This episode is supported by Curiosity Stream.
The story of our hair, our hair-story if you will, is pretty tangled. Scientists are still
straightening out the facts, combing through questions, cutting to the root of this biological
tale. We mustache: What’s the deal with hair?
And don’t worry. I know you’re about to dye. We’re cutting… the puns. Starting now.
[OPEN]
Hair is a big part of our culture – it’s hit broadway, whipped back and forth, even
spawned its own musical genre – and made this possible. Impressive Kyle.
But W the actual eff is it? Hair is made of keratin, the same protein that forms your
fingernails… with a few extra ingredients.
It gets its color from two types of melanin: brown-black eumelanin and red-yellow pheomelanin.
These pigments are produced down in the hair follicle, and whether each strand comes out
curly or straight depends on the angle of the follicle itself. Your DNA combination
dictates whether you turn out to be a Thor, a Loki, or … maybe a Weasley.
Blondes might have more fun, but they don’t have a lot of pigment. They have a mix of
the two hues, but at low levels. Eumelanin dominates brunette heads. But redheads have
mostly reddish pheomelanin.
This pigment ratio is controlled by a gene, which also controls the melanin in our skin.
In Africa, that pigment gene doesn’t really vary – and that makes sense. You need a
lot of eumelanin to absorb UV rays. But the farther we journey from our tropical origins,
the more variation we see. As we started branching out into shadier climates, skin diversified,
and so did hair.Ancient DNA tells us that even some Neanderthals had red-headed changes
in their MC1R genes as they adapted to Northern living.
So why does our hair grow where it grows? And, not grow where it doesn’t. We actually
have about the same number of hair follicles as our ape ancestors, and some hair grows
almost everywhere – but ours is only thick and luscious in a few spots. Unless you’re
Kramer.
One idea is that we ditched our fur to keep cool. Running across the savannahs is a hot
way to live, and bare, sweaty skin sheds more heat.
Real talk: Hair makes good habitat for parasites. And some of those habitats are in the Southern
Hemisphere… if you know what I’m saying. The creatures that wander our follicular forests
might tell us when our ancestors started showing skin.
Three kinds of louse can live on Homo sapiens, and each occupies a different niche: [head
lice, body lice and pubic lice]. Headlice have been with us the longest – maybe since
we split from chimps. The pubic lice story is … it’s weird. They’re more closely
related to gorilla lice, and showed up more recently. We probably got them from sharing
gorilla nests… with each other, not with gorillas. Or from butchering bushmeat. Those
lice never journeyed up, that means our body hair had already started to disappear, stranding
those lice on their southern raft, around 3 million years ago.
Body lice, despite their name, live in clothing. They only joined our party 42,000-72,000 years
ago– which could be when we switched our fig leaves for leather jackets.
Speaking of undergrowth, why does downstairs hair feel coarse and wiry – same as facial
hair and armpit hair. That’s because those hair islands burst forth like hormonal volcanoes
from a sea of adolescence.
“Androgenic” hair is triggered by the production of sex hormones during puberty.
Men have more of this hair, because they produce more androgens. It also tends to have more
of the brown-black melanin pigment than head hair, which is why the carpet doesn’t always
match the drapes. Hair near our underarms and genitals also helps trap and project odors
and pheromones we start secreting at puberty.
As we get even older, the pigment-producing cells in our follicles retire – and while
our hair continues to grow, it comes in pigment free. Grey hair isn’t a color, it’s a
lack of color.
Normally we lose 40 or 50 of those hairs per day, that’s fine because we grow as many
new ones. But when the hair follicle stem cells go quiet – like from aging – or
are destroyed – like what happens in many chemo therapies – that’s hair loss. But
I wouldn’t know anything about that. It’s all real baby.
Of course, if you’re losing your hair, don’t worry, I’m sure science will figure something
out. Besides, it’s a classic trend we’ve been rocking for millions of years.
Stay curious.