Stylist: Hey, can I help you?
Tina: Hey, I'm sorry, I'm new here. I'm looking to get my
hair done. Do take walk ins?
Stylist: I don't know if we have anyone who works with,
uh, textured hair.
Tina: Textured hair?
Stylist: You know what— I have so many friends that have
curly hair, I could probably, I could probably do your hair.
Just go and sit down and I will be with you in just a
second.
Client: Oh my god, I love your hair. It's so poofy.
Can I touch it?
Tina: You're probably wondering how I ended up in
this situation. We'll talk about that later. But first,
let's talk about why we even have scalp hair in the first place.
And why does it look like this, this, this, and this?
If you think about it, it's pretty weird, right? Humans
stand out from other primates with their naked bodies. But
for some reason, one of the places that we still have hair
is the top of our heads.
Well, looking at our species, we typically have a full head
of hair as adults. Sorry to all you bald-headed baddies
out there. It may seem weird that humans went for this non
committal mix between being naked and being furry. But it
makes a little bit more sense if you consider it in the
broader context of human evolution. Humans most likely
lost their body hair to evolve an impressive thermoregulatory
system based on sweat. This system relies on evaporative
cooling, which happens when sweat evaporates directly from
our skin. So you might wonder why not be completely naked
then? Wouldn't it be important to cooler heads too? Well, it
might have something to do with protecting our really
sensitive brains. As animals that walk up right, our heads
get the brunt of the solar radiation that comes down on
us. Brains generate a lot of heat and are very sensitive to
overheating. So waiting for our heads to overheat and then
activating a sweat response might not be a great strategy.
Instead, a better option would be to use a barrier that
reduces the effect of heat gain from solar radiation.
That's why most mammals living in the desert and other places
with lots of solar radiation still have fur. Fur actually
blocks a lot of the radiation from reaching the skin but it
becomes an insulating trade off. You block heat from
reaching the skin but also limit the heat that can
escape. Enter curly hair. The tightly curled hair that we
see in many human populations has this incredible structure
that leaves lots of air pockets between hair strands
and maximizes the distance between the top of the hair
and the scalp. This makes it a great solution to minimize
heat gain from solar radiation while maximizing the amount of
heat that can be lost from the scalp. In other words,
curls keep you cooler in the sun.
Client: Oh my god, your hair is so different.
Tina: Okay? Obviously not all humans have the same hair. So
why is our hair so different?
The answer is evolution. If the last common ancestor of
all modern humans had tightly curled hair because of some
thermo regulatory advantage, it means that natural
selection had some effect. A quick recap on natural
selection. It's the process through which populations of
living organisms can adapt and change. But even when natural
selection crafts a super handy trait it may not stick around
if the pressure to have that trait is no longer around. So
as humans migrated into all kinds of different climates,
there may no longer have been an advantage to having tightly
curled hair. There are a number of plausible scenarios
for what happened next: Option one, neutral evolution or
genetic drift, the genes affecting hair no longer
experience selection. So in each generation, the genetic
variants associated with decreasing hair curl were just
still likely to be passed on as those variants that
increased hair curl. Option to selection in the opposite
direction. If tightly curled hair increases heat loss,
there may have been cases where it would have been more
favorable to retain heat. So for populations who were in
particularly cold environments, we might
consider that there was some advantage to having straight
hair. Option three, the selection of traits that are
genetically linked to hair. The thing about our genome is
that there isn't a one to one relationship between traits
and genes. Many traits are influenced by multiple genes,
and many genes influence multiple traits. That means
that in some cases, we're not really sure what the target of
selection was. To learn more about this, make sure to check
out our previous episode on skin pigmentation. For
example, looking at the Ectodysplasin A Receptor Gene
(EDAR), we see evidence of selection in East Asian
populations. The variant that was selected makes hair
thicker and straighter, which might make you think that
natural selection favored that kind of hair, but this variant
also has an effect on the shape of your teeth and
mammary glands, among other things. So the reason that
thicker straighter hair might be more common in those
populations could be because of a seemingly completely
unrelated trait. To sum this all up, because different
populations have different evolutionary histories, we see
a lot of variation in hair around the world.
Client: Just like a little sheep, I love woolly hair.
Stylist: Excuse her. It's not woolly. She actually has a 3C
4A curl pattern.
Client: ABC 123, whatever. I love afros.
Tina: We talk about hair and subjective categories like
straight, wavy, curly, or we try to come up with
classification systems like type four, type three, but
hair doesn't exist in multiple discrete categories. What we
know is hair texture, hair shape, or hair morphology is
actually continuous variation. Looking at an individual hair
strand, we can distinguish two aspects of its shape, cross
section, and curvature. If you take a hair, cut it in half
and look at the surface, you can see its cross-sectional shape
and size. People often talk about fine and coarse hair,
but what they really describe is variation in the cross
sectional size of a hair fiber. Also, not all hair
strands are perfect circles hair can be circular oval,
sometimes cross sections can look weirdly triangular, or
even kidney-shaped. But the type of hair variation that we
most often refer to is curvature. The range of
variation from straight to tightly curled hair is a
consequence of the curvature of individual hair strands.
That's not to say that there's no place for describing hair
textures using a typing system. One of the most widely
used hair typing systems is the Andre Walker system. Black
women in the natural hair movement have adopted this
framework and developed it even further to give language
to the huge range of variation in our hair because science
didn't bother to do that. Until we have widely available
tools to easily measure our hair curl objectively, it's
reasonable to use the best descriptive language that we
have, even if it's a bit subjective.
Client: So what are you looking to do with your hair?
Tina: Well, I'm I'm hosting this new science show and I'm
trying to figure out my look, I'm not really sure what I
want, but I'm open to suggestions.
Stylist: So do you maybe want something like the Rachel, or
Ariana Grande, or maybe even Taylor Swift with bangs?
Tina: Are you sure you know how to work with my hair?
Stylist: Oh yeah, absolutely. And now that I take a closer
look, it doesn't even look that frizzy. You're so lucky
that you have good hair.
[slow-mo] Good Hair
Tina: What's a scam that's become so normalized, we don't even
realize it's a scam anymore? Good hair versus bad hair.
The idea of good versus bad hair is so insidious that it's
normalized the expectation to take drastic measures to alter
your hair texture, if it doesn't fit biased standards
of beauty, even if it causes severe consequences to your
health. Discrimination against certain hair textures affects
everything from mental health to whether people are
perceived as professional in the workplace. We've even had
to put policies in place to protect people's rights to
wear their hair, the way it grows out of their scalp. But
did you know that this runs so deep that it bleeds through
into the scientific literature. One example is
this "real" medical condition called "woolly hair syndrome,"
where the "disease" is defined as strong coiled hair in
"non-Black people." There is a very long history of people
trying to present their biased opinions as scientific fact.
Especially in terms of presenting some people as
inherently better than others. If we ask people around the
world what they consider to be beautiful hair, we'd see that
there are many different opinions hair might have
evolved for a very functional reason like protecting our
heads from solar radiation, but we now use it as a medium
for expressing our identities and creativity.
Sometimes, that means finding someone who knows how you want
to express your identity.
Braider: so what do you think?
Tina: I love it.
Braider: Now tell me what you learned.
Tina: Always read the reviews online
Braider: Please do.
Tina: Sometimes cross sections can lurk. *chuckles* Can lurk. *Snort*
Everything is going so well.