Everything about Secondary Sex Characteristics totally explained
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:
Female
Further Information
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