The Causes of Hair Growth

Hair is a tricky one. I hypothesize that there are three causes to hair growth and all three are in play simultaneously. Fact: hair grows at more areas of the face and body on men than on women. This would still be true if we lived in a society where women did not shave their shins, forearms, armpits, etc.  Based on this fact, one can reasonably conclude that it is either testosterone or the lack of estrogen that is responsible for hair on certain parts of the body (e.g. center of the chest, upper lip, etc.). A very popular belief today is that the more facial/body hair a man has, the more masculine he is (and the more testosterone he has). Based on this, one could deduce that, out of all races, Asian men must be the least masculine (and have the lowest amount of testosterone).

Table of total plasma testosterone by ethnic group using data from over 150 peer-reviewed medical journal articles.

This table shows that East Asians actually have very high average total plasma testosterone (5,673 ρg/mL). The popular belief that Asian men have low testosterone is actually not supported by any evidence. Furthermore, looking at the table, there is no correlation between testosterone level and hairiness. So what causes hair?

I hypothesize three causes—all in play simultaneously:

1.       Hair grows at areas that “expect” to encounter friction. (This is genetically inherited.)

This is partly based on armpit and groin hair. Humans have been walking for hundreds of thousands of years and the genes we inherit today still expect us to do so. When walking, the legs move to and fro which creates friction between the thighs and the genitals. Furthermore, the arms sway to and fro and encounter friction with the torso. Patches of hair grow preemptively at these areas. Less obvious than these are the eyelashes, which are the result of friction between the upper and lower eyelids upon blinking.

“Expected” friction is also how I explain scalp hair and eyebrows. Imagine a life in the rough outdoors, like a forest, as humans have lived for thousands of years. We would be brushing our heads against foliage from time to time. And any time we lay down and roll around, the head would encounter friction. As a result of thousands of years of evolution, we’ve developed scalp hair. Today, though, in our sheltered lifestyles, the head is no longer brushing against many things. Head hair still grows as a vestigial structure, though.

Why isn’t the entire head simply covered in hair? Because only the top half of the head encounters friction. Imagine a 3D oval, similar to an egg, with a pivot point attached at the bottom. Imagine that it is sitting under those car wash cleaning curtains. Imagine that it is leaning/tilting in every direction possible:

The bottom half of the ovoid would remain untouched, due to the position of the pivot. This is why hair only develops on the top half of the human head. A more realistic example would be a (cave) man reaching for a berry deep in a bush. He needs to stick his head in the bush to see and reach the berry. No matter what direction he tilts his head, pivoting about the neck, only the top half of the head will encounter friction with twigs and leaves.

So why doesn’t the forehead have hair? Because the human head doesn’t have radial symmetry like an egg; there is a brow ridge which protrudes beyond the forehead:

Typical man’s head

Brow ridge protrusion

Thus, it is the brow ridge, rather than the forehead, that is expected to encounter friction with foreign objects. The result is human eyebrows. Today, though, our faces hardly brush against things. I can only think of three instances: putting on or taking off a shirt; using a towel to dry the face; and hairstyles with long bangs. Eyebrows are considered by many to be vestigial structures.

 

2.       Hair grows at areas that frequently encounter friction. (This is up to free will, a.k.a. nurtured.) This is amplified by testosterone.

This second cause is based areas that frequently encounter friction thanks to modern society. From the perspective of humankind these areas are new. For instance, men develop nipple hair because the nipples chafe against shirts—a modern invention. It is the nipples that develop hair because, relative to the rest of the torso, the nipples stick out the most and thus encounter the most friction. Similarly, frequently brushing the side of the cheeks against a popped collar will induce hairs to grow on the side of the cheeks. Wiping your butt with toilet paper is frequent friction that will eventually lead to the growth of butt crack hairs. Some people have hair on their big toes. This comes from friction between the big toe and the strap of sandals or the toe box of (loose) shoes.

If testosterone level is high, the likelihood of hair growth from friction will be greater. For example, a man may have to brush his cheek against along a popped collar 100 times for one hair to grow, whereas a woman may have to do it 1,000 times for the same effect.

 

3.       Hair grows from underused muscles. This is greatly amplified by testosterone.

If you are an adult female and underuse just about any muscle of the face or body, then fat, a.k.a. adipose tissue, will result. For adult males, fat and hair will result. When I say “underuse” I mean “not using a muscle near its max potential.” The relationship between body hair and testosterone is already well-known, hence the alternative term for body hair: androgenic (male hormone) hair. The “muscle underuse” part is based on my observation of thousands and thousands of male faces and bodies. Why do some men have chest hair, forearm hair, or a full beard, while other men do not? A large part of this is simply genetic; some races are nearly hairless while others are almost completely covered in hair. I believe the non-genetic part (i.e. the nurture/environment part) is muscle use. I’ve observed a very strong correlation between body fat and body hair. For every instance of body hair, directly underneath the hair was fat (from muscle underuse). Likewise, for every instance of no body hair, there was visible muscle definition and a lack of fat.

Pictured above is what citizens of the internet like to call a “neckbeard”—an insulting term for a fat, lazy, basement-dwelling nerd. I believe the internet is close to my hypothesis for stereotyping fat, lazy men as having excess facial hair around the jaw and neck area. I hypothesize that if someone frequently or intensely used a muscle then hair would cease to grow atop that muscle and atop the tendons attached to the muscle. In the case of the full beard, the muscle is the masseter, which is responsible for biting, chewing, and closing the jaw. Underuse of the masseter muscle results in hair atop the masseter and the immediate surrounding area. Frequent and intense masseter usage makes the lower corners of the face low in fat, muscular, and nearly hairless, like this guy’s:

Now, you’re probably thinking, “No, this can’t be. Muscular men are just shaving their body to show off their muscle definition.” After observing thousands and thousands of photos, I really do not think this is the case. Hair simply does not grow on the side of the jaw and neck due to developed masseter muscles, as I’ve concluded. I have seen a handful of photos that seem to break the rule by showing dense hair growing on top of low-fat, defined muscle, but I actually believe these are the work of hair transplant surgery or bathing in minoxidil.

Here’s an example of hair that resulted from underused masseter, chest, and abdominal muscles (fat). If he used or worked out these muscles with higher frequency then hair would become very scarce at these areas. In the bodybuilding community, a body with big muscles and body fat is known as “bear mode” because of the resemblance to a bear in size and hairiness. There is a very strong correlation between fat (from muscle underuse) and body hair.

The largest groups of tendons are the fingers and toes. There are no muscles in the fingers—just tendons. Tendons alone are useless, though, and must be attached to muscles to be pulled. This is why tendons run through the fingers, hand, and wrist to the forearm, where they are pulled by the extensor and flexor muscles:

The function of the extensor muscles is to extend the fingers and dorsiflexion of the wrist. Underuse of these muscles results in hair on top of the forearm. Frequent and intense use of the extensors results in little to no hair atop the forearm. I believe most bodybuilders truly have hairless forearms from handling dumbbells often—not because they shave their forearms to show muscle definition.

I have yet another hypothesis that says men favor using muscles while women favor using tendons, ligaments, and cartilage (i.e. the joints). I talk about this in “The Fundamental Difference between Men and Women, Part 2: Face and Body”. I believe men in their natural state would greatly underuse their fingers and wrists, thus underuse the forearm muscles, and thus develop forearm hair. I believe women in their natural state would frequently use their fingers and wrists and thus not develop forearm hair.

Most people today underuse the forelimb muscles in the legs. Today, we seldom lift our toes upward and flex our ankles upward. This is known as dorsiflexion, and the muscles responsible for this are located in the shins. Just like the muscle-tendon-finger system in the arms, underuse of these shin muscles causes hair to grow on shins. I believe this is the natural state for men. If a person frequently lifts their toes and ankles upward, they would not have shin hair. I hypothesize this may be the natural state for women.

There are some muscles of the body that the majority of men underuse. These muscles are the orbicularis oris (upper and lower lip), mentalis, digastric, and mylohyoid muscles, and the result of their underuse is a moustache and a goatee.

Why these particular muscles? These muscles control movements of the lips and tongue—the organs responsible for speech. As you probably know, men speak far less often than women (i.e. frequency), which results in underused muscles. The orbicularis oris controls lip movements. The mentalis is also known as the pouting muscle. The digastric muscle controls tongue movements. The mylohyoid muscle is responsible for high-pitched speech and singing. If, in addition to these muscles, the masseter muscle is underused, then the man would have a full beard. Not all men underuse the masseter though. I believe about 90% of Asian men heavily use the masseter muscles and are thus “incapable” of growing a full beard—just a goatee.

In the torso, there are two areas of muscle that all men seem to underuse. To be honest, I’m not exactly sure how these areas would be used. One is the sternum at the center of the chest, which is made of cartilage. Underuse produces hair at the center of the chest. For some men, the hair spreads across the whole chest. I hypothesize that these men are not using their chest muscles to the fullest and that there is also a layer of fat beneath the hair. The other area is the lower abdomen (above the groin).




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