text: Nature is lazy, just that simple.  It is easier to have the same structure in both men and women (since any such structure has to be written in the DNA, then there is no need for different DNA) and simply have it activated by the few genes that control sex hormones at puberty.\nSuppose that men did not have nipple, then the DNA for NOT having nipple would have to be on the Y chromosome than only men have; and the DNA for describing the nipple would have to be on the X chromosome, but men have ONE X chromosome. The only way to have that would be to have extra code to erase nipples on the Y chromosome, to balance the "have nipple" on the X. uch too complicated.  Mother nature likes things to be simpler.\nSo men walk around with unneeded body parts.