A Vitamin D-lemma: The Formerly Racist Science of Skin Pigmentation

One of the most accessible bullets in the chamber of anyone who denies science is the fact that scientists don’t always (or even often) get things right on the first try. We all know that there were times in the past when people thought the sun revolved around the flat earth and that if a woman weighed as much as a duck she was probably a witch. In truth, science in vindicated by the fact that it is willing to change its collective mind in the face of new evidence. Occasionally though, there are topics where people should have known better a whole lot sooner than they did. Skin pigmentation is one of those topics.

Most famously in the blunders department, scientists (if it isn’t too much to call them that) used to use skin pigmentation to classify groups of people into “races.” Most of us are more than passingly familiar with the categories they came up with. Black, White, Asian, Latino, Brown, and Native American are the major denominations that tend to arise when we think about race. Historically, these divisions have been really bad news for most people. Actually, pretty much only white people made it through history free of persecution. 

For much longer than it made sense to believe so, people thought race was at the heart of who a person was. In fact we now know that race is entirely an artificial construct. As you move across the world and meet people from all its corners (spheres don’t have corners, it’s just an expression) you quickly realize that not only is there a complete continuum of people  between every stereotypical skin colour, there is also more variation within these so-called races than there is between them.

The reason that the illusion of races persisted for so long is because skin pigmentation is dictated by geographic location. Specifically (and very generally) groups of people with lighter skin have spent a lot of time living in areas far from the equator. As you move closer to this imaginary dotted line, you are likely to find groups of people with darker skin.

There are two-easy-to-understand reasons for this. Firstly, people get sunburns. As our ancestors moved out onto the hot African plains in search of food they needed to evolve a mechanism through which to expel excess heat. Over time, our ape-like ancestors lost most of their body hair and evolved the ability to sweat (as sweat evaporates it cools the skin). Unfortunately, as hair receded skin became more susceptible to UV radiation. As hilarious as it is to slap someone’s freshly reddened back when they are least expecting it, constant pain and the threat of skin cancer is no way to run a species. To cope with heightened exposure to the sun, human skin began to produce more melanin. 

Melanin is nature’s sun block. It protects the skin from burning and reduces the risk of cancer following exposure. It also darkens the colour of your skin. When normally pale people get a suntan, they are experiencing the same kind of transformation that all humans did in the distant past, it is just happening on a limited scale. No matter how long a white person stays in the sun, they will never look like Tyra Banks.

The problem with melanin is that occasionally it does too good of a job blocking the sun. As it turns out, exposure to UV light isn’t always a bad thing. In fact, it is one of the easiest and most reliable ways for a body to produce vitamin D. Vitamin D is essential to the normal growth of bones and the prevention of developmental problems like rickets (the softening of bones in young people). Since having softened bones is arguably worse than getting skin cancer (if you don’t have a strong skeleton, you aren’t likely to live long enough to get skin cancer), evolution needed to find a balance.

People who live far from the equator have to deal with seasons, and with seasons comes reduced daylight hours as we saw a few weeks ago. If your skin is full of melanin and you live at high-latitudes, you are likely to be vitamin D deficient and at high risk for rickets. To combat this, the bodies of people who live in such places have adapted and tend to produce less melanin, making them appear lighter in skin tone. This also explains the nice continuity in skin pigmentation we see between the equator and the poles.

So there it is. Skin colour, like every other characteristic we possess, is an adaptation; not a convenient indicator of personality traits. With the advent of sunscreen, vitamin supplements, and air travel it is also probably an adaptation with an expiry date. In another thousand years, we will probably all just be beige anyway.