The breast is the upper ventral region of an animal?s torso, particularly that of mammals, including human beings. The breasts of a female primate?s body contain the mammary glands, which secrete milk used to feed infants. Both men and women develop breasts from the same embryological (embryology) tissues. However, at puberty, female sex hormones, mainly estrogen, promote breast development which does not occur in men. As a result, womens breasts become far more prominent than those of men.