The science behind skin color, Part One
Every person in the human race is from the same species, no matter what features they show on the outside (or inside).
To science, there really is no such thing as Native Americans, Eskimos, African Americans or Caucasians. All of these terms are made up by humans and have no scientific basis.
However, it is obvious that not all humans look exactly alike. And it certainly appears that humans have evolved unique physical characteristics based on where their ancestors lived.
While humans are humans no matter where their ancestors lived, science can now explain why humans in certain parts of the world look differently on the outside than other humans from different parts of the world. It turns out that our human race has experienced a wild and fascinating ride when it comes to skin color.
Geography
Every bit of the human skin color story is connected to geography, as it depends on where the humans were on Earth. Also important to remember, we are talking about a period of time where any human traveling was done by foot and typically in large groups. So people did not randomly relocate to new places on Earth as often as they do now.
All pale skinned — and hairy
At the beginning of the human race, we all had pale skin. However, on top of that pale skin was a thick layer of hair. Humans did not wear clothing, so the hair protected them from the weather and kept them a little warmer. This phenomenon is pretty much exactly how most animals exist today — a body covered in hair on top of pale skin.
All dark skinned — less hair
Over time, humans started to either prefer or not need all the hair covering their body, and humans started becoming less hairy. This was likely due to the warm climate they lived in. This exposed more and more of their pale skin. It is believed that our very first human ancestors lived near the Earth’s equator. This part of the Earth experiences a lot of solar radiation because the sun’s rays hit the surface of the equator straight on. Ultraviolet light can penetrate our skin and damage our DNA.
Damaged DNA can cause mutations, which can cause cancer. The pigment in your skin is determined by the type of melanin in your cells. Melanin is a molecule that gives your skin its color. This molecule can also block out the harmful UV radiation from damaging your cell’s DNA by lining up around the nucleus and acting as a shield.
Originally, humans all had phail melanin, which is characterized by only having a little pigment. Phail melanin is not very dense, and therefore allows quite a bit of UV light to penetrate all the way into the cell’s genetic material. As we know, this can cause cancer.
However, this does not explain why humans started to develop darker skin, because skin cancer usually occurs after a person has had babies and passed their genetic material onto their offspring. A person who dies from skin cancer after they have had children does nothing to shift the genetics or traits of future offspring.
Folate is the secret
It turns out that a seemingly boring chemical called folate held the secret to skin color evolution in humans. Folate was found to be essential to developing babies. It was also found that ultraviolet light broke down folate. The mystery was solved when scientists realized that the UV light in light-skinned humans was destroying folate and developing babies were not surviving or were experiencing severe birth defects. In these cases, the DNA was not being passed down.
At some point, a new type of melanin evolved and it was called umelanin. This new melanin was far darker and denser and blocked out far more UV light from the nucleus of the cells. Humans with umelanin had darker skin and their babies were developing better than those parents with light skin. Natural selection favored the darker skin and, over time, the human population all had dark skin.
So, at this point in history, we have a population of humans all with dark skin living near the Earth’s equator. There are no human populations with light skin and some with dark skin. It's just that humans simply have dark skin.
The story obviously does not end there. Come back next week for the conclusion of the fascinating science behind human skin color.
Mike Szydlowski is science coordinator for Columbia Public Schools.
TIME FOR A POP QUIZ
1. Why is it unlikely that skin cancer played a part in shifting skin colors over time?
2. Did the early humans decide that the changes in hair and skin color needed to change?
3. What was the consequence of humans losing body hair?
4. What are the names and differences between the two types of melanin in cells?
5. What advantage did darker skin give humans?
LAST WEEK’S POP QUIZ ANSWERS
1. What is the most important task in the animal world?
Reproducing is the number one task in the animal world.
2. If 1,000 octopi (half male, half female) mate, approximately how many new adult octopi would develop? What does this mean for the overall octopi population?
On average, only two baby octopi survive into adulthood so 1,000 adult octopi would produce about 1,000 new adults. For this reason, the octopi population does not typically increase.
3. Why do you think octopi lay and care for so many eggs if only a couple survive?
Because it is so difficult for baby octopi to survive, the adults have to produce many babies in hopes that at least a few survive.
4. How are koala bears able to eat leaves that are not edible to almost everything else?
Koala bears have special microbes in their gut that help them digest this very tough leaf.
5. What do human moms do to help human babies survive into adulthood?
What don’t they do? Human moms provide food and shelter for several years while also educating the baby on how to speak and do many other things needed for life.