Here's a crazy statistic,
the average man spends more than a month of his life shaving ... his face presumably
But the steampunk 'stache is just one of the many forms of human pelage, or hair and fur,
which mammals use to regulate body temperature,
stay camouflaged, enhance our sense of touch and look fabulous
But if hair is so great, why do we have so little of it compared to even our closest evolutionary ancestors,
why do we even have it at all, and what's going on up here,
as opposed to everything below the up here.
Well you might say SciShow has got you covered.
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All animal hair from the stuff on your head to a porcupine's quills,
to the twitchy whiskers of a mongoose,
is made of the same stuff, the protein keratin,
but humans like other animals have several different kinds of hair,
and they change in surprising ways over time
Fetuses in the womb, for instance, are covered in tiny hairs called lanugo,
when a baby is born these hairs fall out
and fine unpigmented vellus hairs or peach fuzz grow to take their place
Then of course when our awkward teen years roll around we start seeing certain vellus hairs
morph into coarse new growths called terminal androgenic hairs,
these develop in response to growing levels of sex hormones called androgens
Both men and women produce androgens,
but men make a lot more which is why they usually have more body hair
So thankfully all our different kinds of hair don't grow at the same rate,
if they did we'd all look like Afghan Hounds
That's because your hair follicles go through different phases and rates of growth,
turning on and off throughout your lifetime
For example the anagen, or active growing phase of the hair on your head lasts for years
compared to your armpit or nether regions, whose anagen phase lasts just for a few months
Your armpit hair can never grow longer than a couple
of inches because it's growth pattern is limited,
which is nice. You wouldn't want that going down to your knees
So your terminal head hair may be able to reach Rapunzel record book lengths if you never cut it,
but sometimes hair needs a break, so it goes through a resting or telogen phase,
which often results in breaking and shedding
It's these different phases along with things like shaft density and follicle size that make up the
recipe for head hair versus leg hair versus eyebrow hair
Still unless you suffer from the exceedingly rare condition of congenital hypertrichosis
in which the lanugo hair of your childhood continues to grow your
whole life unabated all over your face and body,
humans appear to be practically bare compared to other mammals
But here is a fun fact, we actually have the same number of follicles as our great ape cousins,
about five million individual hairs
It's just that our hair is much shorter and finer than that of apes
Which raises the question, what happened to our fur?
One theory suggests that it started with early hominid shift to bipedalism,
human hair likely started to fade away around 1.7 million years ago,
around the time early human ancestors began living the hot, shadeless African savannah life
and started walking upright, exposing less of their bodies to direct sunlight.
The fact that we still have hairy heads compared to the rest of our bodies
may come from the fact that our domes needed
built-in shelter from the sun more than other parts,
though that does beg the question "why aren't our shoulders hairy?"
Another theory maintains that less hair meant fewer parasites and better health
A super hairy body provides lots of shelter for parasites,
whereas less hair leaves fewer hiding spots for bugs
So bare skin may have been a good advertisement to potential mates for overall health and fitness,
and considering that, of course, everything has an evolutionary purpose,
our head hair to help to protect us from the sun and light body hair to deter bugs,
we may likewise have kept our pubic and underarm hair to help us get it on
Both of these areas house apocrine glands which
release the pheromones that help attract potential mates,
we have extra thick hair in these hot moist areas to help trap and transmit these pheromones
whether we like having it or not.
So next time you pull out your razor take a second to think
about all of the advantages your hair provides you
and that it has been millions of years in the making, and then probably just shave it off
because that's what society demands.
Thanks for watching this episode of SciShow.
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