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:
“Because humans are not alone in exhibiting such behavior—bees stockpile royal jelly, birds feather their nests, mice shred paper—it’s possible that a pregnant woman who scrubs her house from floor to ceiling [just before her baby is born] is responding to a biological imperative . . . . Of course there are those who believe that . . . the burst of energy that propels a pregnant woman to clean her house is a perfectly natural response to their mother’s impending visit.”
—Mary Arrigo (20th century)
“The land is the host and humans merely guests.”
—Chinese proverb.