For all women, breasts are a very important and very visible aspect of their "womanhood". It is also probably fair to say that the female breast is regarded by men and women as a key aspect of
The levels of estrogen required to cause breast development are surprisingly low - until stage IV, the growth of the breast in a girl takes place with estrogen levels similar to an adult male. That is why about 40% of male children also initiate "Tanner I" type mammary development during their puberty due to the tendency of their testis to secrete significant quantities of estrogen's in early phases of its development. However, as testosterone secretion increases the breast development ceases and very few boys reach the Tanner II stage.