Wherever you are right now, take a look around at anyone nearby. If you’re alone, picture some people you’ve seen recently.
Consider how hands, hair, mouthes, eyes, on everyone are all different colors.
Everyone in the world is different. We each enjoy different things, have our own unique quirks, have our own outlook on life and we each bring something slightly different to the world. Two such things are the color of our skin and hair.
Of the people around you or who you’ve seen recently, does any one of them have the EXACT same skin and hair color as you? Maybe they’re totally different or maybe they’re close. But I’ll bet they are not identical. Perhaps their skin is more olive toned, or perhaps they’re fairer, or perhaps darker. Even if you have an identical twin their skin and hair will be slightly different in color to yours.
But why are we all different colors?
Whenever I’ve heard conversations about this, usually someone pipes up that we were all dark-skinned before we migrated out of Africa. As we travelled further north and east, we became whiter. Exactly why this is where folks get a little vague and mumble that it’s something about vitamin D and the brightness of the sun.
The science behind how and why we’re all different is fascinating. Let’s dive right in and you can lay down some knowledge at the next family reunion or games night with friends!
Where We Come From
We’re all African, when you go back to our roots. This awesome infographic from National Geographic shows how we migrated. Across the world we see a clear trend towards those who are further from the equator having lighter skin than those closer to the equator. As climates get warmer, there is a corresponding trend towards darker skin. However there does seem to be a few people that break these rules, such as Alaskan Natives and Aboriginal Canadians. Despite living in very cold and dark areas of the world, their skin color doesn’t cause them to look like a ghost when subjected to flash photography. Let’s explore why but first, let’s go through the basics.
Melanin and Melanocytes – A Quick Recap
For those of you who are regulars at our blog, you may remember two previous articles we had on melanocytes. We looked at the role of melanin and what happens when you have too much or too little. We also looked at the part played by melanin-producing cells, melanocytes, in Parkinson’s Disease, Vitiligo and Waardenburg Syndrome. Let’s do a quick refresher.
Melanin is the pigment that gives our hair, skin and eyes their unique color and protects our body from excessive ultraviolet radiation. Generally speaking, more melanin means darker skin and less means fairer skin. The two types of melanin that produce the color of your hair, skin and eyes are pheomelanin, which adds a pale red/yellow tint, and eumelanin which adds brown. The number and size of melanin particles in your melanin-producing cells, melanocytes, the percentages of the different types of melanin your genes causes your cells to produce and, in light skin tones, the blood’s red hemoglobin and white/blue of our connective tissue all affect our skin color. The presence of fat cells also plays a small role as well as carotene pigment. The resulting combination that is you, or your roommate, or the barista that makes your coffee and this is why we all look so fantastically varied.
Side note: When you tan, your melanocytes have upped their game and are producing more melanin. If you’re the type of person who just burns in the sun, sadly you’ve probably got a defective copy of one of the melanin-associated genes, MC1R, a skin protein that is needed for melanin production.
Why Lighter Skin Evolved
Your mother may have told you at some point that it’s good to get some sun exposure as we need it for vitamin D. The darker your skin, the more exposure you need. But why does darker skin need more sun and how do we get nutrition from light? After all, you may have many skills but being a plant capable of getting your photosynthesis on probably isn’t one of them.
Your mother was correct. Some shortwave ultraviolet radiation, or UVB, is great for you. Your body actually uses light to create vitamin D3 from a precursor in your skin. This is then processed and activated by the liver and kidneys. Harvard health explains how we make vitamin D in more detail if you’re interested. About 90% of our vitamin D is made in this way with the rest coming from our diet, for example fatty fish (mmm, salmon nigiri) and egg yolks.
Even if you’re skin doesn’t crisp in the sun like bacon in a pan, too much UV radiation can actually cause anemia through the breakdown of folate in the body. Low folate is associated with birth defects, poor DNA replication and impaired sperm production. Sheesh!
Conversely low vitamin D levels can lead to weak and brittle bones (rickets disease in children and osteoporosis in adults), concentration issues and fatigue. Our body’s are very particular, huh?!
Producing melanin sounds pretty important then and since it would’ve affected our ability to produce healthy offspring and not die of skin cancer it’s a safe bet that high melanin production would’ve been a survival advantage way back when.
As we migrated to less sunny parts of the world, this advantage would’ve switched to more of a disadvantage. With lower UV radiation levels, less skin pigment meant we got more bang for our buck when we spent time in the sun. Less light plus darker skin meant less vitamin D and poorer health. So paler we became!
Except!
The aforementioned Alaskan Natives and Aboriginal Canadians populations. Despite being way up there on our globe, they remain dark-skinned. Fascinatingly, because the sun reflects off the snow and they eat a ton of vitamin D through fish and mammal blubber, they’ve actually been able to have the advantages of both lighter and darker skin tones. It’s possible that given their short evolutionary history in the north that they may lighten over time but still pretty cool! The part of my brain that loves to bend logic to get its way wonders if my ancestors had had a cheap sushi bar nearby, if I would’ve been able to enjoy more days at the beach today…
Women are Lighter and Men are Darker (really??)
It’s true! Remember how vitamin D levels beings low results in problems with your bones? Vitamin D is important in calcium absorption in the gut. Since women need more calcium during pregnancy and lactation, they need more calcium, more vitamin D and more sunlight! Lighter skins means they absorb more light and again we have a survival advantage. So women across the world are on average 3-4% lighter than their male counterparts.
Humans of the Future
Going forward, with the increase in interracial children, tanner skin will probably become more and more common. With rising UV levels across the world, darker skin will also create a survival advantage although we could counter that pressure with improvements in medicine and technology.
Summary
More radiation means skin evolves to be darker as we’re better protected from said radiation hence less prone to folate loss and skin cancer.
Less radiation means lighter skin is favored as we need less exposure to the sun to get our vitamin D making us less prone to low vitamin D and low calcium absorption.
Here’s to a more adaptive, varied skin toned future!
Further reading:
- Paper on human skin pigmentation as an adaptation to UV radiation by Jablonski and Chaplin
- Ted talk by Jablonski on where Darwin went wrong and using NASA to prove her point
- Paper on the evolution of human skin coloration by Jablonski and Chaplin
