Male and female mammals have mammary glands. Mammary glands will lactate, or release milk, in response to the presence of the pituitary hormone prolactin. Prolactin can be secreted by the brains of both males and females, and acts on mammary glands. In females, prolactin is known to be released by the pituitary in response to a suckling baby.

Before the development of infant formula, wet nurses could be hired to breast-feed a baby for a mother unable to produce milk. From this we know that females can breast-feed even if they were not recently pregnant.

Likewise, some adoptive mothers are able to lactate spontaneously if they manually stimulate their nipples before the adoptive child is turned over to their care.

It seems to make sense that the presence of breast tissue and prolactin would also allow human males to lactate, when a baby is allowed to suckle, which leads to the following:

Like females, human males can spontaneously lactate.

Questions

1. Males who are injected with prolactin or who have pituitary tumors that result in the production of excess prolactin can sometimes lactate. Would this be considered spontaneous lactation?
2. Only one nonhuman male mammal, a fruit bat from Southeast Asia, is known to lactate spontaneously.
Does the fact that more recent male human mammalian ancestors do not lactate spontaneously decrease or increase the likelihood that human males would be able to lactate spontaneously?
3. During in utero development the presence of two X chromosomes sets in motion a series of biological events that help program mammary glands to be able to develop more fully at puberty. Is this likely to happen to males? Why or why not?
4. At puberty, mammary glands begin to develop more fully. Many human males do show signs of breast development during puberty. Is this breast development typically permanent or temporary in adolescent boys?
5. We know that males are able to produce prolactin. If males have less developed breasts than females, do you think they would produce the same amount of prolactin in response to suckling as females?
6. Reflect on your answers to questions 1–5 above and explain why the statement bolded above sounds right, but isn’t.