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Q: Why do men have nipples? Is it true that the father of a motherless child can sometimes nurse the baby?

A: Human embryos are female at conception and become male only when exposed to hormones produced by genes on the Y chromosome. But because the basic blueprint was female, males retain some remnant structures of the female, such as the breasts.

In women, production of estrogen and progesterone at puberty and during pregnancy stimulate the breasts to grow and develop the structures required to produce and secrete milk. These structures do not form in males. Even though some diseases can cause male breasts to become enlarged and even secrete a small amount of milk-like substance, they cannot produce enough to feed an infant.