Biology Lesson of the Day: Arm Hair

Biology Lesson of the Day

Arm Hair

Adaptation to one's environment and habitat is essential for all creatures, from archaebacteria to humans, viruses to Sequoia trees. Otherwise, changes in those environments or habitats could prove fatal to the creature and spell doom for its species.

Today's Biology Lesson deals with an adaptation that we see in humans: arm hair.

There is no great debate that I am aware of over the origin and necessity of arm hair in human males. In fact, a quick keyword search of "why do guys have arm hair" will bring up mostly results regarding hair removal products, commentary on national and cultural differences regarding shaving, and, for some reason, pictures of Julia Roberts. Still, very little dispute can be found about the purpose of arm hair.

Arm hair is a result of the same stuff that causes other body hair: androgens. In fact, body hair in general is scientifically referred to as "androgenic hair." Androgens are those hormones (including testosterone) typically found in more abundance in males than in females and are, in fact, what stimulate the growth and appearance of all male secondary sex characteristics. A female can also have excess androgens in her system leading to the development of some of these same male characteristics. Contrariwise, a male can have too few androgens and not develop those characteristics.

Now that you understand where arm hair comes from, chemically and biologically, let us now turn to why I believe human males have adapted arm hair.

Picture this: a group of early era males is seated in the cold, shivering against the wind. They have taken care to cover their cores in loincloths (made from the skins of the animal they last killed for food) to block as much of the cold as they can. In an effort to keep their weapon use agile, they have not added sleeves to the loincloth. As a result, their arms are ready but freezing. Some of the men are bigger, hairier. Their bulk and extra covering from the hair keep them warmer for far longer than the smaller, smooth men. If anyone dies from the cold, it will be the latter.

They make their kill and take it home. They prepare it for their families and eat healthily. They feel the grease and other particles of food that stick to their mouths and facial hair. Napkins having not yet been invented, they reach up their forearms and wipe.

This happens year after year, generation after generation. The more hairy of the males outlast the less hairy, both because of protection from the elements and because of having extra food left over on their advantageous arm hair. The ones that outlive the others live to produce offspring likely owning the genes predisposed to growing more hair.

Today, we have sleeves and houses and jobs that typically don't require facing bitter wind to get food. The arm hair seems superfluous. However, we (and I am speaking mainly about males in the first person plural here) have learned to use this adaptation for another purpose. This new purpose is not entirely as necessary for survival against hunger and wind, but it is worthwhile.

This new purpose? Picture this: a guy is out cooking on the grill. He's got his sleeves rolled up (or if he's from Lincoln County, no shirt whatsoever) and the smoke is rolling off the grill. He goes to wipe his brow with a handkerchief? No! He wipes off his brow with his forearm, which is covered with (say it with me) arm hair.

Arm hair, once used to shield man against the elements, is now little more than a napkin. That is why still, to this day, men will always forget to get a napkin when they eat and instead prefer to wipe off their mouths with their forearms. It is just one of the advantages that have carried on through the millennia.