It is possible, and has been observed in animals and humans. In 1992, 18 Dayak fruit bats were captured from a rainforest in the Krau Game Reserve, Pahang, Malaysia. Of the 10 mature males captured, each had functional mammary glands from which small amounts of milk were expressed. A breast is a breast. Male lactation is physiologically possible and, according to Dr. Robert Greenblatt, production in males can be stimulated by letting a baby suckle for several weeks. Indeed some human males secrete milk at birth and at puberty.Historically, male lactation was noted by the German explorer Alexander Freiherr von Humboldt prior to 1859, who wrote of a 32-year-old man who breastfed his child for five months. It was also observed in a 55-year-old Baltimore man who had been the wetnurse of the children of his mistress.
_"Male Lactation" by Professor Patty Stuart Macadam of the Department of Anthropology at the University of Toronto (Compleat Mother, Fall, 1996, Volume 43).