In this installment of Science of Sex, we take a look at why genitals look the way they do. Surprise: it’s for reproduction. Keep reading if you want to learn a bit more, however.
Originally I was just going to focus on testicles, which are surprisingly more interesting than I had been lead to believe. However, I couldn’t help myself from going down the rabbit hole and touching on other genitals.
Note: The language in this post is cisnormative because I am focusing on reproduction alone.
Testicles and ovaries are the two types of gonads or reproductive organs; although, the scrotum is more analogous to the labia. Both split down the middle, and the scrotum even has a “seam.”
Anyone who has seen a certain Seinfeld episode is familiar with shrinkage, which occurs when the body is cold, and the genitals retract closer to the body. It’s the cremasteric muscle that’s responsible for pulling in the testicle.
The muscle doesn’t just pull the testicles up and down. Each testicle has its own orbit, so they’ll hang unevenly. Apparently, the right testicle usually hangs higher than the left. Some suggest that this is also a defense mechanism should one testicle become harmed; the other may remain safe. But anatomist Stany Lobo suggests that testicular orbit maximizes space for each testicle, allowing it to remain cool enough.
The current theory is that testicles and the sperm inside them remain slightly cooler than the man’s body by about 3 degrees Celsius (cooler temperatures at night lead to descended scrotums, which may play into why humans so often have sex after dark), but the heat of a woman’s vagina and uterus reactivates the sperm, which are able to survive at those temperatures for the amount of time it would take to fertilize an egg (approximately 50 minutes to 4 hours). Voila!
As best as we can tell, the comparatively-large human penis is designed mostly for pleasure. A larger penis may attract and keep more mates.
The shape of the penis also aids conception. The large, contoured head acts a bit like a shovel as it thrusts into a vagina. This doesn’t necessarily benefit conception by a man’s sperm, but it does displace sperm for any previous partners a woman may have had. A larger corona and more vigorous thrusting can also increase the sperm-displacing effect.
The refractory period prevents a male from re-entering his partner and displacing his own sperm, aiding the continuation of his lineage.
The vagina and uterus are obviously shaped for penile penetration. However, the position of the organs aids reproduction in another way. Before our ancestors walking upright, the uterus tilted to aid “doggy” style sex. When our ancestors did become bipedal, the uterus tilted. One theory posits that to aid face-to-face sex, female lips became more pronounced and darkened in color (mimicking her labia) to attract a mate. I imagine those same characteristics attracted mates to female partners, especially when swollen and darkened due to arousal.
Interestingly, I have yet to come across a lot of information about the shape of the vulva. Perhaps the penis does most of the work when it comes to reproduction. And researchers have yet to come to a conclusion on whether female orgasm aids or hinders conception.
Like the foreskin protects the glans, clitoral foreskin protects the clitoral shaft (which extends deep below the surface). The labia also provide protection for the vagina, which is further protected by the hymen, stretchy tissue around the vaginal opening that can sometimes cover it.
The vagina itself balloons outward during arousal, a process known as vaginal tenting, that makes intercourse easier. The elongation of the vagina reduces penile impact against the cervix, which many women find uncomfortable or painful. No one wants to reproduce if it hurts, after all.
It’s interesting that despite all these adaptations, sex can still be so uncomfortable, especially for women. But perhaps nature’s focus on reproduction is why issues of pleasure, comfort, and connection are so often overlooked.
Further Reading
- Sex At Dawn
- Right–left and the scrotum in Greek sculpture
- The Science of Orgasm
- Why Is the Penis Shaped Like That?: And Other Reflections on Being Human
- Is My Hymen Intact?
- The Still-Misunderstood Shape of the Clitoris
- The Twisted World of Sexual Organs
