Male lactation

History

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, 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) as well as Charles Darwin, who commented on it in The Descent of Man, and Selection in Relation to Sex (1871):

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), lesser short-nosed fruit bat (Cynopterus brachyotis), 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. Case reports of lactation induced in transgender women have been published.

References

Citations

Sources

• 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

References

1. [[s:The Descent of Man (Darwin)/Chapter I. Descent of Man, Chapter I]]
2. [[s:Descent of Man/Chapter VI. Descent of Man, Chapter VI]]
3. (2009). "Male lactation: why, why not and is it care?". Trends in Ecology & Evolution.
4. (1999). "Structural and Ultrastructural Study of GH, PRL and SMT Cells in Male Goat by Immunocytochemical Methods". Cells Tissues Organs.
5. (1984). "Galactorrhea in the adolescent". Journal of Adolescent Health.
6. (2018). "Case Report: Induced Lactation in a Transgender Woman". Transgender Health.
7. (2021). "Lactation Induction in a Transgender Woman Wanting to Breastfeed: Case Report". The Journal of Clinical Endocrinology & Metabolism.