5 Facts (Well... Theories) About Why We Have Pubic Hair

(#tbt to 2017 and this post from Tumblr)

What's the deal with pubic hair? Why do other mammals have furry bodies but shorter, finer hair on the pubic region while we have the opposite deal- mostly bare all over with a random bush between the legs? No one knows- evolutionary biologists, gynecologists, dermatologists, sexologists- we don't know. ¯\_(ツ)_/¯ But here are 5 theories:

1. Sexual decoration

Since pubic hair growth only occurs after a surge of androgens and estrogens during adolescence, one evolutionary theory is that pubic hair serves as sexual ornamentation, a neon advertisement if you will, that says “I have reached sexual maturity and efforts to reproduce with me could be fruitful and worth your time and energy expenditure.”

Of course we have no idea which came first- did pubic hair grow at puberty for purposes still unknown, and it became associated with sexuality as a secondary consequence due to it’s timing with sexual maturity, or inversely, did pubic hair grow specifically as a sexual signal once we evolutionarily lost most the rest of our body hair, making the genitals stand out against an otherwise hairless body? Pubes, you inspire more questions than you provide answers!

2. Eyelashes of the genitals

A health function theory is that like eyelashes and nose hair, pubic hair exists to block and sweep away pathogens or other foreign particles from entering a bodily orifice. Sounds logical for vulvas, but I wonder why pubic hair would grow on the pubic bone instead of around the hole at the end of a penis (urinary meatus) if the purpose is to protect the body’s openings?

And is there any evidence that pre-pubescent people or those who remove their pubic hair are getting sick more often because they don’t have pubic hair as a line of defense against pathogens? So many questions!

There was one study that correlated infection of certain STIs with frequent pubic hair removal, but there is no way of knowing if the hair removal caused the increased likelihood of infections. They didn’t ask participants if they were having safe sex or if they were diagnosed with the STI before they started removing the hair or after.

It could also be that the microscopic nicks from shaving creates pathways for infections to enter the body, but that doesn’t help us understand whether pubic hair exists to block disease and if we never grew pubic hair to begin with (vs growing it and then shaving it) would still have increased infection rates.

One thing we do know, research has speculated that trends around pubic hair removal is suspected to be the cause of a decrease in the population of pubic lice. No pubes, no lice, I suppose.

3. Pheromone wafting

Another evolutionary sexual theory is that pubic hair wafts pheromones into the air. Sebaceous gland secretions + dead skin + sweat = a scent that is individually unique and may be consciously or subconsciously sexually attractive to different people.

The idea is that the pubic hair both traps it for the scent to intensify and then wicks it away for potential sexual partners to get a whiff of. But we know less about human pheromones than we do about pubic hair. Gah!      

4. Genital HVAC system

This theory posits that pubic hair serves to regulate the temperature of the genitals, trapping heat and keeping the area warm when needed, and wicking away sweat to keep the area cool when needed. Since like the skull, the skin in the genitals is thinner and blood vessels quite plentiful, there are more opportunities for heat to escape from the body than other parts so hair is needed for insulation. Fair theory, although it begs the question:

•  Why are sweat glands sufficient thermal regulators for the rest of our body, but not the genitals? And I’m no biologist nor am I an expert on thermodynamics, but my understanding of body thermoregulation is that short fine hair is better at absorbing and drawing off sweat for cooling purposes than thick hair, which is why our species lost our fur to begin with, so wouldn’t thick hair be counterproductive?
  
• Again, why is the pubic hair mainly on the pubis? If the idea was to control temperature for reproductive needs, wouldn’t there be more hair on the scrotum (which hang outside the body to keep the testicles at 2 degrees below body temperature anyway) and on the lower abdomen of people with ovaries and uteri? Why does the pubic bone and outer labia require specialized temp regulation when they aren’t involved in reproduction? If the theory is to protect from heat loss due to quantity of blood vessels, wouldn’t the hair grow on the clitoris and penis where blood vessels concentrate?

5. Car bumper of the loins

Whether as a bumper between the genitals and the rocks and dirt our ancestors would sit on, or a bumper between the genitals and someone else’s genitals knocking together during sexual activity, the final evolutionary theory about why we have pubic hair is that pubic hair offers a layer of cushion and protection from abrasion to a very sensitive and vulnerable area.

But then of course one wonders if true, why other primates have thinner, finer hair on their genitals rather then thicker coarser hair. How are they protecting their genitals without pubes? The world may never know…

Which ones do you think are most plausible? Do you have different theory about why humans have pubic hair? Do you have any rebuttals to these theories? Let me know in the comments!