All humans are equipped with mammary glands. Females just happen to be more developed in order to protect the glands with extra fat and breast tissue. Male breasts a smaller due to the natural selection of only needing 1 parent to breast feed a child so lactation is triggered with hormones after pregnancy.. But there have been case of male humans spontaneously lactating to feed a child when the mother passes away unexpectedly. Female humans are also able to induce lactation with hormones even when never getting pregnant.