The Descent of Man, and Selection in Relation to Sex
Male lactation was of some interest to Alexander von Humboldt, who reports in "Voyage aux régions équinoxiales du Nouveau Continent" of a citizen of the village 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):