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.
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.
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.
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.
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.
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.
I said to 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.
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!