The Evolution of Skin

It’s time for a mythconception and this week Eva Higginbotham has been picking apart the science of skin colour.

Eva -  From very pale to very dark, modern-day humans have a whole range of skin colours. And that’s just because having dark skin is better in hot countries to prevent skin cancer, and having light skin in cooler countries is better for making that essential vitamin D, right? Well, this is true, but it doesn’t actually explain how we evolved the variety of skin colours that we see today. Even with lots of time in the sun, you’re not too likely to get skin cancer until at least middle-age - and because evolution is all about who survives long enough to pass on their genes to the next generation, whether or not you got skin cancer by the time you had grandchildren shouldn’t really matter in an evolutionary sense. So, what’s the real story?

Before we were actually ‘humans’, we started off in Africa with pale pink skin covered by a generous serving of fur. And our expansive body hair did the hard work of protecting our skin from the sun’s strong UV rays. 

As we started losing our fur our skin gradually darkened, and this was to protect us from UV radiation. But, it wasn’t just to prevent skin cancer, the main reason we needed protection was to preserve our folate - a vitamin that is absolutely essential for a healthy life as a human, especially if you want to reproduce. For pregnant women is it exceptionally important, as a lack of folate during pregnancy can lead to serious spinal defects.

And importantly, UV radiation is very good at breaking down folate. So if you were an early human living in Africa and you had pale skin, you weren’t going to be making too many babies because your folate would be constantly depleted by the hot sun. But, if you had darker skin, you were more protected from the sun’s UV rays and so able to hold onto your folate better, increasing your fertility and making it more likely that you’d have a healthy baby. Our darker skinned forebears had the evolutionary edge over the lighter skinned as a result, and so by the time our ancestors had evolved to be homo sapiens, the species we are today, everyone had dark skin.

So, the reason we evolved dark skin in the first place wasn’t really to do with preventing skin cancer, the much more important factor was that having darker skin protected people from depleting their folate. Now, once humans started dispersing around the globe to countries with weaker sunlight, they had to balance the need to protect their folate with their need for vitamin D - another essential vitamin for humans which needs the opposite of folate, lots of sunlight! And ultimately, the range of skin colours we see today all come from the competing needs to protect our folate and make our vitamin D, not to stop us getting skin cancer. Still, since we are living much longer nowadays, it’s best to not skimp on the suncream when getting out and about in summer sun.