The skin we’re in

Skin color, it turns out, is little more than adaptation in action

The skin we're in
After all, it's only skin... [Image credit: Emma Bryce]
By | Posted February 19, 2012
Posted in: Life Science
Tags: , , ,

So here’s a thought: How did different skin colors evolve? Evolutionary biologist Nina Jablonski wrote the most widely accepted theory in 2000, saying that it comes down to a practical combination of three things: skin, ultraviolet light and vitamins.

It started with skin…

The story begins in Africa, about two million years ago, when early members of the genus Homo began moving from the cool cover of forests onto sunnier open plains to find food. These early humans were densely covered in hair, which increased their body temperatures and made them slower hunters.

Thanks to genetic variation, some were born with less hair. Since those less-hairy hominids had a survival advantage, natural selection kicked in over thousands of generations, and body hair gave way to bare skin populated by sweat glands. These became the body’s escape route for heat and created a further evolutionary advantage for these humans by making them more effective hunters and therefore, more attractive mates.

UV and vitamins

Moving to a sunnier environment meant greater exposure to ultraviolet light (UV) from the sun. UV breaks down folate, a vitamin that is vital for healthy pregnancies.

“When you don’t have hair, you have to figure out other ways to protect the skin,” explains Jablonski. This was especially important in the African tropics, where ultraviolet, carried in sunlight, hits the equator full-force.

Natural sunscreen

But just as some early humans got lucky by having less hair, some were also born with better protection from UV. Melanin is an ingredient in the skin that acts like a natural sunscreen, shielding folate from the harmful effects of UV light. The amount of melanin in skin determines its pigmentation: more of it makes darker brown skin, while less melanin makes paler skin. Those of our ancestors lucky enough to have more melanin were at a reproductive advantage, allowing them to spread the genes that encourage the production of darker skin.

But wait, there’s more

We know that our ancestors started moving out of Africa about 80 000 years ago. “They didn’t have a travel plan,” says Jablonski, “they were just going where the resources went.” They migrated north and south of the equator, where light hits the earth at increasingly slanted angles, resulting in weaker UV light. While this low angle made UV less damaging to folate, it also reduced bodily concentrations of Vitamin D, the “sunshine vitamin.”

Vitamin D is made naturally in the body when UV in sunlight hits the skin. Just like folate, it is vital for reproduction. But because humans had developed higher melanin levels to protect them from the tropical sun, they left Africa with a powerful melanin buffer that dangerously shut out the delivery of Vitamin D-producing UV.

The spread of color

However, those born with less melanin (and lighter skin) could still produce Vitamin D in environments with less sunlight. Having less melanin was also safe at higher latitudes, because UV there is not strong enough to damage folate. So, once again, natural selection took over: The genetically lucky grew stronger, spreading their light-skinned genes. Wherever direct sunlight was scarce, populations became paler — something Jablonski calls genetic “fine-tuning.” She explains: “We think that the transition was actually fairly short”, maybe 5,000 years — which is quick in evolutionary terms. The serious health impacts of having darker skin in high latitudes created a powerful evolutionary pressure that sped up the change.

But does it make sense?

Why then are there indigenous darker-skinned populations in less sunny parts of the world — for example, the Inuit in northern Canada? The answer appears to be that their diets are so loaded with Vitamin D-rich seafood that they get a surplus of the vitamin, making lighter skin unnecessary. This made adaptation equally unnecessary, and so in these populations, it stopped the evolution of skin color in its tracks.

What we have learned

The links between ultraviolet light and vitamins are an evolutionary balancing act, the consequences of which are so clear that there are maps showing how skin color varies with distance from the equator, creating a sepia rainbow.

Why should we care about skin color? For at least two reasons. The first is that the evolution of skin pigmentation shows the importance of vitamin health. More importantly, understanding the real causes of skin color variation is a powerful way to challenge some deeply entrenched — and false — ideas about race and the acceptability of racial discrimination.

Jablonski’s work shows that skin color, an attribute that has been at the center of so much conflict and suffering in human history, really is just skin deep. Our skin might make us look distinct on the outside, but it obscures a simple truth: Race is in fact nothing more than an environmental adaptation. It all boils down to sunlight and vitamins in the end.

Posted in: Life Science

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  1. “Race is nothing more than an environmental adaptation.”

    Well duh. Is there anyone who contends otherwise?

    In any event, I glad that we’ve at least moved beyond the ridiculous Politically Correct canard that “there’s no such thing” as race.

    Glenn Beaton, February 20, 2012 at 5:28 pm
  2. Possibly right on the evolution of skin color, but the assumption that race is only skin deep is nonsense. Different racial groups also have different skeletal structures, different risk factors for disease, different responses to alcohol consumption, different dentition, different hair, different responses to some foods, and on and on and on. There is presumably a greater genetic variation between human races than between varieties of dog. Draw your own conclusions from that.

    Rachelle, February 20, 2012 at 6:39 pm
  3. I understand that part of the process of losing our hair was during a period after coming down from the trees when we spent some time in the ocean surf, floating around up to our necks, and this helped us lose our hair and gain some fat. So we would soak in the surf, then hunt on the hot plains, then soak in the surf again.

    The lightest Caucasians perhaps developed as tribes of dark Assyrians moved into the Caucasus mountains, land of snow and ice, so the “white” people developed in those cold snowy lands. And the darkest Africans developed when tribes of Egyptians moved across the blistering deserts.

    So we are the children of the snow and the children of the sand.

    Surazeus Simon Seamount, February 20, 2012 at 9:45 pm
  4. Excellent explanation! Thanks!

    Viva, February 20, 2012 at 10:52 pm
  5. DUH. Most things about people in general that persist have a natural basis, be it dark skin for UV protection, pale skin for vitamin D with exceptions where diet is rich in vitamin D, or wariness toward those looking different (early one the closely related kin WERE the group and could be relied upon, others not).

    And in the last 5,000 years the human majority has lived in a cultural world, where culture evolves a lot more than the body does, so attitudes that may be based upon old patterns aren’t going to change due to physical evolution any more. Even if the effects of many of those attitudes have changed from probably positive to insane, as huge diverse and interconnected groups have become the norm over the last few centuries.

    john werneken, February 21, 2012 at 12:59 am
  6. Great article. I never knew uv breaks down folate. I will add this to my site.

    You mentioned folate is important for a healthy pregnancy. The Health Help section of LifeAmines.com proposes all the nutrients that are important in a healthy pregnancy. Check it out at http://www.lifeamines.com/health-help.html#pregnancy

    Ralph, February 21, 2012 at 2:11 am
  7. Glenn Beaton, “the ridiculous Politically Correct canard” about race you refer to is not so much that differences between groups of people do not exist, but that race as it is used by racist, that different groups of people are almost like different species does not exist. Some people have the need to use race as an weapon to harm others that they view to be inferior to themselves. I hope that you are not one of those people.

    Chris, February 21, 2012 at 2:13 am
  8. Science Line: The shortest distance between you and B.S.

    Rachelle, February 21, 2012 at 3:45 pm
  9. What explains the widely different facial features among people who evolved in different places around the world?

    Steve851, February 22, 2012 at 7:51 am
  10. Hey, do you have a source for that awesome pigment map? I’d like to take a closer look at that.

    Nick, July 24, 2012 at 3:45 pm
  11. MOST (99%) GENES ARE THE SAME IN ALL PEOPLE, BUT A SMALL NUMBER OF GENES (LESS THAN 1 PERCENT OF THE TOTAL) ARE SLIGHTLY DIFFERENT BETWEEN PEOPLE.

    Try to remember than when you think that there are any real differences between people. We have faces, a body, fingers, hands, feet, hair, teeth, you all look pretty similar from where I’m standing.

    And once more to drive you all mad:
    MOST (99%) GENES ARE THE SAME IN ALL PEOPLE, BUT A SMALL NUMBER OF GENES (LESS THAN 1 PERCENT OF THE TOTAL) ARE SLIGHTLY DIFFERENT BETWEEN PEOPLE.

    Just to make sure that’s good and drilled in there.

    Peace.

    Rob, November 1, 2012 at 1:44 am
  12. Also, I just saw this so i’m going to add it, and when I was saying a gene is turned on, I meant to say it’s expressed, so the right combo give you curly hair, and the right combo gives that person straight hair, don’t misunderstand though, same genes:

    Can genes be turned on and off in cells?

    Each cell expresses, or turns on, only a fraction of its genes. The rest of the genes are repressed, or turned off. The process of turning genes on and off is known as gene regulation. Gene regulation is an important part of normal development. Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell, for example. Gene regulation also allows cells to react quickly to changes in their environments. Although we know that the regulation of genes is critical for life, this complex process is not yet fully understood.

    Gene regulation can occur at any point during gene expression, but most commonly occurs at the level of transcription (when the information in a gene’s DNA is transferred to mRNA). Signals from the environment or from other cells activate proteins called transcription factors. These proteins bind to regulatory regions of a gene and increase or decrease the level of transcription. By controlling the level of transcription, this process can determine the amount of protein product that is made by a gene at any given time.

    Rob, November 1, 2012 at 1:48 am
  13. Thank you for this explanation

    Zizzi, January 6, 2013 at 4:16 pm
  14. To Rob,

    There is no denying that all humans share a staggerring majority of their genetic codes. Keep in mind however that, for instance, humans share approximately 90 % of their DNA with cats (domestic) and about 96% with chimapanzees. Yes, the one percent variation within homo sapiens is relatively small compared to variation between species, but in truth it is very signficant. Do not doubt the power of genetic variation. As said by Rachelle, earlier in the comments, “Different racial groups also have different skeletal structures, different risk factors for disease, different responses to alcohol consumption, different dentition, different hair, different responses to some foods, and on and on and on.” Anatomically, humans of different races are largely similar but disparities DO exist.

    Henry, April 18, 2013 at 12:16 pm
  15. Like, lol!

    Happy, May 7, 2013 at 10:30 am
  16. Forget that for skin ya’ll!

    Happy, May 7, 2013 at 10:31 am
  17. Great talk by Nina Jablonski on http://www.ted.com about how we came from Africa. Skin color has changed the further we have lived from the equator. Except that now we can jump on a plane and go anywhere in the world !

    Rufus Greenbaum, July 27, 2013 at 3:53 pm
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