Men have nipples due to how human beings develop in the womb. Both men and women start developing similarly in the early stages of fetal life, before sex chromosomes influence differentiation. The nipples form before the sex of the fetus is determined. Once the Y chromosome comes into play for males, it alters development, but the nipples have already been formed and they just stay in place. Although male nipples do not serve a physiological function like female nipples do for breastfeeding, they remain as a byproduct of our developmental origins.