Not necessarily. Occasionally, male mammals feed their young — including some human men.
The Men Who Lactated
In 2002, news reports described a 38-year-old Sri Lankan man who, after his wife died in childbirth, fed his two infant daughters with his own milk. In 1981, a study documented a 27-year-old man with galactorrhea related to hyperprolactinemia; his breast secretion contained lactose, alpha-lactalbumin, and lactoferrin, at concentrations within the ranges of normal human colostrum and milk.
Reports of men nursing babies go back to the nineteenth century — and, if you like, to myth. Even men without pituitary tumors can produce milk: after their nipples are repeatedly stimulated by a nursing infant, their prolactin and oxytocin levels rise, and at least some individuals can begin producing milk after a while.
Other mammals do it too. Male Dayak fruit bats secrete small amounts of milk, though actual nursing by males has not been observed; their mammary development fluctuates seasonally, leaving open the possibility of auxiliary nursing. And males of many more species can lactate under stress, castration, or pituitary tumors — including the famous 2015 Indian male goat that lactated.
Why Did Male Nipples Survive Evolution?
Here is the puzzle: the genes and regulatory sequences for mammary glands exist in the genome of every normal mammal. The cells that will form the breasts are positioned before the embryo's sex is even determined. Darwin himself wondered why male nipples had not simply regressed, and cautiously suggested that there may have been a time when both sexes could nurse.
Modern biology offers an answer: carrying the breast structures without hormonal activation does not interfere with hunting, defending, or mating. There is no ecological pressure pushing males to lose them. And male nipples are not purely vestigial — they still have physiological function. Nipple stimulation causes or enhances sexual arousal in about 51.7% of men.
The Economics of Who Nurses
Females are simply more efficient at the job. During lactation, a human mother uses about 85 kcal of her food energy to produce 100 ml of milk; the infant absorbs about 70 kcal from it — a conversion of roughly 82.4%. Males can share the workload indirectly, by bringing food to the nursing female. There has never been strong selection for males to nurse directly with their bodies.
The evolutionary logic is blunt: a male can pass on more genes by mating with more females than by nursing the offspring of one. Among mammals, males directly care for offspring in fewer than 10% of species, and far fewer actually attempt lactation. Biological traits are often redundant — kept because they cost nothing to carry.
Hormones, Medicine, and the Male Breast
During puberty, testosterone blocks breast tissue expansion in boys. When hormones go wrong, male breasts can grow — a condition called gynecomastia that can cause distress and discrimination. Testicular failure, prolactin-secreting pituitary tumors, and cirrhosis-related hormone imbalances can enlarge male breasts and produce nipple discharge. Men recovering from long-term malnutrition may leak milk due to endocrine disruption. Men can also develop breast cancer.
Certain drugs cause nipple discharge as a side effect — anabolic steroids, for example, and antipsychotics like chlorpromazine. And because of maternal hormones crossing the placenta, newborns of either sex sometimes have nipple discharge.
Today, fewer than ten thousand 46, XY individuals worldwide attempt to breastfeed each year, including some transgender women. Men with benign pituitary tumors can produce more milk than the average woman. Inducing lactation with prolactin in men carries risks of other endocrine and psychological problems — though some men accept them. Transgender women nursing under medical support have accumulated reports with no indication that their usual hormones harm infants.
The Deeper Origin: Skin Glands, Not Fate
The mammalian breast is itself a specialized skin gland — closely related to the apocrine sweat glands, which produce the oily, protein-rich sweat of the armpits and groin. Add water, minerals, immune components, and lactose, and you essentially have milk.
