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]]