Asian Girl With Full Breasts

Breastfeeding
The primary function of mammary glands is to nurture young by producing breast milk. The production of milk is called lactation. (While the mammary glands that produce milk are present in the male, they normally remain undeveloped.) The orb-like shape of breasts may help limit heat loss, as a fairly high temperature is required for the production of milk. Alternatively, one theory states that the shape of the human breast evolved in order to prevent infants from suffocating while feeding. Since human infants have a small jaw (not protruding, like other primates), the infant's nose might be blocked if the mother's chest was too flat. According to this theory, as the human jaw receded, the breasts became larger to compensate.
Milk production unrelated to pregnancy can also occur. This condition, called galactorrhea, may be an adverse effect of some medicinal drugs (such as some antipsychotic medications), extreme physical stress or endocrine disorders. If it occurs in men it is called male lactation, and is often classified as a pathological symptom due to its strong correlation to pituitary disorders. Newborn babies are often capable of lactation because they receive the hormones prolactin and oxytocin via the mother's bloodstream, filtered through the placenta. This neonatal liquid is known colloquially as witch's milk.