, deepening the [[human voice|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 [[androgenic alopecia|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 [[menstrual cycle|menses]].
{| style="float:right; background:transparent; padding:20px; margin:0px;"
|[[Image:Woman labeled.jpg|thumb|upright|female sex characteristics]]
|[[Image:Man labeled.jpg|thumb|male sex characteristics]]
|- valign="top"
|}
In humans, secondary sex characteristics include:
*[[Male]]
** growth of [[body hair]], including [[underarm hair|underarm]], [[abdominal hair|abdominal]], [[chest hair|chest]], and [[pubic hair]]
** growth of [[facial hair]]
** enlargement of larynx and deepening of [[human voice|voice]]<ref>[http://www.hartnell.edu/faculty/asteinhardt/mywebs/sexual_reproduction.htm Sexual reproduction<!-- Bot generated title -->]</ref>
** increased [[Human height|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<ref>[http://www2.hu-berlin.de/sexology/ATLAS_EN/html/secondary_characteristics.html Secondary Characteristics<!-- Bot generated title -->]</ref>
** increased secretions of oil and sweat glands, often causing acne and body odor <ref>[http://www.hartnell.edu/faculty/asteinhardt/mywebs/sexual_reproduction.htm Sexual reproduction<!-- Bot generated title -->]</ref>
** coarsening of skin texture
** a prominent [[Adam's apple]]
** [[fat]] deposits mainly around the [[human abdomen|abdomen]] and [[waist]]{{Fact|date=June 2007}}
** higher [[waist-hip ratio|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 males{{Fact|date=July 2007}}
** lower [[digit ratio]], on average{{Fact|date=October 2007}}
* [[Female]]
** enlargement of [[breasts]]<ref> breasts - [http://www2.hu-berlin.de/sexology/ATLAS_EN/html/secondary_characteristics.html]</ref>
** growth of [[body hair]], including [[underarm hair|underarm]] and [[pubic hair]]
** [[vagina]]l and [[uterus|uterine]] growth <ref>[http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html/</ref>
** decreased stature; adult females shorter [[Human height|stature]] than adult males, on average
** widening of [[hip (anatomy)|hip]]s<ref> Hips widen as part of the female pubertal process. [http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html] </ref>; lower [[waist-hip ratio|waist to hip ratio]] than adult males, on average
** increased secretions of oil and sweat glands, often causing acne and body odor <ref>[http://www.hartnell.edu/faculty/asteinhardt/mywebs/sexual_reproduction.htm Sexual reproduction<!-- Bot generated title -->]</ref>
** changed distribution in weight and fat; more [[subcutaneous fat]] and [[fat]] deposits mainly around the [[buttocks]], [[thigh]]s and [[hip (anatomy)|hip]]s
** higher [[digit ratio]], on average{{Fact|date=October 2007}}
==See also==
* [[Puberty]]
* [[Virilization]]
* [[Sex differences in humans]]
* [[Sexual dimorphism]]
== Notes ==
{{reflist}}
=== References ===
"Sexual Maturity." ''Technical Issues in Reproductive Health.'' Columbia University. May 2, 2008. <http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html>.
Steinhardt, A. "Sexual Reproduction." Hartnell College. May 2, 2008. <http://www.hartnell.edu/faculty/asteinhardt/>.
{{Refimprove|date=June 2007}}
* http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html
* http://www.hartnell.edu/faculty/asteinhardt/
[[Category:Secondary sexual characteristics|*]]
[[bg:Вторичен полов белег]]
[[cs:Sekundární pohlavní znaky]]
[[da:Kønskarakteristika]]
[[de:Geschlechtsmerkmal]]
[[es:Caracteres sexuales secundarios]]
[[fr:Caractère sexuel secondaire]]
[[lt:Antriniai lytiniai požymiai]]
[[nl:Secundaire geslachtskenmerken]]
[[ja:第二次性徴]]
[[no:Sekundær kjønnskarakter]]
[[sv:Sekundära könskarakteristika]]
[[zh:第二性徵]]