In Humans
Sexual differentiation begins during gestation, when the gonads are formed. 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.
Read more about this topic: Secondary Sex Characteristic
Famous quotes containing the word humans:
“As humans have a prior right to existence over dogs by virtue of being more highly evolved and having a superior consciousness, so women have a prior right to existence over men. The elimination of any male is, therefore, a righteous and good act, an act highly beneficial to women as well as an act of mercy.”
—Valerie Solanas (b. 1940)
“...there is hope for a tree, if it is cut down, that it will sprout again, and that its shoots will not cease. Though its root grows old in the earth, and its stump dies in the ground, yet at the scent of water it will bud and put forth branches like a young plant. But mortals die, and are laid low; humans expire, and where are they?”
—Bible: Hebrew, Job 14:7-10.