Why do males have nipples?

Nearly all mammals have nipples, which females use to feed their offspring. The genes of mammals code for nipple development in the fetus, regardless of sex. In fact, the default body plan is female, and in the absence of male hormones such us testosterone, every mammalian fetus will develop an essentially female body.

Despite the uselessness of male nipples, they haven’t disappeared because natural selection acts only on features that affect survival. Male nipples remain as vestigal features, like the human appendix.