TINA: It was a gloomy day out in the city. The storm clouds were
rolling in, filling up the emptiness that I felt inside.
Empty like the office I was trapped in for months as no one
seemed to need my scientific expertise to solve there.
*knock knock knock*
I heard a sudden knock on the door.
Could it be what I've been longing for this whole time?
CLIENT: Detective Lasisi.
TINA: What brings you in today?
CLIENT: Well, Detective, I'm here to seek the truth. My lady.
My snookums. I thinks she's up to no good. I was given this.
I was told that this is my child. Here's a picture of me and my lady.
And as you can see the detective. She is Black.
I'm Black.
That baby ain't Black. And if it is my baby,
why's his skin color like this?
TINA: This truth you seek is not black and white.
And that's because skin color is not a binary. What we perceive
as skin color is mainly determined by the amount of a
particular pigment produced in our skin—melanin. To
understand this, let's take a deeper look into the skin. Our
skin, the largest organ of our body, is made up of three layers:
the epidermis, dermis, and hypodermis. The top layer of our
skin, the epidermis, is where the magic happens. Well, it's
not magic, it's science, but you get the picture. Right at the
base of the epidermis we find star shaped cells called
melanocytes. Melanocytes are the cells that produce melanin, our
skin pigment. So how is melanin produced? Melanocytes make these
little things called melanosomes. These are little
melanin producing factories that get transferred from the
melanocyte to surrounding keratinocytes. There, the
melanin provides protection from UV radiation and determines the
color of our skin.
CLIENT: Okay, I appreciate you explaining how melanin works and
everything like that. But clearly, I have the melanin
gene. And this baby don't.
TINA: Melanin gene. It reminded me of Billie Jean, who is not my lover.
I stopped there and forced myself to focus
It' not just one gene, there are many. And we all have the genes
for melanin. It's just that we have different variants.
Genes are DNA segments containing information about specific
traits like eye color, height, and blood type. Genes are made
up of molecular building blocks called nucleotides. And the
exact sequence of those nucleotides can vary between
individuals. Different versions of that genetic sequence can be
called genetic variants. When it comes to color, we know quite a
few variants that affect pigmentation, and at least 100
have been identified and studied. Some genetic variants
only affect eye color or hair color. Others affect the entire
melanin synthesis pathway by increasing or decreasing the
total amount of melanin that we produce and changing body-wide
pigmentation. But things are more complicated than just
making more or less melanin because there are two different
types of melanin; the reddish-yellow pheomelanin
particularly evident in people with red hair, and the
brown-black eumelanin, which explains the range of variation
from lightly to darkly pigmented skin. The type of melanin, the
amount of melanin, and the number of melanosomes varies
from person to person and is dependent on our individual
genetic makeup, as well as the environment and our age.
You just got to give him some time. Babies always come out a
little underbaked. It takes time to reach your full adult
pigmentation. I mean, weren't you a little bit lighter when
you were born?
CLIENT: No, I was Black. I've always been Black. Even as a
baby. Trust me. I was there.
TINA: No, but—
CLIENT: No, I understand what you're saying, detective. But
look— Even if this baby gets several shades darker, he's
still gonna be White.
TINA: What do you mean by Black? And what do you mean by White?
CLIENT: I mean, people in Europe are White. People in
Africa are Black.
TINA: Dark skin is not synonymous with African ancestry.
There are populations from some regions in Africa that have skin
that is as light as that of some Europeans. And there are
populations in Asia and Oceania that have skin that is darker
than that of many African populations. Skin color isn't
organized along continental lines. Rather, it maps onto
global distributions of UV radiation. People in various
regions of the world have skin pigmentation that reflects how
their ancestors adapted to their environment. The earliest
hominin ancestors would likely have had light skin underneath
their dark fur. This is the case for our closest living genetic
relatives, Chimpanzees. During the course of human evolution as
our hominin ancestors lost their fur, their skin was the last
barrier between them in the sun. Losing the protective coverage
of our fur meant that our formerly lightly pigmented
ancestors had to evolve skin that was rich in melanin to
protect themselves from UV radiation. But as those early
humans moved into areas with less UV radiation, they faced a
trade off. Melanin limits the amount of radiation that passes
through the epidermis, which is great for protecting our DNA
from UV damage. Reducing the amount of UV radiation that
passes through our skin can have some negative consequences,
specifically relating to the production of vitamin D. Our
bodies can convert a precursor of vitamin D in our skin to its
active form using UV radiation, specifically UVB. There's lots
of evidence that Vitamin D plays a crucial role in immune
function and bone health, among many other things. So as humans
moved through regions of the world with varying UVR
intensities, natural selection played a careful balancing act
of keeping skin melanated enough to protect against the harmful
effects of UVR, while keeping it de-pigmented enough to produce
sufficient vitamin D. When we look at the distribution of skin
pigmentation around the world, we see that there's quite a bit
of variation within the continents. So it doesn't make
sense to equate such large regions of the world to a
particular skin color. We see that there are people across
continents that have similar skin pigmentation, and we see
people within the same continent that have very different skin
pigmentation. An important thing to keep in mind is that this map
describes the distribution of skin color for populations whose
ancestors have remained in this same region for long enough to
be affected by natural selection. What is long enough?
Well, it's hard to say. It depends on a lot of factors,
like how strong the effect of natural selection was, the size
of the population and many other things. Basically, don't expect
your grandchildren to be super adapted to an environment.
Natural selection takes a little bit more time.
CLIENT: Okay, Cool story, bro. Look, the fact of the matter is
Black people make Black babies and White people make White
babies. It's simple.
TINA: Let me ask you this. Do you have any relatives that are
a little bit more light skinned than you?
CLIENT: My nephew's kind of light skinned? But still, my
brother's baby is clearly Black. This baby is not. Look, are you
sure you're an expert? I can go find another detective if you're
not taking me seriously.
TINA: Look, I'm gonna stop you right there. Sir. Let's go back
to the board and I'll explain.
In a complex trait like skin pigmentation. Predicting skin
color based on what the parents look like is not a
straightforward task. Skin pigmentation were simple trait
controlled by a single gene, things will be straightforward.
There could be a genetic variant that makes your cells produce
melanin, and a genetic variant that stops your cells from
producing melanin. In that case, you could have three options for
skin color: no melanin, some melanin and a lot of melanin.
But the thing is, there isn't just one gene affecting skin
pigmentation, there are more than 100. This is because skin
pigmentation is not a simple trait. It's a complex trait. And
because complex traits are affected by many genes, there
are usually many options for what a trait looks like. In the
case of skin color, we see clearly that there aren't just
three options, but dozens of shades in a continuous spectrum
of color.
So putting this all together, it means that you have multiple
genes contributing to skin color, and that you can have
multiple mutations within each of those genes that can lead to
similar effects. We then also have to account for the two
copies of the genes and interactions between genes.
Basically, parental skin color might not be as helpful as you
think.
To think... he said I'm not an expert.
CLIENT: I can see now how skin pigmentation is related to
genetic variation, and all that stuff that rhymes—blah, blah,
blah. How does this tell me if this is my kid or not?
TINA: Oh, it can't tell you that. The genetics of melanin
can explain why you and your sound don't look the same but
can't tell you whether or not you're the father. You need a
paternity test for that which you can get at the store.
CLIENT: What?! I sat through this entire YouTube science explainer
and now you're telling me that you can help me?! I can't believe
this. I haven't even paid you and I want my money back. Ole
wannabe detective...
TINA: As the client thanked me in the background, the emptiness
I felt inside felt a little bit smaller as it was another day
solving another biological mystery.
CLIENT: Three. Shot ABC. Take four.
TINA: Did you know you could probably make butter from human fat
*squirrel giggle*
CLIENT: Even if this is baby gets 20 shades darker it's still
gonna be White.
TINA: It means that you have multiple genes— I'm so sorry
guys. I'm so tiredddd
DIRECTOR: Wanna try that again?
CLIENT: Fake wannabe fifties detective looking— Think you
anthropologist but not really kinda you are but I am not
really either. So you better stop with your Ole wanna—rinkled
coat having
DIRECTOR: OK cut!