Production of milk (lactation) from a male mammal's mammary glands is well-documented in the Dayak fruit bat and the Bismarck masked flying fox. The term "male lactation" is not used in human medicine. It has been used in popular literature, such as Louise Erdrich's The Antelope Wife, to describe the phenomenon of male galactorrhea, which is a human condition unrelated to childbirth or nursing. Newborn babies of both sexes can occasionally produce milk. This is called neonatal milk (also as "witch's milk") and not considered male lactation.
Male lactation was of some interest to Alexander von Humboldt, who reports in Voyage aux régions équinoxiales du Nouveau Continent about a citizen of the Venezuelan village of Arenas (close to Cumana) who allegedly nurtured his son for three months when his wife was ill, as well as Charles Darwin, who commented on it in The Descent of Man, and Selection in Relation to Sex (1871):
It is well known that in the males of all mammals, including man, rudimentary mammae exist. These in several instances have become well developed, and have yielded a copious supply of milk. Their essential identity in the two sexes is likewise shown by their occasional sympathetic enlargement in both during an attack of the measles.
Darwin later considered the nearly perfect function of male nipples in contrast to greatly reduced structures such as the vesicula prostatica, speculating that both sexes may have nursed young in early mammalian ancestors, and subsequently mammals evolved to inactivate them in males at an early age.
Evolution and biology
Male mammals of many species have been observed to lactate under unusual or pathogenic conditions, such as extreme stress, castration, and exposure to phytoestrogens, or pituitary tumors. Therefore, it is hypothesized that while most male mammals could easily develop the ability to lactate, there is no selective advantage to male lactation. While male mammals could, in theory, improve their offspring's survival rate through the additional nourishment provided by lactation, most have developed other strategies to increase the number of surviving offspring, such as mating with additional partners. Presently, very few species are known where male lactation occurs and it is not well understood what evolutionary factors control the development of this trait.
Nonhuman animal male lactation
The phenomenon of male lactation occurs in some species, notably the Dayak fruit bat (Dyacopterus spadiceus) and the Bismarck masked flying fox (Pteropus capistratus). Lactating males may assist in the nursing of their infants. In addition, male goats are known to lactate on occasion.
Human male lactation
Spontaneous production of milk not associated with childbirth, known as galactorrhea, can occur in human males and females. Two case reports of lactation induced in transgender women have been published.
- LGBT Reproduction
- Milking the bull, a proverb that refers to the act of milking a male animal
- Male egg
- Male pregnancy
- Voyage de Humboldt et Bonpland; 1-3. Voyage aux régions équinoxiales du Nouveau Continent : fait en 1799, 1800, 1801, 1803 et 1804. Tome 1 / par Al. de Humboldt et A. Bonpland; rédigé par Al. de Humboldt; J. Smith (Paris), 1814-1825, p. 376, (Online at gallica)
- Descent of Man, Chapter I
- Descent of Man, Chapter VI
- Kunz, T; Hosken, D (2009). "Male lactation: why, why not and is it care?". Trends in Ecology & Evolution. 24 (2): 80–85. doi:10.1016/j.tree.2008.09.009. PMID 19100649.
- Gómez MA, Garcés-Abadías B, Muñoz A, Vásquez F, Serrano J, Bernabé A (1999). "Structural and Ultrastructural Study of GH, PRL and SMT Cells in Male Goat by Immunocytochemical Methods". Cells Tissues Organs. 165 (1): 22–29. doi:10.1159/000016670. PMID 10460970. S2CID 31237459.
- Rohn, R. D. (1984). "Galactorrhea in the adolescent". Journal of Adolescent Health. 5 (1): 37–49. doi:10.1016/s0197-0070(84)80244-2. PMID 6420385.
- Reisman, T; Goldstein, Z (2018). "Case Report: Induced Lactation in a Transgender Woman". Transgender Health. 3 (1): 24–26. doi:10.1089/trgh.2017.0044. PMC 5779241. PMID 29372185.
- Wamboldt, R; Shuster, S; Bikrampal, B. S. (2021). "Lactation Induction in a Transgender Woman Wanting to Breastfeed: Case Report". The Journal of Clinical Endocrinology & Metabolism. 106 (5): e2047–e2052. doi:10.1210/clinem/dgaa976. PMID 33513241. S2CID 231755160.
- Angier, Natalie (February 24, 1994). "Some Male Bats May Double as Wet Nurses". The New York Times. Retrieved December 3, 2013.
- Cr. J. Covey, Francis, Charles M., et al.; "Lactation in Male Fruit Bats," Nature, 367:691, 1994.
- Fackelmann, K.A.; Science News, 145:148, 1994.
- Anomalies and Curiosities of Medicine G.M. Gould and W.L. Pyles