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.

A sticky situation

For all you Mormons out there who wonder why semen seems so sticky, there is a simple biological explanation. But you may not like it.

Semen from a wide variety of species forms a “plug” that prevents a subsequent sex partner’s sperm from reaching the egg.

Some species form a “hard plug,” while others form a “soft plug.” We humans happen to be of the soft plug variety. Species that form a soft plug have evolved a penis shape that is exquisitely capable of removing a previous male’s soft plug, so that a male’s own sperm can pass this barrier and race toward the egg. Thrusting during sex facilitates soft plug removal. Species that form a hard semen plug generally have a bone in the penis that helps dislodge the previous male’s plug.

This entire scenario reeks of polyandry, when you think about it. Then consider the fact that we are made in God’s image, and that many Mormons believe that God and Joseph Smith are polygynists, and that women do not practice polyandry in the afterlife (i.e. women can be sealed to only one man, while men can be sealed to many women).

Whether resurrected beings have genitals is an entirely different matter, of course. But what does semen biology tell us about humanity in general? What does sticky semen tell us about our creation? Why would God endow men with the ability to so aptly remove a competitor’s sperm, if women were not meant to be polyandrous?