On the origin of nipples

Did you ever see a kid with extra (supernumary) nipples in gym class? I did. In fact, my sister has supernumary nipples. We humans have genes that encode an entire row of nipples (like a dog or a cat). However, these genes are normally suppressed in humans, although they’re still in our DNA. Extra nipples tend to run in families, and occasionally a person has a spontaneous mutation that causes one of these nipples to arise from our evolutionary past, which brings me to my next question:

Why do men have nipples? Nipples arose quite recently (evolutionarily speaking), and in some mammalian species, males actually nurse their young. Nipples first appear at around day 30 of embryonic development, before a fetus is visibly male or female. Male nipples are vestigial (they usually don’t produce milk). However, both men and women are endowed with all the necessary machinery to nurse a baby. If you give a man the right hormones, he can nurse too.

Occasionally a human being is born with testicles and a vagina–with an X and a Y chromosome, but no uterus or ovaries. These “women” have androgen insensitivity. If you have a mutation that prevents a response to testosterone, you become a woman by default, even with testicles. These women are entirely capable of nursing children.

Women who have never had children can also induce lactation if they mechanically manipulate their nipples enough. I’ve even seen a male or two who managed this trick.

So why did God give men nipples? I really have no idea. I welcome any thoughts. Does it have something to do with sex? Maybe it has more to do with garment markings.